### Third-level heading
#### Fourth-level heading
Paragraphs
Example
This is a paragraph. There are no spaces before the word 'This'.
This is another paragraph. The first line has two sentences.
The entire paragraph has two lines and three sentences.
Line breaks in the input,
Make line breaks in the output,
Like this.
Formatted
This is a paragraph. There are no spaces before the word 'This'.
This is another paragraph. The first line has two sentences. The entire paragraph has two lines and
three sentences.
Line breaks in the input,
Make line breaks in the output,
Like this.
Italicized and bold text
Example
For italics, surround text with underscores:
_hello, world_.
For bold, surround text with two asterisks:
**hello, world**.
You can also combine them:
_**hello**_ and **_goodbye_**
Formatted
For italics, surround text with underscores:
hello, world.
For bold, surround text with two asterisks:
hello, world.
You can also combine them:
hello and goodbye
Ordered lists
Example
We are about to start an ordered list.
1. Ordered lists are indented 2 spaces.
1. Subitems are indented 2 more spaces (4 in all).
2. The next item in the list starts with the next number.
3. And so on...
#### Formatted
We are about to start an ordered list.
1. Ordered lists are indented 2 spaces.
1. Subitems are indented 2 more spaces (4 in all for a second level item).
2. The next item in the list starts with the next number.
3. And so on...
#### Example
We are about to start an unordered list.
Like ordered lists, unordered lists are also indented 2 spaces.
Unlike ordered lists, unordered lists use stars instead of numbers.
Sub items are indented 2 more spaces.
Here's another sub item.
Formatted
We are about to start an unordered list.
Like ordered lists, unordered lists are also indented 2 spaces.
Unlike ordered lists, unordered lists use stars instead of numbers.
Sub items are indented 2 more spaces.
Here's another sub item.
Links
Automatic links
The simplest way to create a link is to just type it in:
Example
http://ccl.northwestern.edu/netlogo/
Formatted
http://ccl.northwestern.edu/netlogo/
Links with text
If you want to use your own text for the link, here's how:
[link text here](link.address.here)
Example
[NetLogo](http://ccl.northwestern.edu/netlogo/)
Formatted
NetLogo
Local links
It is also possible to link to a page on your computer, instead of a page somewhere on the Internet.
Local links have this form:
[alt text](file:path)
Any spaces in the path must be converted to %20. For example, this:
file:my page.html
must be written as:
file:my%20page.html
The path is relative to the directory that the model file is in.
Example
The easiest way to link to files on your computer is to put them into the same directory as your model.
Assuming you have a file named index.html in the same directory as your model, the link would look
like this:
[Home](file:index.html)
Example
Here is another example where the file lives in a directory called docs, and docs is in the same
directory as your model:
[Home](file:docs/index.html)
Images
Images are very similar to links, but have an exclamation point in front:
(The alternate text is the text that gets displayed if the image is not found.)
Example
Formatted
Local images
Also very similar to links, it is possible to display an image on your computer instead of an image
somewhere on the Internet. Assuming you have an image named image.jpg, local images look like this:
The path is relative to the directory that the model file is in.
As with local links, any spaces in the name of the file or the path must be converted to %20.
Example
Like local links, the easiest way to display images on your computer is to put them into the same
directory as your model. This example displays the image "Perspective Example.png", which resides in
the same directory as this model (Info Tab Example).
Formatted
Block quotations
Consecutive lines starting with > will become block quotations.
You can put whatever text you like inside of it and you can also style it.
Example
> Let me see: four times five is twelve, and four times six is thirteen,
> and four times seven is --- _oh dear!_
> I shall never get to twenty at that rate!
Formatted
Let me see: four times five is twelve, and four times six is thirteen,
and four times seven is -- oh dear!
I shall never get to twenty at that rate!
Code
To include a short piece of code in a sentence, surround it with backticks (`).
Example
You can create a single turtle with the `crt 1` command.
Formatted
You can create a single turtle with the crt 1 command.
Code blocks
It is also possible to have blocks of code. To create a code block, indent every line of the block by 4
spaces. Another way is to surround it with a three backticks line before and after the block. (If you don't
want your code to be colored as NetLogo code, add text after the first three backticks.)
Example
About to start the code block.
Leave a blank line after this one, and then put the code block:
; a typical go procedure
to go
ask turtles
[ fd 1 ]
tick
end
or:
About to start the code block.
Leave a blank line after this one, and then put the code block:
```
; a typical go procedure
to go
ask turtles
[ fd 1 ]
tick
end
```
Formatted
About to start the code block.
Leave a blank line after this one, and then put the code block:
; a typical go procedure
to go
ask turtles
[ fd 1 ]
tick
end
Superscripts and subscripts
Superscripts and subscripts are useful for writing formulas, equations, footnotes and more. Subscripts
appear half a character below the baseline, and are written using the HTML tag . Superscripts
appear half a character above the baseline, and are written using the HTML tag .
Example
H2O
2x4 + x2
WWW[1]
Formatted
H 2O
2x4 + x2 + 42
WWW[1]
Notes on usage
Paragraphs, lists, code blocks and other features should be separated from each other with a
blank line. If you find that something isn't formatted the way you expected, it might be because
you need to add a blank line before it.
To prevent a special character from being treated as markup, put a backslash (\) before it.
We use GitHub flavored newlines (https://github.github.com/github-flavored-markdown/) instead
of traditional Markdown handling of newlines. This means that newlines are treated as real line
breaks, instead of being combined with the previous line into a single paragraph.
Other features
Markdown has additional features that we have not shown here.
We have tested the features shown above on a variety of systems. If you use other Markdown features,
you may find that they work on your computer, or not. Even a feature that works on your computer
might work differently, or not work at all, for someone with a different operating system or Java virtual
machine.
If you want all NetLogo users to be able to read your Info tab, use only the features shown above.
More information about Markdown is at http://daringfireball.net/projects/markdown/. For rendering
Markdown, NetLogo uses the Pegdown library.
Code Tab Guide
The Code tab is where the code for the model is stored. Commands you only want to use
immediately go in the Command Center; commands you want to save and use later, over and
over again, are found in the Code tab.
To determine if the code has any errors, you may press the "Check" button. If there are any
syntax errors, the Code tab will turn red, the code that contains the error will be highlighted,
and an error message will appear.
Switching tabs also causes the code to be checked, so if you just switch tabs, pressing the
Check button first isn't necessary.
To find a fragment of code in the procedures, click on the "Find" button in the Code toolbar
and the Find dialog will appear.
You may enter a word or phrase to find, and optionally also a new word or phrase to replace it
with. The "Ignore case" checkbox controls whether the capitalization must be the same to
indicate a match.
If the "Wrap around" checkbox is checked, the entire Code tab will be checked for the phrase,
starting at the cursor position. When it reaches the end it will return to the top, otherwise only
the area from the cursor position to the end of the Code tab will be searched. The "Next" and
"Previous" buttons will move down and up to find another occurrence of the search phrase.
"Replace" changes the currently selected phrase with the replace phrase and "Replace &
Find" changes the selected phrase and moves to the next occurrence. "Replace All" will
change all instances of the find phrase in the search area with the replace phrase.
To find a particular procedure definition in your code, use the "Procedures" popup menu in the
Code tab. The menu lists all procedures in alphabetical order.
The "Shift Left", "Shift Right", "Comment", and "Uncomment" items on the Edit menu are used
in the Code tab to change the indentation level of your code or add and remove semicolons,
which mark comments, from sections of code.
For more information about writing procedures, read Tutorial #3: Procedures and the
Programming Guide.
Included Files Menu
Caution: The includes facility is new and experimental.
When you add the __includes keyword to a model a menu to the right of the procedures menu
appears. This is the "Included Files" menu which lists all the NetLogo source files (.nls)
included in this file. You can make this menu always visible using the Preferences dialog.
You can choose a file name from the menu to open a tab for that file, or you can open a new
or existing file using New Source File and Open Source File, respectively.
Once you've opened new tabs they become accessible from the Tabs menu, and you can use
the keyboard to move from tab to tab (Command + number on Mac, Control + number on
other operating systems).
Automatic indentation
When the Indent Automatically checkbox is selected, NetLogo will automatically attempt to
align your code in a logically structured format. For example, when you open a set of square
brackets "[" (perhaps after an if statement), NetLogo will automatically add spaces so that the
following lines of code are two spaces further indented than the bracket. When you close the
square brackets the closing bracket will be lined up with the matching open bracket.
NetLogo will try to indent the code as you type, but you can also press the tab key anywhere
on any line to ask NetLogo to indent the line immediately. Or, you can select a whole region of
code and press the tab key to re-indent all of it.
Programming Guide
This section describes the NetLogo programming language in detail.
The Code Example models mentioned throughout can be found in the Code Examples section of the
Models Library.
Agents
Procedures
Variables
Tick counter
Colors
Ask
Agentsets
Breeds
Buttons
Lists
Math
Random numbers
Turtle shapes
Link shapes
View updates
Plotting
Strings
Output
File I/O
Movies
Perspective
Drawing
Topology
Links
Anonymous procedures
Ask-Concurrent
User Interaction Primitives
Tie
Multiple source files
Syntax
Agents
The NetLogo world is made up of agents. Agents are beings that can follow instructions.
In NetLogo, there are four types of agents: turtles, patches, links, and the observer.
Turtles are agents that move around in the world. The world is two dimensional and is divided up into a
grid of patches. Each patch is a square piece of "ground" over which turtles can move. Links are agents
that connect two turtles. The observer doesn't have a location -- you can imagine it as looking out over
the world of turtles and patches.
The observer doesn't observe passively -- it gives instructions to the other agents.
When NetLogo starts up, there are no turtles. The observer can make new turtles. Patches can make
new turtles too. (Patches can't move, but otherwise they're just as "alive" as turtles.)
Patches have coordinates. The patch at coordinates (0, 0) is called the origin and the coordinates of the
other patches are the horizontal and vertical distances from this one. We call the patch's coordinates
pxcor and pycor. Just like in the standard mathematical coordinate plane, pxcor increases as you move
to the right and pycor increases as you move up.
The total number of patches is determined by the settings min-pxcor, max-pxcor, min-pycor, and maxpycor When NetLogo starts up, min-pxcor, max-pxcor, min-pycor, and max-pycor are -16, 16, -16, and 16
respectively. This means that pxcor and pycor both range from -16 to 16, so there are 33 times 33, or
1089 patches total. (You can change the number of patches with the Settings button.)
Turtles have coordinates too: xcor and ycor. A patch's coordinates are always integers, but a turtle's
coordinates can have decimals. This means that a turtle can be positioned at any point within its patch; it
doesn't have to be in the center of the patch.
Links do not have coordinates. Every link has two ends, and each end is a turtle. If either turtle dies, the
link dies too. A link is represented visually as a line connecting the two turtles.
Procedures
In NetLogo, commands and reporters tell agents what to do. A command is an action for an agent to
carry out, resulting in some effect. A reporter is instructions for computing a value, which the agent then
"reports" to whoever asked it.
Typically, a command name begins with a verb, such as "create", "die", "jump", "inspect", or "clear".
Most reporter names are nouns or noun phrases.
Commands and reporters built into NetLogo are called primitives. The NetLogo Dictionary has a
complete list of built-in commands and reporters.
Commands and reporters you define yourself are called procedures. Each procedure has a name,
preceded by the keyword to or to-report, depending on whether it is a command procedure or a
reporter procedure. The keyword end marks the end of the commands in the procedure. Once you
define a procedure, you can use it elsewhere in your program.
Many commands and reporters take inputs -- values that the command or reporter uses in carrying out
its actions or computing its result.
Here are two command procedures:
to setup
clear-all
create-turtles 10
reset-ticks
end
to go
ask turtles [
fd 1
rt random 10
lt random 10
]
tick
end
;; forward 1 step
;; turn right
;; turn left
Note the use of semicolons to add "comments" to the program. Comments can make your code easier
to read and understand, but they don't affect its behavior.
In this program,
setup and go are user-defined commands.
clear-all, create-turtles , reset-ticks, ask, lt
("left turn"), rt ("right turn") and tick, are all
primitive commands.
random and turtles are primitive reporters. random takes a single number as an input and reports a
random integer that is less than the input (in this case, between 0 and 9). turtles reports the
agentset consisting of all the turtles. (We'll explain about agentsets later.)
setup
and go can be called by other procedures, or by buttons, or from the Command Center.
Many NetLogo models have a once button that calls a procedure called setup and a forever button that
calls a procedure called go.
In NetLogo, you may specify which agents -- turtles, patches, or links -- are to run each command. If you
don't specify, the code is run by the observer. In the code above, the observer uses ask to make the set
of all turtles run the commands between the square brackets.
and create-turtles can only be run by the observer. fd, on the other hand, can only be run
by turtles. Some other commands and reporters, such as set and ticks, can be run by different agent
types.
clear-all
Here are some more advanced features you can take advantage of when defining your own procedures.
Procedures with inputs
Procedures can take inputs, just like many primitives do. To create a procedure that accepts inputs, put
their names in square brackets after the procedure name. For example:
to draw-polygon [num-sides len]
pen-down
repeat num-sides [
fd len
rt 360 / num-sides
]
end
;; turtle procedure
Elsewhere in the program, you might use the procedure by asking the turtles to each draw an octagon
with a side length equal to its who number:
ask turtles [ draw-polygon 8 who ]
Reporter procedures
Just like you can define your own commands, you can define your own reporters. You must do two
special things. First, use to-report instead of to to begin your procedure. Then, in the body of the
procedure, use report to report the value you want to report.
to-report absolute-value [number]
ifelse number >= 0
[ report number ]
[ report (- number) ]
end
Variables
Agent variables
Agent variables are places to store values (such as numbers) in an agent. An agent variable can be a
global variable, a turtle variable, a patch variable, or a link variable.
If a variable is a global variable, there is only one value for the variable, and every agent can access it.
You can think of global variables as belonging to the observer.
Turtle, patch, and link variables are different. Each turtle has its own value for every turtle variable. The
same goes for patches and links.
Some variables are built into NetLogo. For example, all turtles and links have a color variable, and all
patches have a pcolor variable. (The patch variable begins with "p" so it doesn't get confused with the
turtle variable, since turtles have direct access to patch variables.) If you set the variable, the turtle or
patch changes color. (See next section for details.)
Other built-in turtle variables including xcor, ycor, and heading . Other built-in patch variables include
pxcor and pycor. (There is a complete list here.)
You can also define your own variables. You can make a global variable by adding a switch, slider,
chooser, or input box to your model, or by using the globals keyword at the beginning of your code, like
this:
globals [score]
You can also define new turtle, patch and link variables using the turtles-own , patches-own and linksown keywords, like this:
turtles-own [energy speed]
patches-own [friction]
links-own [strength]
These variables can then be used freely in your model. Use the set command to set them. (Any variable
you don't set has a starting value of zero.)
Global variables can be read and set at any time by any agent. As well, a turtle can read and set patch
variables of the patch it is standing on. For example, this code:
ask turtles [ set pcolor red ]
causes every turtle to make the patch it is standing on red. (Because patch variables are shared by
turtles in this way, you can't have a turtle variable and a patch variable with the same name.)
In other situations where you want an agent to read a different agent's variable, you can use of.
Example:
show [color] of turtle 5
;; prints current color of turtle with who number 5
You can also use of with a more complicated expression than just a variable name, for example:
show [xcor + ycor] of turtle 5
;; prints the sum of the x and y coordinates of
;; turtle with who number 5
Local variables
A local variable is defined and used only in the context of a particular procedure or part of a procedure.
To create a local variable, use the let command. If you use let at the top of a procedure, the variable
will exist throughout the procedure. If you use it inside a set of square brackets, for example inside an
"ask", then it will exist only inside those brackets.
to swap-colors [turtle1 turtle2]
let temp [color] of turtle1
ask turtle1 [ set color [color] of turtle2 ]
ask turtle2 [ set color temp ]
end
Tick counter
In many NetLogo models, time passes in discrete steps, called "ticks". NetLogo includes a built-in tick
counter so you can keep track of how many ticks have passed.
The current value of the tick counter is shown above the view. (You can use the Settings button to hide
the tick counter, or change the word "ticks" to something else.)
In code, to retrieve the current value of the tick counter, use the ticks reporter. The tick command
advances the tick counter by 1. The clear-all command clears the tick counter along with everything
else.
When the tick counter is clear, it's an error to try to read or modify it. Use the reset-ticks command
when your model is done setting up, to start the tick counter.
If your model is set to use tick-based updates, then the tick command will usually also update the view.
See the later section, View Updates.
When to tick
Use reset-ticks at the end of your setup procedure.
Use tick at the end of your go procedure.
to setup
clear-all
create-turtles 10
reset-ticks
end
to go
ask turtles [ fd 1 ]
tick
end
Fractional ticks
In most models, the tick counter starts at 0 and goes up 1 at a time, from integer to integer. But it's also
possible for the tick counter to take on in-between floating point values.
To advance the tick counter by a fractional amount, use the tick-advance command. This command
takes a numeric input specifying how far to advance the tick counter.
A typical use of fractional ticks is to approximate continuous or curved motion. See, for example, the
GasLab models in the Models Library (under Chemistry & Physics). These models calculate the exact
time at which a future event is to occur, then advance the tick counter to exactly that time.
Colors
NetLogo represents colors in different ways. A color can be number in the range 0 to 140, with the
exception of 140 itself. Below is a chart showing the range of such colors you can use in NetLogo.
The chart shows that:
Some of the colors have names. (You can use these names in your code.)
Every named color except black and white has a number ending in 5.
On either side of each named color are darker and lighter shades of the color.
0 is pure black. 9.9 is pure white.
10, 20, and so on are all so dark they are very nearly black.
19.9, 29.9 and so on are all so light they are very nearly white.
Code Example: The color chart was made in NetLogo with the Color Chart Example model.
If you use a number outside the 0 to 140 range, NetLogo will repeatedly add or subtract 140 from the
number until it is in the 0 to 140 range. For example, 25 is orange, so 165, 305, 445, and so on are
orange too, and so are -115, -255, -395, etc. This calculation is done automatically whenever you set
the turtle variable color or the patch variable pcolor. Should you need to perform this calculation in
some other context, use the wrap-color primitive.
If you want a color that's not on the chart, more exist between the integers. For example, 26.5 is a shade
of orange halfway between 26 and 27. This doesn't mean you can make any color in NetLogo; the
NetLogo color space is only a subset of all possible colors. It contains only a fixed set of discrete hues
(one hue per row of the chart). Starting from one of those hues, you can either decrease its brightness
(darken it) or decrease its saturation (lighten it), but you cannot decrease both brightness and saturation.
Also, only the first digit after the decimal point is significant. Thus, color values are rounded down to the
next 0.1, so for example, there's no visible difference between 26.5 and 26.52 or 26.58.
Color primitives
There are a few primitives that are helpful for working with colors.
We have already mentioned the wrap-color primitive.
The scale-color primitive is useful for converting numeric data into colors.
shade-of?
orange 27
will tell you if two colors are both "shades" of the same basic hue. For example, shade-of?
is true, because 27 is a lighter shade of orange.
Code Example: Scale-color Example demonstrates the scale-color reporter.
RGB and RGBA Colors
NetLogo also represents colors as RGB (red/green/blue) lists and RGBA (red/green/blue/alpha) lists.
When using RGB colors the full range of colors is available to you. RGBA colors allow all the colors that
RGB allows and you can also vary the transparency of a color. RGB and RGBA lists are made up of
three or four integers, respectively, between 0 and 255 if a number is outside that range 255 is
repeatedly subtracted until it is in the range. You can set any color variables in NetLogo (color for turtles
and links and pcolor for patches) to an RGB list and that agent will be rendered appropriately. So you
can set the color of patch 0 0 to pure red using the following code:
set pcolor [255 0 0]
Turtles, links, and labels can all contain RGBA lists as their color variables, however, patches cannot
have RGBA pcolors You can set the color of a turtle to be approximately half transparent pure red with
the following code:
set color [255 0 0 125]
You can convert from a NetLogo color to RGB or HSB (hue/saturation/brightness) using extract-hsb and
extract-rgb. You can use rgb to generate rgb lists and hsb to convert from an HSB color to RGB.
Since many colors are missing from the NetLogo color space, approximate-hsb and approximate-rgb
often can't give you the exact color you ask for, but they try to come as close as possible.
Example: you can change any turtle from it's existing NetLogo color to a half transparent version of that
color using:
set color lput 125 extract-rgb color
Code Examples: HSB and RGB Example (lets you experiment with the HSB and RGB color
systems), Transparency Example
Color Swatches dialog
The Color Swatches dialog helps you experiment with and choose colors. Open it by choosing Color
Swatches on the Tools Menu.
When you click on a color swatch (or a color button), that color will be shown against other colors. In the
bottom left, the code for the currently selected color is displayed (for example, red + 2 ) so you can copy
and paste it into your code. On the bottom right there are three increment options, 1, 0.5, and 0.1.
These numbers indicate the difference between two adjacent swatches. When the increment is 1 there
are 10 different shades in each row; when the increment is 0.1 there are 100 different shades in each
row. 0.5 is an intermediate setting.
Ask
NetLogo uses the ask command to give commands to turtles, patches, and links. All code to be run by
turtles must be located in a turtle "context". You can establish a turtle context in any of three ways:
In a button, by choosing "Turtles" from the popup menu. Any code you put in the button will be run
by all turtles.
In the Command Center, by choosing "Turtles" from the popup menu. Any commands you enter
will be run by all the turtles.
By using ask turtles, hatch, or other commands which establish a turtle context.
The same goes for patches, links, and the observer, except that you cannot ask the observer. Any code
that is not inside any ask is by default observer code.
Here's an example of the use of ask in a NetLogo procedure:
to setup
clear-all
create-turtles 100
;; create 100 turtles with random headings
ask turtles
[ set color red
;; turn them red
fd 50 ]
;; spread them around
ask patches
[ if pxcor > 0
;; patches on the right side
[ set pcolor green ] ] ;; of the view turn green
reset-ticks
end
The models in the Models Library are full of other examples. A good place to start looking is in the Code
Examples section.
Usually, the observer uses ask to ask all turtles, all patches or all links to run commands. You can also
use ask to have an individual turtle, patch or link run commands. The reporters turtle, patch, link and
patch-at are useful for this technique. For example:
to setup
clear-all
crt 3
;; make 3 turtles
ask turtle 0
;; tell the first one...
[ fd 1 ]
;; ...to go forward
ask turtle 1
;; tell the second one...
[ set color green ]
;; ...to become green
ask turtle 2
;; tell the third one...
[ rt 90 ]
;; ...to turn right
ask patch 2 -2
;; ask the patch at (2,-2)
[ set pcolor blue ]
;; ...to become blue
ask turtle 0
;; ask the first turtle
[ ask patch-at 1 0
;; ...to ask patch to the east
[ set pcolor red ] ]
;; ...to become red
ask turtle 0
;; tell the first turtle...
[ create-link-with turtle 1 ] ;; ...make a link with the second
ask link 0 1
;; tell the link between turtle 0 and 1
[ set color blue ]
;; ...to become blue
reset-ticks
end
Every turtle created has a who number. The first turtle created is number 0, the second turtle number 1,
and so forth.
The turtle primitive reporter takes a who number as an input, and reports the turtle with that who
number. The patch primitive reporter takes values for pxcor and pycor and reports the patch with those
coordinates. The link primitive takes two inputs, the who numbers of the two turtles it connects. And the
patch-at primitive reporter takes offsets: distances, in the x and y directions, from the first agent. In the
example above, the turtle with who number 0 is asked to get the patch east (and no patches north) of
itself.
You can also select a subset of turtles, or a subset of patches, or a subset of links and ask them to do
something. This involves using agentsets. The next section explains them in detail.
When you ask a set of agents to run more than one command, each agent must finish before the next
agent starts. One agent runs all of the commands, then the next agent runs all of them, and so on. For
example, if you write:
ask turtles
[ fd 1
set color red ]
first one turtle moves and turns red, then another turtle moves and turns red, and so on.
But if you write it this way:
ask turtles [ fd 1 ]
ask turtles [ set color red ]
first all the turtles move, then they all turn red.
Agentsets
An agentset is exactly what its name implies, a set of agents. An agentset can contain either turtles,
patches or links, but not more than one type at once.
An agentset is not in any particular order. In fact, it's always in a random order. And every time you use
it, the agentset is in a different random order. This helps you keep your model from treating any
particular turtles, patches or links differently from any others (unless you want them to be). Since the
order is random every time, no one agent always gets to go first.
You've seen the turtles primitive, which reports the agentset of all turtles, the patches primitive, which
reports the agentset of all patches and the links primitive which reports the agentset of all links.
But what's powerful about the agentset concept is that you can construct agentsets that contain only
some turtles, some patches or some links. For example, all the red turtles, or the patches with pxcor
evenly divisible by five, or the turtles in the first quadrant that are on a green patch or the links
connected to turtle 0. These agentsets can then be used by ask or by various reporters that take
agentsets as inputs.
One way is to use turtles-here or turtles-at, to make an agentset containing only the turtles on my
patch, or only the turtles on some other patch at some x and y offsets. There's also turtles-on so you
can get the set of turtles standing on a given patch or set of patches, or the set of turtles standing on the
same patch as a given turtle or set of turtles.
Here are some more examples of how to make agentsets:
;; all other turtles:
other turtles
;; all other turtles on this patch:
other turtles-here
;; all red turtles:
turtles with [color = red]
;; all red turtles on my patch
turtles-here with [color = red]
;; patches on right side of view
patches with [pxcor > 0]
;; all turtles less than 3 patches away
turtles in-radius 3
;; the four patches to the east, north, west, and south
patches at-points [[1 0] [0 1] [-1 0] [0 -1]]
;; shorthand for those four patches
neighbors4
;; turtles in the first quadrant that are on a green patch
turtles with [(xcor > 0) and (ycor > 0)
and (pcolor = green)]
;; turtles standing on my neighboring four patches
turtles-on neighbors4
;; all the links connected to turtle 0
[my-links] of turtle 0
Note the use of other to exclude this agent. This is common.
Once you have created an agentset, here are some simple things you can do:
Use ask to make the agents in the agentset do something
Use any? to see if the agentset is empty
Use all? to see if every agent in an agentset satisfies a condition.
Use count to find out exactly how many agents are in the set
And here are some more complex things you can do:
Pick a random agent from the set usingone-of. For example, we can make a randomly chosen
turtle turn green:
ask one-of turtles [ set color green ]
Or tell a randomly chosen patch to sprout a new turtle:
ask one-of patches [ sprout 1 ]
Use the max-one-of or min-one-of reporters to find out which agent is the most or least along some
scale. For example, to remove the richest turtle, you could say
ask max-one-of turtles [sum assets] [ die ]
Make a histogram of the agentset using thehistogram command (in combination with of).
Use of to make a list of values, one for each agent in the agentset. Then use one of NetLogo's list
primitives to do something with the list. (See the "Lists" section below.) For example, to find out
how rich turtles are on the average, you could say
show mean [sum assets] of turtles
Use turtle-set, patch-set and link-set reporters to make new agentsets by gathering together
agents from a variety of possible sources.
Use no-turtles, no-patches and no-links reporters to make empty agentsets.
Check whether two agentsets are equal using = or !=.
Use member? to see whether a particular agent is a member of an agentset.
This only scratches the surface. See the Models Library for many more examples, and consult the
NetLogo Dictionary for more information about all of the agentset primitives.
More examples of using agentsets are provided in the individual entries for these primitives in the
NetLogo Dictionary.
Special agentsets
The agentsets turtles and links have special behavior because they always hold the sets of all turtles
and all links. Therefore, these agentsets can grow.
The following interaction shows the special behavior. Assume the Code tab has globals [g]. Then:
observer>
observer>
observer>
observer>
5
observer>
observer>
10
observer>
observer>
10
observer>
observer>
10
observer>
15
clear-all
create-turtles 5
set g turtles
print count g
create-turtles 5
print count g
set g turtle-set turtles
print count g
create-turtles 5
print count g
print count turtles
The turtles agentset grows when new turtles are born, but other agentsets don't grow. If I write turtleset turtles , I get a new, normal agentset containing just the turtles that currently exist. New turtles don't
join when they're born.
Breed agentsets are special in the same way as turtles and links. Breeds are introduced and
explained below.
Agentsets and lists
Earlier, we said that agentsets are always in random order, a different random order every time. If you
need your agents to do something in a fixed order, you need to make a list of the agents instead. See
the Lists section below.
Code Example: Ask Ordering Example
Breeds
NetLogo allows you to define different "breeds" of turtles and breeds of links. Once you have defined
breeds, you can go on and make the different breeds behave differently. For example, you could have
breeds called sheep and wolves, and have the wolves try to eat the sheep or you could have link breeds
called streets and sidewalks where foot traffic is routed on sidewalks and car traffic is routed on streets.
You define turtle breeds using the breed keyword, at the top of the Code tab, before any procedures:
breed [wolves wolf]
breed [sheep a-sheep]
You can refer to a member of the breed using the singular form, just like the turtle reporter. When
printed, members of the breed will be labeled with the singular name.
Some commands and reporters have the plural name of the breed in them, such as create-.
Others have the singular name of the breed in them, such as
The order in which breeds are declared is also the order in which they are layered in the view. So
breeds defined later will appear on top of breeds defined earlier; in this example, sheep will be drawn
over wolves.
When you define a breed such as sheep, an agentset for that breed is automatically created, so that all of
the agentset capabilities described above are immediately available with the sheep agentset.
The following new primitives are also automatically available once you define a breed: create-sheep ,
hatch-sheep, sprout-sheep , sheep-here, sheep-at , sheep-on , and is-a-sheep?.
Also, you can use sheep-own to define new turtle variables that only turtles of the given breed have. (It's
allowed for more than one breed to own the same variable.)
A turtle's breed agentset is stored in the breed turtle variable. So you can test a turtle's breed, like this:
if breed = wolves [ ... ]
Note also that turtles can change breeds. A wolf doesn't have to remain a wolf its whole life. Let's
change a random wolf into a sheep:
ask one-of wolves [ set breed sheep ]
The set-default-shape primitive is useful for associating certain turtle shapes with certain breeds. See
the section on shapes below.
Who numbers are assigned irrespective of breeds. If you already have a frog 0, then the first mouse will
be mouse 1 , not mouse 0 , since the who number 0 is already taken.
Here is a quick example of using breeds:
breed [mice mouse]
breed [frogs frog]
mice-own [cheese]
to setup
clear-all
create-mice 50
[ set color white
set cheese random 10 ]
create-frogs 50
[ set color green ]
reset-ticks
end
Code Example: Breeds and Shapes Example
Link breeds
Link breeds are very similar to turtle breeds, however, there are a few differences.
When you declare a link breed you must declare whether it is a breed of directed or undirected links by
using the directed-link-breed and undirected-link-breed keywords.
directed-link-breed [streets street]
undirected-link-breed [friendships friendship]
Once you have created a breeded link you cannot create unbreeded links and vice versa. (You can,
however, have directed and undirected links in the same world, just not in the same breed)
Unlike with turtle breeds the singular breed name is required for link breeds, as many of the link
commands and reports use the singular name, such as -neighbor? .
The following primitives are also automatically available once you define a directed link breed: createstreet-from create-streets-from create-street-to create-streets-to in-street-neighbor? instreet-neighbors in-street-from my-in-streets my-out-streets out-street-neighbor? out-streetneighbors out-street-to
And the following are automatically available when you define an undirected link breed: createfriendship-with create-friendships-with friendship-neighbor? friendship-neighbors friendshipwith my-friendships
Multiple link breeds may declare the same -own variable, but a variable may not be shared between a
turtle breed and a link breed.
Just as with turtle breeds the order in which link breeds are declared defines the order in which the links
are drawn, so the friendships will always be on top of streets (if for some reason these breeds were in
the same model). You can also use -own to declare variables of each link breed
separately.
You can change the breed of a link with set breed. (However, you cannot change a breeded link to an
unbreeded one, to prevent having breeded and unbreeded links in the same world.)
ask one-of friendships [ set breed streets ]
ask one-of friendships [ set breed links ] ;; produces a runtime error
set-default-shape may
also be used with link breeds to associate it with a particular link shape.
Code Example: Link Breeds Example
Buttons
Buttons in the interface tab provide an easy way to control the model. Typically a model will have at
least a "setup" button, to set up the initial state of the world, and a "go" button to make the model run
continuously. Some models will have additional buttons that perform other actions.
A button contains some NetLogo code. That code is run when you press the button.
A button may be either a "once button", or a "forever button". You can control this by editing the button
and checking or unchecking the "Forever" checkbox. Once buttons run their code once, then stop and
pop back up. Forever buttons keep running their code over and over again.
A forever button stops if the user presses the button again to stop it. The button waits until the current
iteration has finished, then pops up.
A forever button can also be stopped from code. If the forever button directly calls a procedure, then
when that procedure stops, the button stops. (In a turtle or patch forever button, the button won't stop
until every turtle or patch stops -- a single turtle or patch doesn't have the power to stop the whole
button.)
Normally, a button is labeled with the code that it runs. For example, a button that says "go" on it usually
contains the code "go", which means "run the go procedure". (Procedures are defined in the Code tab;
see below.) But you can also edit a button and enter a "display name" for the button, which is a text that
appears on the button instead of the code. You might use this feature if you think the actual code would
be confusing to your users.
When you put code in a button, you must also specify which agents you want to run that code. You can
choose to have the observer run the code, or all turtles, or all patches, or all links. (If you want the code
to be run by only some turtles or some patches, you could make an observer button, and then have the
observer use the ask command to ask only some of the turtles or patches to do something.)
When you edit a button, you have the option to assign an "action key". This makes that key on the
keyboard behave just like a button press. If the button is a forever button, it will stay down until the key is
pressed again (or the button is clicked). Action keys are particularly useful for games or any model
where rapid triggering of buttons is needed.
Buttons take turns
More than one button can be pressed at a time. If this happens, the buttons "take turns", which means
that only one button runs at a time. Each button runs its code all the way through once while the other
buttons wait, then the next button gets its turn.
In the following examples, "setup" is a once button and "go" is a forever button.
Example #1: The user presses "setup", then presses "go" immediately, before the "setup" has popped
back up. Result: "setup" finishes before "go" starts.
Example #2: While the "go" button is down, the user presses "setup". Result: the "go" button finishes its
current iteration. Then the "setup" button runs. Then "go" starts running again.
Example #3: The user has two forever buttons down at the same time. Result: first one button runs its
code all the way through, then the other runs its code all the way through, and so on, alternating.
Note that if one button gets stuck in an infinite loop, then no other buttons will run.
Turtle, patch, and link forever buttons
There is a subtle difference between putting commands in a turtle, patch or link forever button, and
putting the same commands in an observer button that does ask turtles, ask patches or ask links. An
"ask" doesn't complete until all of the agents have finished running all of the commands in the "ask". So
the agents, as they all run the commands concurrently, can be out of sync with each other, but they all
sync up again at the end of the ask. The same isn't true of turtle, patch and link forever buttons. Since
ask was not used, each turtle or patch runs the given code over and over again, so they can become
(and remain) out of sync with each other.
At present, this capability is very rarely used in the models in our Models Library. A model that does use
the capability is the Termites model, in the Biology section of Sample Models. The "go" button is a turtle
forever button, so each termite proceeds independently of every other termite, and the observer is not
involved at all. This means that if, for example, you wanted to add ticks and/or a plot to the model, you
would need to add a second forever button (an observer forever button), and run both forever buttons at
the same time. Note also that a model like this cannot be used with BehaviorSpace.
Code Example: State Machine Example shows how Termites can be recoded in a tick-based
way, without using a turtle forever button.
At present, NetLogo has no way for one forever button to start another. Buttons are only started when
you press them.
Lists
In the simplest models, each variable holds only one piece of information, usually a number or a string.
Lists let you store multiple pieces of information in a single value by collecting that information in a list.
Each value in the list can be any type of value: a number, or a string, an agent or agentset, or even
another list.
Lists allow for the convenient packaging of information in NetLogo. If your agents carry out a repetitive
calculation on multiple variables, it might be easier to have a list variable, instead of multiple number
variables. Several primitives simplify the process of performing the same computation on each value in
a list.
The NetLogo Dictionary has a section that lists all of the list-related primitives.
Constant lists
You can make a list by simply putting the values you want in the list between brackets, like this: set
mylist [2 4 6 8]. Note that the individual values are separated by spaces. You can make lists that
contain numbers and strings this way, as well as lists within lists, for example [[2 4] [3 5]] .
The empty list is written by putting nothing between the brackets, like this: [].
Building lists on the fly
If you want to make a list in which the values are determined by reporters, as opposed to being a series
of constants, use the list reporter. The list reporter accepts two other reporters, runs them, and
reports the results as a list.
If I wanted a list to contain two random values, I might use the following code:
set random-list list (random 10) (random 20)
This will set random-list to a new list of two random integers each time it runs.
To make longer or shorter lists, you can use the list reporter with fewer or more than two inputs, but in
order to do so, you must enclose the entire call in parentheses, e.g.:
(list random 10)
(list random 10 random 20 random 30)
For more information, see Varying number of inputs.
Some kinds of lists are most easily built using the n-values reporter, which allows you to construct a list
of a specific length by repeatedly running a given reporter. You can make a list of the same value
repeated, or all the numbers in a range, or a lot of random numbers, or many other possibilities. See
dictionary entry for details and examples.
The of primitive lets you construct a list from an agentset. It reports a list containing each agent's value
for the given reporter. (The reporter could be a simple variable name, or a more complex expression -even a call to a procedure defined using to-report.) A common idiom is
max [...] of turtles
sum [...] of turtles
and so on.
You can combine two or more lists using the sentence reporter, which concatenates lists by combining
their contents into a single, larger list. Like list, sentence normally takes two inputs, but can accept any
number of inputs if the call is surrounded by parentheses.
Changing list items
Technically, lists can't be modified, but you can construct new lists based on old lists. If you want the
new list to replace the old list, use set. For example:
set mylist [2 7 5 Bob [3 0 -2]]
; mylist is now [2 7 5 Bob [3 0 -2]]
set mylist replace-item 2 mylist 10
; mylist is now [2 7 10 Bob [3 0 -2]]
The replace-item reporter takes three inputs. The first input specifies which item in the list is to be
changed. 0 means the first item, 1 means the second item, and so forth.
To add an item, say 42, to the end of a list, use the lput reporter. (fput adds an item to the beginning of
a list.)
set mylist lput 42 mylist
; mylist is now [2 7 10 Bob [3 0 -2] 42]
But what if you changed your mind? The but-last (bl for short) reporter reports all the list items but the
last.
set mylist but-last mylist
; mylist is now [2 7 10 Bob [3 0 -2]]
Suppose you want to get rid of item 0, the 2 at the beginning of the list.
set mylist but-first mylist
; mylist is now [7 10 Bob [3 0 -2]]
Suppose you wanted to change the third item that's nested inside item 3 from -2 to 9? The key is to
realize that the name that can be used to call the nested list [3 0 -2] is item 3 mylist . Then the replaceitem reporter can be nested to change the list-within-a-list. The parentheses are added for clarity.
set mylist (replace-item 3 mylist
(replace-item 2 (item 3 mylist) 9))
; mylist is now [7 10 Bob [3 0 9]]
Iterating over lists
If you want to do some operation on each item in a list in turn, the foreach command and the map
reporter may be helpful.
is used to run a command or commands on each item in a list. It takes an input list and a
command name or block of commands, like this:
foreach
foreach [1 2 3] show
=> 1
=> 2
=> 3
foreach [2 4 6]
[ n -> crt n
show (word "created " n " turtles") ]
=> created 2 turtles
=> created 4 turtles
=> created 6 turtles
In the block, the variable n holds the current value from the input list.
Here are some more examples of foreach :
foreach [1 2 3] [ steps -> ask turtles [ fd steps ] ]
;; turtles move forward 6 patches
foreach [true false true true] [ should-move? -> ask turtles [ if should-move? [ fd 1 ] ] ]
;; turtles move forward 3 patches
is similar to foreach , but it is a reporter. It takes an input list and a reporter name or reporter block.
Note that unlike foreach , the reporter comes first, like this:
map
show map round [1.2 2.2 2.7]
;; prints [1 2 3]
reports a list containing the results of applying the reporter to each item in the input list. Again, use
the variable named in the anonymous procedure (x in the examples below) to refer to the current item in
the list.
map
Here are a couple more examples of map:
show map [ x -> x < 0 ] [1 -1 3 4 -2 -10]
;; prints [false true false false true true]
show map [ x -> x * x ] [1 2 3]
;; prints [1 4 9]
Besides map and foreach , other primitives for processing whole lists in a configurable way include filter,
reduce, and sort-by .
These primitives aren't always the solution for every situation in which you want to operate on an entire
list. In some situations, you may need to use some other technique such as a loop using repeat or
while, or a recursive procedure.
The blocks of code we're giving to map and foreach in these examples are actually anonymous
procedures. Anonymous procedures are explained in more detail in Anonymous procedures, below.
Varying number of inputs
Some commands and reporters involving lists and strings may take a varying number of inputs. In these
cases, in order to pass them a number of inputs other than their default, the primitive and its inputs must
be surrounded by parentheses. Here are some examples:
show list 1 2
=> [1 2]
show (list 1 2 3 4)
=> [1 2 3 4]
show (list)
=> []
Note that each of these special primitives has a default number of inputs for which no parentheses are
required. The primitives which have this capability are list, word, sentence, map, foreach , run, and
runresult.
Lists of agents
Earlier, we said that agentsets are always in random order, a different random order every time. If you
need your agents to do something in a fixed order, you need to make a list of the agents instead.
There are two primitives that help you do this, sort and sort-by .
Both sort and sort-by can take an agentset as input. The result is always a new list, containing the
same agents as the agentset did, but in a particular order.
If you use sort on an agentset of turtles, the result is a list of turtles sorted in ascending order by who
number.
If you use sort on an agentset of patches, the result is a list of patches sorted left-to-right, top-to-bottom.
If you use sort on an agentset of links, the result is a list of links, sorted in ascending order first by end1
then by end2 any remaining ties are resolved by breed in the order they are declared in the Code tab.
If you need descending order instead, you can combine reverse with sort, for example reverse sort
turtles .
If you want your agents to be ordered by some other criterion than the standard ones sort uses, you'll
need to use sort-by instead.
Here's an example:
sort-by [ [a b] -> [size] of a < [size] of b ] turtles
This returns a list of turtles sorted in ascending order by their turtle variable size.
There's a common pattern to get a list of agents in a random order, using a combination of of and self,
in the rare case that you cannot just use ask:
[self] of my-agentset
Asking a list of agents
Once you have a list of agents, you might want to ask them each to do something. To do this, use the
foreach and ask commands in combination, like this:
foreach sort turtles [ the-turtle ->
ask the-turtle [
...
]
]
This will ask each turtle in ascending order by who number. Substitute "patches" for "turtles" to ask
patches in left-to-right, top-to-bottom order.
Note that you can't use ask directly on a list of turtles. ask only works with agentsets and single agents.
Performance of lists
The data structure underlying NetLogo's lists is a sophisticated tree-based data structure on which most
operations run in near-constant time. That includes fput, lput, butfirst, butlast , length, item, and
replace-item.
One exception to the fast-performance rule is that concatenating two lists with sentence requires
traversing and copying the whole second list. (This may be fixed in a future version.)
Technically, "near-constant time" is actually logarithmic time, proportional to the depth of the underlying
tree, but these trees have large nodes and a high branching factor, so they are never more than a few
levels deep. This means that changes can be made in at most a few steps. The trees are immutable, but
they share structure with each other, so the whole tree doesn't need to be copied to make a changed
version.
The actual data structure used is the immutable Vector class from the Scala collections library. These
are 32-wide hash array mapped tries, as implemented by Tiark Rompf, based in part on work by Phil
Bagwell and Rich Hickey.
Math
All numbers in NetLogo are stored internally as double precision floating point numbers, as defined in
the IEEE 754 standard. They are 64 bit numbers consisting of one sign bit, an 11-bit exponent, and a
52-bit mantissa. See the IEEE 754 standard for details.
An "integer" in NetLogo is simply a number that happens to have no fractional part. No distinction is
made between 3 and 3.0; they are the same number. (This is the same as how most people use
numbers in everyday contexts, but different from some programming languages. Some languages treat
integers and floating point numbers as distinct types.)
Integers are always printed by NetLogo without the trailing ".0":
show 1.5 + 1.5
observer: 3
If a number with a fractional part is supplied in a context where an integer is expected, the fractional part
is simply discarded. So for example, crt 3.5 creates three turtles; the extra 0.5 is ignored.
The range of integers is +/-9007199254740992 (2^53, about 9 quadrillion). Calculations that exceed this
range will not cause runtime errors, but precision will be lost when the least significant (binary) digits are
rounded off in order fit the number into 64 bits. With very large numbers, this rounding can result in
imprecise answers which may be surprising:
show 2 ^ 60 + 1 = 2 ^ 60
=> true
Calculations with smaller numbers can also produce surprising results if they involve fractional
quantities, since not all fractions can be precisely represented and roundoff may occur. For example:
show 1 / 6 + 1 / 6 + 1 / 6 + 1 / 6 + 1 / 6 + 1 / 6
=> 0.9999999999999999
show 1 / 9 + 1 / 9 + 1 / 9 + 1 / 9 + 1 / 9 + 1 / 9 + 1 / 9 + 1 / 9 + 1 / 9
=> 1.0000000000000002
Any operation which produces the special quantities "infinity" or "not a number" will cause a runtime
error.
Scientific notation
Very large or very small floating point numbers are displayed by NetLogo using "scientific notation".
Examples:
show 0.000000000001
=> 1.0E-12
show 50000000000000000000
=> 5.0E19
Numbers in scientific notation are distinguished by the presence of the letter E (for "exponent"). It means
"times ten to the power of", so for example, 1.0E-12 means 1.0 times 10 to the -12 power:
show 1.0 * 10 ^ -12
=> 1.0E-12
You can also use scientific notation yourself in NetLogo code:
show 3.0E6
=> 3000000
show 8.123456789E6
=> 8123456.789
show 8.123456789E7
=> 8.123456789E7
show 3.0E16
=> 3.0E16
show 8.0E-3
=> 0.0080
show 8.0E-4
=> 8.0E-4
These examples show that numbers with fractional parts are displayed using scientific notation if the
exponent is less than -3 or greater than 6. Numbers outside of NetLogo's integer range of 9007199254740992 to 9007199254740992 (+/-2^53) are also always shown in scientific notation:
show 2 ^ 60
=> 1.15292150460684698E18
When entering a number, the letter E may be either upper or lowercase. When printing a number,
NetLogo always uses an uppercase E:
show 4.5e20
=> 4.5E20
Floating point accuracy
Because numbers in NetLogo are subject to the limitations of how floating point numbers are
represented in binary, you may get answers that are slightly inaccurate. For example:
show 0.1 + 0.1 + 0.1
=> 0.30000000000000004
show cos 90
=> 6.123233995736766E-17
This is an inherent issue with floating point arithmetic; it occurs in all programming languages that use
floating point numbers.
If you are dealing with fixed precision quantities, for example dollars and cents, a common technique is
to use only integers (cents) internally, then divide by 100 to get a result in dollars for display.
If you must use floating point numbers, then in some situations you may need to replace a
straightforward equality test such as if x = 1 [ ... ] with a test that tolerates slight imprecision, for
example if abs (x - 1) < 0.0001 [ ... ] .
Also, the precision primitive is handy for rounding off numbers for display purposes. NetLogo monitors
round the numbers they display to a configurable number of decimal places, too.
Random numbers
The random numbers used by NetLogo are what is called "pseudo-random". (This is typical in computer
programming.) That means they appear random, but are in fact generated by a deterministic process.
"Deterministic" means that you get the same results every time, if you start with the same random
"seed". We'll explain in a minute what we mean by "seed".
In the context of scientific modeling, pseudo-random numbers are actually desirable. That's because it's
important that a scientific experiment be reproducible -- so anyone can try it themselves and get the
same result that you got. Since NetLogo uses pseudo-random numbers, the "experiments" that you do
with it can be reproduced by others.
Here's how it works. NetLogo's random number generator can be started with a certain seed value,
which must be an integer in the range -2147483648 to 2147483647. Once the generator has been
"seeded" with the random-seed command, it always generates the same sequence of random numbers
from then on. For example, if you run these commands:
random-seed 137
show random 100
show random 100
show random 100
You will always get the numbers 79, 89, and 61 in that order.
Note, however, that you're only guaranteed to get those same numbers if you're using the same version
of NetLogo. Sometimes when we make a new version of NetLogo the random number generator
changes. (Presently, we use a generator known as the Mersenne Twister.)
To create a number suitable for seeding the random number generator, use the new-seed reporter. newseed creates a seed, evenly distributed over the space of possible seeds, based on the current date and
time. It never reports the same seed twice in a row.
Code Example: Random Seed Example
If you don't set the random seed yourself, NetLogo sets it to a value based on the current date and time.
There is no way to find out what random seed it chose, so if you want your model run to be reproducible,
you must set the random seed yourself ahead of time.
The NetLogo primitives with "random" in their names (random, random-float, and so on) aren't the only
ones that use pseudo-random numbers. Many other operations also make random choices. For
example, agentsets are always in random order, one-of and n-of choose agents randomly, the sprout
command creates turtles with random colors and headings, and the downhill reporter chooses a random
patch when there's a tie. All of these random choices are governed by the random seed as well, so
model runs can be reproducible.
In addition to the uniformly distributed random integers and floating point numbers generated by random
and random-float , NetLogo also offers several other random distributions. See the dictionary entries for
random-normal , random-poisson , random-exponential , and random-gamma .
Auxiliary generator
Code run by buttons or from the command center uses the main random number generator.
Code in monitors uses an auxiliary random generator, so even if a monitor does a calculation that uses
random numbers, the outcome of the model is not affected. The same is true of code in sliders.
Local randomness
You may want to explicitly specify that a section of code does not affect the state of the main random
generator, so the outcome of the model is not affected. The with-local-randomness command is
provided for this purpose. See its entry in the NetLogo Dictionary for more information.
Turtle shapes
In NetLogo, turtle shapes are vector shapes. They are built up from basic geometric shapes; squares,
circles, and lines, rather than a grid of pixels. Vector shapes are fully scalable and rotatable. NetLogo
caches bitmap images of vector shapes size 1, 1.5, and 2 in order to speed up execution.
A turtle's shape is stored in its shape variable and can be set using the set command.
New turtles have a shape of "default". The set-default-shape primitive is useful for changing the default
turtle shape to a different shape, or having a different default turtle shape for each breed of turtle.
The shapes primitive reports a list of currently available turtle shapes in the model. This is useful if, for
example, you want to assign a random shape to a turtle:
ask turtles [ set shape one-of shapes ]
Use the Turtle Shapes Editor to create your own turtle shapes, or to add shapes to your model from our
shapes library, or to transfer shapes between models. For more information, see the Shapes Editor
section of this manual.
The thickness of the lines used to draw the vector shapes can be controlled by the __set-linethickness primitive.
Code Examples: Breeds and Shapes Example, Shape Animation Example
Link shapes
Link Shapes are similar to turtle shapes, only you use the Link Shape Editor to create and edit them.
Link shapes consist of between 0 and 3 lines which can have different patterns and a direction indicator
that is composed of the same elements as turtle shapes. Links also have a shape variable that can be
set to any link shape that is in the model. By default links have the "default" shape, though you can
change that using set-default-shape. The link-shapes reporter reports all the link shapes included in
the current model.
The thickness of the lines in the link shape is controlled by the thickness link variable.
View updates
The "view" in NetLogo lets you see the agents in your model on your computer's screen. As your agents
move and change, you see them moving and changing in the view.
Of course, you can't really see your agents directly. The view is a picture that NetLogo paints, showing
you how your agents look at a particular instant. Once that instant passes and your agents move and
change some more, that picture needs to be repainted to reflect the new state of the world. Repainting
the picture is called "updating" the view.
When does the view get updated? This section discusses how NetLogo decides when to update the
view, and how you can influence when it gets updated.
NetLogo offers two updates modes, "continuous" updates and "tick-based" updates. You can switch
between NetLogo's two view update modes using a popup menu at the top of the Interface tab.
Continuous updates are the default when you start up NetLogo or start a new model. Nearly every
model in our Models Library, however, uses tick-based updates.
Continuous updates are simplest, but tick-based updates give you more control over when and how
often updates happen.
It's important exactly when an update happens, because when updates happen determines what you
see on the screen. If an update comes at an unexpected time, you may see something unexpected -perhaps something confusing or misleading.
It's also important how often updates happen, because updates take time. The more time NetLogo
spends updating the view, the slower your model will run. With fewer updates, your model runs faster.
Continuous updates
Continuous updates are very simple. With continuous updates, NetLogo updates the view a certain
number of times per second -- by default, 30 times a second when the speed slider is in the default,
middle setting.
If you move the speed slider to a slower setting, NetLogo will update more than 30 times a second,
effectively slowing down the model. On a faster setting, NetLogo will update less than 30 times a
second. On the fastest setting, updates will be separated by several seconds.
At extremely slow settings, NetLogo will be updating so often that you will see your agents moving (or
changing color, etc.) one at a time.
If you need to temporarily shut off continuous updates, use the no-display command. The display
command turns updates back on, and also forces an immediate update (unless the user is fastforwarding the model using the speed slider).
Tick-based updates
As discussed above in the Tick Counter section, in many NetLogo models, time passes in discrete
steps, called "ticks". Typically, you want the view to update once per tick, between ticks. That's the
default behavior with tick-based updates.
If you want additional view updates, you can force an update using the display command. (The update
may be skipped if the user is fast-forwarding the model using the speed slider.)
You don't have to use the tick counter to use tick-based updates. If the tick counter never advances, the
view will update only when you use the display command.
If you move the speed slider to a fast enough setting, eventually NetLogo will skip some of the updates
that would ordinarily have happened. Moving the speed slider to a slower setting doesn't cause
additional updates; rather, it makes NetLogo pause after each update. The slower the setting, the longer
the pause.
Even under tick-based updates, the view also updates whenever a button in the interface pops up (both
once and forever buttons) and when a command entered in the Command Center finishes. So it's not
necessary to add the display command to once buttons that don't advance the tick counter. Many
forever buttons that don't advance the tick counter do need to use the display command. An example in
the Models Library is the Life model (under Computer Science -> Cellular Automata). The forever
buttons that let the user draw in the view use the display command so the user can see what they are
drawing, even though the tick counter is not advancing.
Choosing a mode
Advantages of tick-based updates over continuous updates include:
1. Consistent, predictable view update behavior which does not vary from computer to computer or
from run to run.
2. Continuous updates can confuse the user of your model by letting them see model states they
aren't supposed to see, which may be misleading.
3. Increased speed. Updating the view takes time, so if one update per tick is enough, then enforcing
there is only one update per tick will make your model faster.
4. Since setup buttons don't advance the tick counter, they are unaffected by the speed slider; this is
normally the desired behavior.
Nearly every model in our Models Library uses tick-based updates.
Continuous updates are occasionally useful for those rare models in which execution is not divided into
short, discrete phases. An example in the Models Library is Termites. (See also, however, the State
Machine Example model, which shows how to re-code Termites using ticks.)
Even for models that would normally be set to tick-based updates, it may be useful to switch to
continuous updates temporarily for debugging purposes. Seeing what's going on within a tick, instead of
only seeing the end result of a tick, could help with troubleshooting. After switching to continuous
updates, you may want to use the speed slider to slow the model down until you see your agents
moving one at a time. Don't forget to change back to tick-based updates when you are done, as the
choice of update mode is saved with the model.
Frame rate
One of the model settings in NetLogo's "Settings..." dialog is "Frame rate" which defaults to 30 frames
per second.
The frame rate setting affects both continuous updates and tick-based updates.
With continuous updates, the setting directly determines the frequency of updates.
With tick-based updates, the setting is a ceiling on how many updates per second you get. If the frame
rate is 30, then NetLogo will ensure that the model never runs faster than that when the speed slider is
in the default position. If any frame takes less than 1/30 of a second to compute and display, NetLogo
will pause and wait until the full 1/30 of a second has passed before continuing.
The frame rate settings lets you set what you consider to be a normal speed for your model. Then you,
or the user of your model, can use the speed slider to temporarily get a faster or slower speed.
Plotting
NetLogo's plotting features let you create plots to help you understand what's going on in your model.
Before you can plot, you need to create one or more plots in the Interface tab. For more information on
using and editing plots in the Interface tab, see the Interface Guide.
Plotting points
The two basic commands for actually plotting things are plot and plotxy.
With plot you need only specify the y value you want plotted. The x value will automatically be 0 for the
first point you plot, 1 for the second, and so on. (That's if the plot pen's "interval" is the default value of 1;
you can change the interval.)
The plot command is especially handy when you want your model to plot a new point at every time
step. Example:
plot count turtles
If you need to specify both the x and y values of the point you want plotted, then use plotxy instead.
This example assumes that a global variable called time exists:
plotxy time count-turtles
Plot commands
Each plot and its pens have setup and update code fields that may contain commands (usually
containing plot or plotxy). These commands are run automatically triggered by other commands in
NetLogo.
Plot setup commands and pen setup commands are run when the either reset-ticks or setup-plots
commands are run. If the stop command is run in the body of the plot setup commands then the pen
setup commands will not run.
Plot update commands and pen update commands are run when the either reset-ticks, tick or
update-plots commands are run. If the stop command is run in the body of the plot update commands
then the pen update commands will not run.
Here are the four commands that trigger plotting explained in more detail.
executes commands for one plot at a time. For each plot, the plot's setup commands
are executed. If the stop command is not encountered while running those commands, then each
of the plot's pens will have their setup code executed.
update-plots is very similar to setup-plots. For each plot, the plot's update commands are
setup-plots
executed. If the stop command is not encountered while running those commands, then each of
the plot's pens will have their update code executed.
tick is exactly the same as update-plots except that the tick counter is incremented before the
plot commands are executed.
reset-ticks first resets the tick counter to 0, and then does the equivalent of setup-plots followed
by update-plots .
A typical model will use reset-ticks and tick like so:
to setup
clear-all
...
reset-ticks
end
to go
...
tick
end
Note that in this example we plot from both the setup and go procedures (because reset-ticks runs plot
setup and plot update commands). We do this because we want our plot to include the initial state of the
system at the end of setup. We plot at the end of thego procedure, not the beginning, because we want
the plot always to be up to date after the go button stops.
Models that don't use ticks but still want to do plotting will instead use setup-plots and update-plots . In
the previous code, replace reset-ticks with setup-plots update-plots and replace tick with updateplots.
Code Example: Plotting Example
Other kinds of plots
By default, NetLogo plot pens plot in line mode, so that the points you plot are connected by a line.
If you want to move the pen without plotting, you can use the plot-pen-up command. After this
command is issued, the plot and plotxy commands move the pen but do not actually draw anything.
Once the pen is where you want it, use plot-pen-down to put the pen back down.
If you want to plot individual points instead of lines, or you want to draw bars instead of lines or points,
you need to change the plot pen's "mode". Three modes are available: line, bar, and point. Line is the
default mode.
Normally, you change a pen's mode by editing the plot. This changes the pen's default mode. It's also
possible to change the pen's mode temporarily using the set-plot-pen-mode command . That command
takes a number as input: 0 for line, 1 for bar, 2 for point.
Histograms
A histogram is a special kind of plot that measures how frequently certain values, or values in certain
ranges, occur in a collection of numbers that arise in your model.
For example, suppose the turtles in your model have an age variable. You could create a histogram of
the distribution of ages among your turtles with the histogram command, like this:
histogram [age] of turtles
The numbers you want to histogram don't have to come from an agentset; they could be any list of
numbers.
Note that using the histogram command doesn't automatically switch the current plot pen to bar mode. If
you want bars, you have to set the plot pen to bar mode yourself. (As we said before, you can change a
pen's default mode by editing the plot in the Interface tab.)
Like other types of plots, histograms can be set to auto scale. However, auto scaled histograms do not
automatically resize themselves horizontally like other plot types do. To set the range programmatically,
you can use the set-plot-x-range primitive.
The width of the bars in a histogram is controlled by the plot pen's interval. You can set a plot pen's
default interval by editing the plot in the Interface tab. You can also change the interval temporarily with
the set-plot-pen-interval command or the set-histogram-num-bars. If you use the latter command,
NetLogo will set the interval appropriately so as to fit the specified number of bars within the plot's
current x range.
Code Example: Histogram Example
Clearing and resetting
You can clear the current plot with the clear-plot command, or clear every plot in your model with
clear-all-plots. The clear-all command also clears all plots, in addition to clearing everything else in
your model.
If you want to remove only the points that a particular pen has drawn, use plot-pen-reset.
When a whole plot is cleared, or when a pen is reset, that doesn't just remove the data that has been
plotted. It also restores the plot or pen to its default settings, as they were specified in the Interface tab
when the plot was created or last edited. Therefore, the effects of such commands as set-plot-x-range
and set-plot-pen-color are only temporary.
Ranges and auto scaling
The default x and y ranges for a plot are fixed numbers, but they can be changed at setup time or as the
model runs.
To change the ranges at any time, use set-plot-x-range and set-plot-y-range. Or, you can let the
ranges grow automatically. Either way, when the plot is cleared the ranges will return to their default
values.
By default, all NetLogo plots have the auto scaling feature enabled. This means that if the model tries to
plot a point which is outside the current displayed range, the range of the plot will grow along one or
both axes so that the new point is visible. Histogram plots, however, do not auto scale horizontally.
In the hope that the ranges won't have to change every time a new point is added, when the ranges
grow they leave some extra room: 25% if growing horizontally, 10% if growing vertically.
If you want to turn off this feature, edit the plot and uncheck the Auto Scale? checkbox. At present, it is
not possible to enable or disable this feature only on one axis; it always applies to both axes.
Using a Legend
You can show the legend of a plot by checking the "Show legend" checkbox in the edit dialog. If you
don't want a particular pen to show up in the legend you can uncheck the "Show in Legend" checkbox
for that pen also in the advanced plot pen settings (the advanced plot pen settings can be opened by
clicking the pencil button for that pen in the plot pens table in the plot edit dialog).
Temporary plot pens
Most plots can get along with a fixed number of pens. But some plots have more complex needs; they
may need to have the number of pens vary depending on conditions. In such cases, you can make
"temporary" plot pens from code and then plot with them. These pens are called "temporary" because
they vanish when the plot is cleared (by the clear-plot, clear-all-plots, or clear-all commands).
To create a temporary plot pen, use the create-temporary-plot-pen command. Typically, this would be
done in the Code tab, but it is also possible to use this command from plot setup or plot update code (in
the edit dialog). By default, the new pen is down, is black in color, has an interval of 1, and plots in line
mode. Commands are available to change all of these settings; see the Plotting section of the NetLogo
Dictionary.
Before you can use the pen, you'll have to use the use the set-current-plot and set-current-plot-pen
commands. These are explained in the next section.
set-current-plot and set-current-plot-pen
Before NetLogo 5, it was not possible to put plot commands in the plot itself. All of the plot code was
written in the Code tab with the rest of the code. For backwards compatibility, and for temporary plot
pens, this is still supported. Models in previous versions of NetLogo (and those using temporary plot
pens) have to explicitly state which plot is the current plot with the set-current-plot command and
which pen is the current pen with the set-current-plot-pen command.
To set the current plot use the set-current-plot command with the name of the plot enclosed in double
quotes, like this:
set-current-plot "Distance vs. Time"
The name of the plot must be exactly as you typed it when you created the plot. Note that later if you
change the name of the plot, you'll also have to update the set-current-plot calls in your model to use
the new name. (Copy and paste can be helpful here.)
For a plot with multiple pens, you can manually specify which pen you want to plot with. If you don't
specify a pen, plotting will take place with the first pen in the plot. To plot with a different pen, the setcurrent-plot-pen command was used with the name of the pen enclosed in double quotes, like this:
set-current-plot-pen "distance"
Once the current pen is set, then commands like plot count turtles can be executed for that pen.
Older models with plots usually had their own do-plotting procedure that looked something like this:
to do-plotting
set-current-plot "populations"
set-current-plot-pen "sheep"
plot count sheep
set-current-plot-pen "wolves"
plot count wolves
set-current-plot "next plot"
...
end
Once again, this is no longer necessary in NetLogo 5, unless you are using temporary plot pens.
Conclusion
Not every aspect of NetLogo's plotting system has been explained here. See the Plotting section of the
NetLogo Dictionary for information on additional commands and reporters related to plotting.
Many of the Sample Models in the Models Library illustrate various advanced plotting techniques. Also
check out the following code examples:
Code Examples: Plot Axis Example, Plot Smoothing Example, Rolling Plot Example
Strings
Strings may contain any Unicode characters.
To input a constant string in NetLogo, surround it with double quotes.
The empty string is written by putting nothing between the quotes, like this: "".
Most of the list primitives work on strings as well:
but-first "string" => "tring"
but-last "string" => "strin"
empty? "" => true
empty? "string" => false
first "string" => "s"
item 2 "string" => "r"
last "string" => "g"
length "string" => 6
member? "s" "string" => true
member? "rin" "string" => true
member? "ron" "string" => false
position "s" "string" => 0
position "rin" "string" => 2
position "ron" "string" => false
remove "r" "string" => "sting"
remove "s" "strings" => "tring"
replace-item 3 "string" "o" => "strong"
reverse "string" => "gnirts"
A few primitives are specific to strings, such as is-string?, substring, and word:
is-string? "string" => true
is-string? 37 => false
substring "string" 2 5 => "rin"
word "tur" "tle" => "turtle"
Strings can be compared using the =, !=, <, >, <=, and >= operators.
If you need to embed a special character in a string, use the following escape sequences:
\n
\t
\"
\\
= newline
= tab
= double quote
= backslash
Output
This section is about output to the screen. Output to the screen can also be later saved to a file using
the export-output command. If you need a more flexible method of writing data to external files, see the
next section, File I/O.
The basic commands for generating output to the screen in NetLogo are print, show, type, and write.
These commands send their output to the Command Center.
For full details on these four commands, see their entries in the NetLogo Dictionary. Here is how they
are typically used:
print is useful in most situations.
show lets you see which agent is printing what.
type lets you print several things on the same line.
write lets you print values in a format which can be
read back in using file-read.
A NetLogo model may optionally have an "output area" in its Interface tab, separate from the Command
Center. To send output there instead of the Command Center, use the output-print , output-show,
output-type, and output-write commands.
The output area can be cleared with the clear-output command and saved to a file with export-output .
The contents of the output area will be saved by the export-world command. The import-world
command will clear the output area and set its contents to the value in imported world file. It should be
noted that large amounts of data being sent to the output area can increase the size of your exported
worlds.
If you use output-print , output-show, output-type, output-write , clear-output , or export-output in a
model which does not have a separate output area, then the commands apply to the output portion of
the Command Center.
File I/O
In NetLogo, there is a set of primitives that give you the power to interact with outside files. They all
begin with the prefix file-.
There are two main modes when dealing with files: reading and writing. The difference is the direction of
the flow of data. When you are reading in information from a file, data that is stored in the file flows into
your model. On the other hand, writing allows data to flow out of your model and into a file.
When working with files, always begin by using the primitive file-open. This specifies which file you will
be interacting with. None of the other primitives work unless you open a file first.
The next file- primitive you use dictates which mode the file will be in until the file is closed, reading or
writing. To switch modes, close and then reopen the file.
The reading primitives include file-read, file-read-line, file-read-characters, and file-at-end? Note
that the file must exist already before you can open it for reading.
Code Examples: File Input Example
The primitives for writing are similar to the primitives that print things in the Command Center, except
that the output gets saved to a file. They include file-print, file-show, file-type, and file-write. Note
that you can never "overwrite" data. In other words, if you attempt to write to a file with existing data, all
new data will be appended to the end of the file. (If you want to overwrite a file, use file-delete to
delete it, then open it for writing.)
Code Examples: File Output Example
When you are finished using a file, you can use the command file-close to end your session with the
file. If you wish to remove the file afterwards, use the primitive file-delete to delete it. To close multiple
opened files, one needs to first select the file by using file-open before closing it.
;; Open 3
file-open
file-open
file-open
files
"myfile1.txt"
"myfile2.txt"
"myfile3.txt"
;; Now close the 3 files
file-close
file-open "myfile2.txt"
file-close
file-open "myfile1.txt"
file-close
Or, if you know you just want to close every file, you can use file-close-all.
Two primitives worth noting are file-write and file-read . These primitives are designed to easily save
and retrieve NetLogo constants such as numbers, lists, booleans, and strings. file-write will always
output the variable in such a manner that file-read will be able to interpret it correctly.
file-open "myfile.txt" ;; Opening file for writing
ask turtles
[ file-write xcor file-write ycor ]
file-close
file-open "myfile.txt" ;; Opening file for reading
ask turtles
[ setxy file-read file-read ]
file-close
Code Examples: File Input Example and File Output Example
Letting the user choose
The user-directory, user-file, and user-new-file primitives are useful when you want the user to
choose a file or directory for your code to operate on.
Movies
This section describes how to capture an ".mp4" movie of a NetLogo model.
First, use the vid:start-recorder command to start the video recorder.
To add a frame to your movie, use either vid:record-view or vid:record-interface, depending on
whether you want the movie to show just the current view, or the entire Interface tab. In a single movie,
the resolution will be one of the following:
the resolution specified in the call tovid:start-recorder width height if you specified the
resolution. These are optional parameters.
The resolution of the view if you did not specify a resolution in the call to vid:start-recorder and
call vid:record-view before calling vid:record-interface
The resolution of the interface if you did not specify a resolution in the call to vid:start-recorder
and call vid:record-interface before calling vid:record-view
Note that if the resolution of a recorded image doesn't match the resolution of the recording it will be
scaled to fit which can result in images which look blurry or out-of-focus.
When you're done adding frames, use vid:save-recording. The filename you provide should end with
.mp4, the extension for MP4-encoded movies (playable in QuickTime and other programs).
;; export a 30 frame movie of the view
extensions [vid]
;...
setup
vid:start-recorder
vid:record-view ;; show the initial state
repeat 30
[ go
vid:record-view ]
vid:save-recording "out.mp4"
A movie will play back at 25 frames per second. To make the movie playback faster or slower, consider
using a video postprocessing tool.
To check whether or not you are recording, call vid:recorder-status, which reports a string that
describes the state of the current recorder.
To throw away the movie currently being recorded, call vid:reset-recorder.
Code Example: Movie Example
Movies generated when running headless, or by background runs in a parallel BehaviorSpace
experiment may use only vid:record-view primitive. Movies generated in NetLogo GUI may also use
vid:record-interface and vid:record-source .
NetLogo movies are exported as H.264-encoded MP4 files. To play an MP4 movie, you can use the VLC
Player, a free download from the VideoLAN organization.
Movies can take up a lot of disk space. You will probably want to compress your movies with third-party
software. The software may give you a choice of different kinds of compression. Some kinds of
compression are lossless, while others are lossy. "Lossy" means that in order to make the files smaller,
some of the detail in the movie is lost. Depending on the nature of your model, you may want to avoid
using lossy compression, for example if the view contains fine pixel-level detail.
Perspective
The 2D and the 3D view show the world from the perspective of the observer. By default the observer is
looking down on the world from the positive z-axis at the origin. You can change the perspective of the
observer by using the follow, ride and watch observer commands and follow-me , ride-me and watch-me
turtle commands. When in follow or ride mode the observer moves with the subject agent around the
world. The difference between follow and ride is only visible in the 3D view. In the 3D view the user can
change the distance behind the agent using the mouse. When the observer is following at zero distance
from the agent it is actually riding the agent. When the observer is in watch mode it tracks the
movements of one turtle without moving. In both views you will see a spotlight appear on the subject and
in the 3D view the observer will turn to face the subject. To determine which agent is the focus you can
use the subject reporter.
Code Example: Perspective Example
Drawing
The drawing is a layer where turtles can make visible marks.
In the view, the drawing appears on top of the patches but underneath the turtles. Initially, the drawing is
empty and transparent.
You can see the drawing, but the turtles (and patches) can't. They can't sense the drawing or react to it.
The drawing is just for people to look at.
Turtles can draw and erase lines in the drawing using the pen-down and pen-erase commands. When a
turtle's pen is down (or erasing), the turtle draws (or erases) a line behind it whenever it moves. The
lines are the same color as the turtle. To stop drawing (or erasing), use pen-up.
Lines drawn by turtles are normally one pixel thick. If you want a different thickness, set the pen-size
turtle variable to a different number before drawing (or erasing). In new turtles, the variable is set to 1.
Lines made when a turtle moves in a way that doesn't fix a direction, such as with setxy or move-to , the
shortest path line that obeys the topology will be drawn.
Here's some turtles which have made a drawing over a grid of randomly shaded patches. Notice how
the turtles cover the lines and the lines cover the patch colors. The pen-size used here was 2:
The stamp command lets a turtle leave an image of itself behind in the drawing and stamp-erase lets it
remove the pixels below it in the drawing.
To erase the whole drawing, use the observer commmand clear-drawing . (You can also use clear-all,
which clears everything else too.)
Importing an image
The observer command import-drawing command allows you to import an image file from disk into the
drawing.
is useful only for providing a backdrop for people to look at. If you want turtles and
patches to react to the image, you should use import-pcolors or import-pcolors-rgb instead.
import-drawing
Comparison to other Logos
Drawing works somewhat differently in NetLogo than some other Logos.
Notable differences include:
New turtles' pens are up, not down.
Instead of using a fence command to confine the turtle inside boundaries, in NetLogo you edit the
world and turn wrapping off.
There is no screen-color , bgcolor , or setbg. You can make a solid background by coloring the
patches, e.g. ask patches [ set pcolor blue ] .
Drawing features not supported by NetLogo:
There is no window command. This is used in some other Logos to let the turtle roam over an
infinite plane.
There is no flood or fill command to fill an enclosed area with color.
Topology
The way the world of patches is connected can change. By default the world is a torus which means it
isn't bounded, but "wraps" -- so when a turtle moves past the edge of the world, it disappears and
reappears on the opposite edge and every patch has the same number of "neighbor" patches. If you're a
patch on the edge of the world, some of your "neighbors" are on the opposite edge.
However, you can change the wrap settings with the Settings button. If wrapping is not allowed in a
given direction then in that direction (x or y) the world is bounded. Patches along that boundary will have
fewer than 8 neighbors and turtles will not move beyond the edge of the world.
The topology of the NetLogo world has four potential values, torus, box, vertical cylinder, or horizontal
cylinder. The topology is controlled by enabling or disabling wrapping in the x or y directions. The default
world is a torus.
A torus wraps in both directions, meaning that the top and bottom edges of the world are connected and
the left and right edges are connected. So if a turtle moves beyond the right edge of the world it appears
again on the left and the same for the top and bottom.
A box does not wrap in either direction. The world is bounded so turtles that try to move off the edge of
the world cannot. Note that the patches around edge of the world have fewer than eight neighbors; the
corners have three and the rest have five.
Horizontal and vertical cylinders wrap in one direction but not the other. A horizontal cylinder wraps
vertically, so the top of the world is connected to the bottom. but the left and right edges are bounded. A
vertical cylinder is the opposite; it wraps horizontally so the left and right edges are connected, but the
top and bottom edges are bounded.
Code Example: Neighbors Example
When coordinates wrap, turtles and links wrap visually in the view, too. If a turtle shape or link extends
past an edge, part of it will appear at the other edge. (Turtles themselves are points that take up no
space, so they cannot be on both sides of the world at once, but in the view, they appear to take up
space because they have a shape.)
Wrapping also affects how the view looks when you are following a turtle. On a torus, wherever the turtle
goes, you will always see the whole world around it:
Whereas in a box or cylinder the world has edges, so the areas past those edges show up in the view as
gray:
Code Example: Termites Perspective Demo (torus), Ants Perspective Demo (box)
The topology settings also control the behavior of the distance(xy), in-radius, in-cone, face(xy), and
towards(xy) primitives. The topology controls whether the primitives wrap or not. They always use the
shortest path allowed by the topology. For example, the distance from the center of the patches in the
bottom right corner (min-pxcor, min-pycor) and the upper left corner (max-pxcor, max-pycor) will be as
follows for each topology given that the min and max pxcor and pycor are +/-2:
Torus - sqrt(2) ~ 1.414 (this will be the same for all world sizes since the patches are directly
diagonal to each other in a torus.)
Box - sqrt(world-width^2 + world-height^2) ~ 7.07
Vertical Cylinder - sqrt(world-height^2 + 1) ~ 5.099
Horizontal Cylinder - sqrt(world-width^2 + 1) ~ 5.099
All the other primitives will act similarly to distance. If you formerly used -nowrap primitives in your model
we recommend removing them and changing the topology of the world instead.
If your model has turtles that move around you'll need to think about what happens to them when they
reach the edge of the world, if the topology you're using has some non-wrapping edges. There are a few
common options: the turtle is reflected back into the world (either systematically or randomly), the turtle
exits the system (dies), or the turtle is hidden. It is no longer necessary to check the bounds using turtle
coordinates, instead we can just ask NetLogo if a turtle is at the edge of the world. There are a couple
ways of doing this, the simplest is to use the can-move? primitive.
if not can-move? distance [ rt 180 ]
can-move? merely returns true if the position distance in front of the turtle is inside the NetLogo world,
false otherwise. In this case, if the turtle is at the edge of the world it simple goes back the way it came.
You can also use patch-ahead 1 != nobody in place of can-move?. If you need to do something smarter
that simply turning around it may be useful to use patch-at with dx and dy.
if patch-at dx 0 = nobody [
set heading (- heading)
]
if patch-at 0 dy = nobody [
set heading (180 - heading)
]
This tests whether the turtle is hitting a horizontal or vertical wall and bounces off that wall.
In some models if a turtle can't move forward it simply dies (exits the system, like in Conductor or
Mousetraps).
if not can-move? distance[ die ]
If you are moving turtles using setxy rather than forward you should test to make sure the patch you are
about to move to exists since setxy throws a runtime error if it is given coordinates outside the world.
This is a common situation when the model is simulating an infinite plane and turtles outside the view
should simply be hidden.
let new-x new-value-of-xcor
let new-y new-value-of-ycor
ifelse patch-at
[ hide-turtle
[ setxy new-x
show-turtle
(new-x - xcor) (new-y - ycor) = nobody
]
new-y
]
Several models in the Models Library use this technique, Gravitation, N-Bodies, and Electrostatics are
good examples.
The diffuse and diffuse4 commands behave correctly in all topologies. Each patch diffuses and equal
amount of the diffuse variable to each of its neighbors, if it has fewer than 8 neighbors (or 4 if you are
using diffuse4), the remainder stays on the diffusing patch. This means that the overall sum of patchvariable across the world remains constant. However, if you want the diffuse matter to still fall off the
edges of the world as it would on an infinite plane you still need to clear the edges each step as in the
Diffuse Off Edges Example.
Links
A link is an agent that connects two turtles. These turtles are sometimes also called nodes.
The link is always drawn as a line between the two turtles. Links do not have a location as turtles do,
they are not considered to be on any patch and you cannot find the distance from a link to another point.
There are two link designations: undirected and directed. A directed link is out of, or from, one node and
into, or to, another node. The relationship of a parent to a child could be modeled as a directed link. An
undirected link appears the same to both nodes, each node has a link with another node. The
relationship between spouses, or siblings, could be modeled as an undirected link.
There is a global agentset of all links, just as with turtles and patches. You can create undirected links
using the create-link-with and create-links-with commands; and directed links using the createlink-to , create-links-to , create-link-from, and create-links-from commands. Once the first link has
been created directed or undirected, all unbreeded links must match (links also support breeds, much
like turtles, which will be discussed shortly); it's impossible to have two unbreeded links where one is
directed and the other is undirected. A runtime error occurs if you try to do it. (If all unbreeded links die,
then you can create links of that breed that are different in designation from the previous links.)
In general, link primitive names indicate what kind of links they deal with:
Primitives that have "out" in their name utilize outgoing and undirected links. You can think of these
as "the links I can use to get from the current node to other nodes." In general, these are probably
the primitives you want to use.
Primitives that have "in" in their name utilize incoming and undirected links. You can think of these
as "the links I can use to get to the current node from other nodes."
Primtives that do not specify "in" or "out", or have "with" in their name utilize all links, both
undirected and directed, incoming and outgoing.
A link's end1 and end2 variables contain the two turtles the link connects. If the link is directed, it goes
from end1 to end2. If the link is undirected, end1 is always the older of the two turtles, that is, the turtle
with the smaller who number.
Link breeds, like turtle breeds, allow you to define different types of links in your model. Link breeds
must either be directed or undirected, unlike unbreeded links this is defined at compile time rather than
run time. You declare link breeds using the keywords undirected-link-breed and directed-link-breed.
Breeded links can be created using the commands create--with and create--with for
undirected breeds and the commands create--to , create--to , create--from,
and create--from for directed links.
There cannot be more than one undirected link of the same breed (or more than one unbreeded
undirected link) between a pair of agents, nor more than one directed link of the same breed in the
same direction between a pair of agents. You can have two directed links of the same breed (or two
unbreeded directed links) between a pair if they are in opposite directions.
Layouts
As part of our network support we have also added several different primitives that will help you to
visualize the networks. The simplest is layout-circle which evenly spaces the agents around the center
of the world given a radius.
is a good layout if you have something like a tree structure, though even if there are some
cycles in the tree it will still work, though as there are more and more cycles it will probably not look as
good. layout-radial takes a root agent to be the central node places it at (0,0) and arranges the nodes
connected to it in a concentric pattern. Nodes one degree away from the root will be arranged in a
circular pattern around the central node and the next level around those nodes and so on. layoutradial will attempt to account for asymmetrical graphs and give more space to branches that are wider.
layout-radial also takes a breed as an input so you use one breed of links to layout the network and
not another.
layout-radial
Given a set of anchor nodes layout-tutte places all the other nodes at the center of mass of the nodes
it is linked to. The anchor set is automatically arranged in a circle layout with a user defined radius and
the other nodes will converge into place (this of course means that you may have to run it several times
before the layout is stable.)
is useful for many kinds of networks. The drawback is that is relatively slow since it takes
many iterations to converge. In this layout the links act as springs that pull the nodes they connect
toward each other and the nodes repel each other. The strength of the forces is controlled by inputs to
the primitives. These inputs will always have a value between 0 and 1; keep in mind that very small
changes can still affect the appearance of the network. The springs also have a length (in patch units),
layout-spring
however, because of all the forces involved the nodes will not end up exactly that distance from each
other.
Code Examples:Network Example, Network Import Example, Giant Component, Small
Worlds, Preferential Attachment
Anonymous procedures
Anonymous procedures let you store code to be run later. Just like regular NetLogo procedures, an
anonymous procedures can be either a command (anonymous command) or a reporter (anonymous
reporter).
Anonymous procedures are values, which means they may be passed as input, reported as a result, or
stored in a variable.
An anonymous procedure might be run once, multiple times, or not at all.
In other programming languages anonymous procedures are known as first-class functions, closures, or
lambda.
Anonymous procedure primitives
Primitives specific to anonymous procedures are ->, is-anonymous-command?, and is-anonymousreporter?.
The -> creates an anonymous procedure. The anonymous procedure it reports might be a command or
a reporter, depending on what kind of block you pass it. For example [ -> fd 1 ] reports an
anonymous command, because fd is a command, while [ -> count turtles ] reports an anonymous
reporter, because count is a reporter.
These primitives require anonymous procedures as input: foreach , map, reduce, filter, n-values , sortby . When calling these primitives, using an -> is optional if your anonymous procedure takes no
arguments. For example one may write simply foreach mylist [ print ] instead of foreach mylist [
[x] -> print x ], though the latter is also accepted. Additionally, while brackets around argument
names are required for anonymous procedures of two or more arguments, they may be omitted for
anonymous procedures of one or zero arguments. So foreach mylist [ x -> print x ] is equivalent
to foreach mylist [ [x] -> print x ] .
Note: brackets around arguments were always required in NetLogo 6.0.0. If you copy and paste code
into NetLogo 6.0.0 using anonymous procedures with unbracketed arguments, the code will not compile
until you have added the brackets.
The run command accepts anonymous commands as well as strings.
The runresult reporter accepts anonymous reporters as well as strings.
and runresult allow passing inputs to an anonymous procedure. As with all primitives accepting
varying number of inputs, the whole call must be surrounded with parentheses, so for example (run myanonymous-command 5) or (runresult my-anonymous-reporter "foo" 2) . When not passing input, no
parentheses are required.
run
Anonymous procedure inputs
An anonymous procedure may take zero or more inputs. The inputs are referenced the variables
declared before the arrow. For instance, in the anonymous reporter [ [a b] -> a + b ] , a and b are
inputs.
Anonymous procedures and strings
Creating and running anonymous procedures is fast. To use run or runresult on a new string for the first
time is about 100x slower than running an anonymous procedure. Modelers should normally use
anonymous procedures instead of running strings, except when running strings entered by the user.
Concise syntax
Simple uses of foreach , map, reduce, filter, n-values , and sort-by can be written with an especially
concise syntax. You can write:
map abs [1 -2 3 -4] => [1 2 3 4]
reduce + [1 2 3 4] => 10
filter is-number? [1 "x" 3] => [1 3]
foreach [1 2 3 4] print
In older NetLogo versions (4 and earlier), these had to be written:
map [abs ?] [1 -2 3 -4] => [1 2 3 4]
reduce [?1 + ?2] [1 2 3 4] => 10
filter [is-number? ?] [1 "x" 3] => [1 3]
foreach [1 2 3 4] [ print ? ]
Anonymous procedures as closures
Anonymous procedures are "closures"; that means they capture or "close over" the bindings (not just the
current values) of local variables and procedure inputs. They do not capture agent variables and do not
capture the identity (or even the agent type) of the current agent.
Nonlocal exits
The stop and report commands exit from the dynamically enclosing procedure, not the enclosing
anonymous procedure. (This is backward-compatible with older NetLogo versions.)
Anonymous procedures and extensions
The extensions API supports writing primitives that accept anonymous procedures as input. Write us for
sample code.
Limitations
We hope to address at least some of the following limitations in future NetLogo versions:
does not support anonymous procedures.
Anonymous procedures can't be variadic (accept a varying number of inputs).
Anonymous reporters can't contain commands, only a single reporter expression. So for example
you must use ifelse-value not if, and you don't use report at all. If your code is too complex to
be written as one reporter, you'll need to move the code to a separate reporter procedure, and
then call that procedure from your anonymous reporter, passing it any needed inputs.
Anonymous procedures are not interchangeable with command blocks and reporter blocks. Only
the primitives listed above accept anonymous procedures as input. Control primitives such as
ifelse and while and agent primitives such as of and with don't accept anonymous procedures.
So for example if I have an anonymous reporter let r [ -> if random 2 == 0 ] and two
anonymous commands let c1 [ -> tick ] and let c2 [ -> stop ] , I can't write ifelse r c1 c2,
I must write ifelse runresult r [ run c1 ] [ run c2 ].
The concise syntax where -> may be omitted is only available to primitives and extension
primitives, not ordinary procedures. So for example if I have a procedure p that accepts an
anonymous procedure as input, it must be called as e.g. p [ -> ... ] not p [ ... ] .
import-world
Code example
Code Example: State Machine Example
Ask-Concurrent
NOTE: The following information is included only for backwards compatibility. We don't recommend
using the ask-concurrent primitive at all in new models.
In very old versions of NetLogo, ask had simulated concurrent behavior by default. Since NetLogo 4.0
(2007), ask is serial, that is, the agents run the commands inside the ask one at a time.
The following information describes the behavior of the ask-concurrent command, which behaves the
way the old ask behaved.
produces simulated concurrency via a mechanism of turn-taking. The first agent takes a
turn, then the second agent takes a turn, and so on until every agent in the asked agentset has had a
turn. Then we go back to the first agent. This continues until all of the agents have finished running all of
the commands.
ask-concurrent
An agent's "turn" ends when it performs an action that affects the state of the world, such as moving, or
creating a turtle, or changing the value of a global, turtle, patch, or link variable. (Setting a local variable
doesn't count.)
The forward (fd) and back (bk) commands are treated specially. When used inside ask-concurrent,
these commands can take multiple turns to execute. During its turn, the turtle can only move by one
step. Thus, for example, fd 20 is equivalent to repeat 20 [ fd 1 ] , where the turtle's turn ends after
each run of fd. If the distance specified isn't an integer, the last fraction of step takes a full turn. So for
example fd 20.3 is equivalent to repeat 20 [ fd 1 ] fd 0.3.
The jump command always takes exactly one turn, regardless of distance.
To understand the difference between ask and ask-concurrent, consider the following two commands:
ask turtles [ fd 5 ]
ask-concurrent turtles [ fd 5 ]
With ask, the first turtle takes five steps forward, then the second turtle takes five steps forward, and so
on.
With ask-concurrent, all of the turtles take one step forward. Then they all take a second step, and so
on. Thus, the latter command is equivalent to:
repeat 5 [ ask turtles [ fd 1 ] ]
Code Example: Ask-Concurrent Example shows the difference between ask and askconcurrent.
The behavior of ask-concurrent cannot always be so simply reproduced using ask, as in this example.
Consider this command:
ask-concurrent turtles [ fd random 10 ]
In order to get the same behavior using ask, we would have to write:
turtles-own [steps]
ask turtles [ set steps random 10 ]
while [any? turtles with [steps > 0]] [
ask turtles with [steps > 0] [
fd 1
set steps steps - 1
]
]
To prolong an agent's "turn", use the without-interruption command. (The command blocks inside
some commands, such as create-turtles and hatch, have an implied without-interruption around
them.)
Note that the behavior of ask-concurrent is completely deterministic. Given the same code and the
same initial conditions, the same thing will always happen (if you are using the same version of NetLogo
and begin your model run with the same random seed).
In general, we suggest you not use ask-concurrent at all. If you do, we suggest you write your model so
that it does not depend on the exact details of how ask-concurrent works. We make no guarantees that
its semantics will remain the same in future versions of NetLogo, or that it will continue to be supported
at all.
User Interaction Primitives
NetLogo features several primitives which allow a model to interact with the user. These primitives
include user-directory, user-file, user-new-file, user-input, user-message, user-one-of, and user-yes-orno?.
These primitives differ in precisely what interaction they take with the user. user-directory, user-file,
and user-new-file are all reporters which prompt the user to select an item from the file system and
report the path of the selected item to NetLogo. user-yes-or-no?, user-one-of, and user-input all
prompt the user to provide input in the form of text or a selection. user-message simply presents a
message to the user.
Note that all active forever buttons will pause when one of these primitives is used and will resume only
when the user completes the interaction with the button.
What does "Halt" mean?
The primitives which prompt the user for input, as well as user-message all provide a "Halt" button. The
effect of this button is the same for all of these primitives - it halts the model. When the model is halted
all running code is stopped, including buttons and the command center. Since halting stops code in the
middle of whatever it happened to be doing at the time it was halted, you may see strange results if you
continue to run the model after a halt without setting it up again.
Tie
Tie connects two turtles so that the movement of one turtles affects the location and heading of another.
Tie is a property of links so there must be a link between two turtles to create a tie relationship.
When a link's tie-mode is set to "fixed" or "free" end1 and end2 are tied together. If the link is directed end1
is the "root agent" and end2 is the "leaf agent". That is when end1 moves (using fd, jump, setxy, etc.) end2
also moves the same distance and direction. However when end2 moves it does not affect end1.
If the link is undirected it is a reciprocal tie relationship, meaning, if either turtle moves the other turtle
will also move. So depending on which turtle is moving either turtle can be considered the root or the
leaf. The root turtle is always the turtle that initiates the movement.
When the root turtle turns right or left, the leaf turtle rotates around the root turtle the same amount as if
a stiff were attaching the turtles. When tie-mode is set to "fixed" the heading of the leaf turtle changes by
the same amount. If the tie-mode is set to "free" the heading of the leaf turtle is unchanged.
The tie-mode of a link can be set to "fixed" using the tie command and set to "none" (meaning the
turtles are no longer tied) using untie to set the mode to "free" you need to: set tie-mode "free".
Code Example: Tie System Example
Multiple source files
The __includes keyword allows you to use multiple source files in a single NetLogo model.
The keyword begins with two underscores to indicate that the feature is experimental and may change
in future NetLogo releases.
When you open a model that uses the __includes keyword, or if you add it to the top of a model and hit
the Check button, the includes menu will appear in the toolbar. From the includes menu you can select
from the files included in this model.
When you open included files they appear in additional tabs. See the Interface Guide for more details.
You can have anything in external source files (.nls) that you would normally put in the Code tab:
globals , breed, turtles-own, patches-own, breeds-own, procedure definitions, etc. Note though that these
declarations all share the same namespace. That is, if you declare a global my-global in the Code tab
you cannot declare a global (or anything else) with the name my-global in any file that is included in the
model. my-global will be accessible from all the included files. The same would be true if my-global were
declared in one of the included files.
Syntax
Colors
In the Code tab and elsewhere in the NetLogo user interface, program code is color-coded by the
following scheme:
Keywords are green
Constants are orange
Comments are gray
Primitive commands are blue
Primitive reporters are purple
Everything else is black
Notice
The remainder of this section contains technical terminology which will be unfamiliar to some readers.
Keywords
The only keywords in the language are globals , breed, turtles-own, patches-own, to, to-report, and end,
plus extensions and the experimental __includes keyword. (Built-in primitive names may not be
shadowed or redefined, so they are effectively a kind of keyword as well.)
Identifiers
All primitives, global and agent variable names, and procedure names share a single global caseinsensitive namespace; local names (let variables and the names of procedure inputs) may not shadow
global names or each other. Identifiers may contain any Unicode letter or digit and the following ASCII
characters:
.?=*!<>:#+/%$_^'&-
Some primitive names begin with two underscores to indicate that they are experimental and are
especially likely to change or be removed in future NetLogo releases.
Scope
NetLogo is lexically scoped. Local variables (including inputs to procedures) are accessible within the
block of commands in which they are declared, but not accessible by procedures called by those
commands.
Comments
The semicolon character introduces a comment, which lasts until the end of the line. There is no multiline comment syntax.
Structure
A program consists of optional declarations (globals , breed, turtles-own, patches-own, -own,
extensions) in any order, followed by zero or more procedure definitions. Multiple breeds may be
declared with separate breed declarations; the other declarations may appear once only.
Every procedure definition begins with to or to-report, the procedure name, and an optional bracketed
list of input names. Every procedure definition ends with end. In between are zero or more commands.
Commands and reporters
Commands take zero or more inputs; the inputs are reporters, which may also take zero or more inputs.
No punctuation separates or terminates commands; no punctuation separates inputs. Identifiers must be
separated by whitespace or by parentheses or square brackets. (So for example, a+b is a single
identifier, but a(b[c]d)e contains five identifiers.)
All commands are prefix. All user-defined reporters are prefix. Most primitive reporters are prefix, but
some (arithmetic operators, boolean operators, and some agentset operators like with and in-points) are
infix.
All commands and reporters, both primitive and user-defined, take a fixed number of inputs by default.
(That's why the language can be parsed though there is no punctuation to separate or terminate
commands and/or inputs.) Some primitives are variadic, that is, may optionally take a different number
of inputs than the default; parentheses are used to indicate this, e.g. (list 1 2 3) (since the list
primitive only takes two inputs by default). Parentheses are also used to override the default operator
precedence, e.g. (1 + 2) * 3 , as in other programming languages.
Sometimes an input to a primitive is a command block (zero or more commands inside square brackets)
or a reporter block (a single reporter expression inside square brackets). User-defined procedures may
not take a command or reporter block as input.
Operator precedences are as follows, high to low:
with, at-points, in-radius, in-cone
(all other primitives and user-defined procedures)
^
*, /, mod
+, <, >, <= , >=
=, !=
and, or , xor
Compared to other Logos
There is no agreed-upon standard definition of Logo; it is a loose family of languages. We believe that
NetLogo has enough in common with other Logos to earn the Logo name. Still, NetLogo differs in some
respects from most other Logos. The most important differences are as follows.
Surface differences
The precedence of mathematical operators is different. Infix math operators (like +, *, etc.) have
lower precedence than reporters with names. For example, in many Logos, if you write sin x + 1 ,
it will be interpreted as sin (x + 1) . NetLogo, on the other hand, interprets it the way most other
programming languages would, and the way the same expression would be interpreted in
standard mathematical notation, namely as (sin x) + 1.
The and and or reporters are special forms, not ordinary functions, and they "short circuit", that is,
they only evaluate their second input if necessary.
Procedures can only be defined in the Code tab, not interactively in the Command Center.
Reporter procedures, that is, procedures that "report" (return) a value, must be defined with toreport instead of to . The command to report a value from a reporter procedure is report, not
output.
When defining a procedure, the inputs to the procedure must be enclosed in square brackets, e.g.
to square [x] .
Variable names are always used without any punctuation: always foo, never :foo or "foo. (To
make this work, instead of a make command taking a quoted argument we supply a set special
form which does not evaluate its first input.) As a result, procedures and variables occupy a single
shared namespace.
The last three differences are illustrated in the following procedure definitions:
most Logos
to square :x
output :x * :x
end
NetLogo
to-report square [x]
report x * x
end
Deeper differences
NetLogo's local variables and inputs to procedures are lexically scoped, not dynamically scoped.
NetLogo has no "word" data type (what Lisp calls "symbols"). Eventually, we may add one, but
since it is seldom requested, it may be that the need doesn't arise much in agent-based modeling.
We do have strings. In most situations where traditional Logo would use words, we simply use
strings instead. For example in Logo you could write [see spot run] (a list of words), but in
NetLogo you must write "see spot run" (a string) or ["see" "spot" "run"] (a list of strings)
instead.
NetLogo's run command works on anonymous procedures and strings, not lists (since we have no
"word" data type), and does not permit the definition or redefinition of procedures.
Control structures such as if and while are special forms, not ordinary functions. You can't define
your own special forms, so you can't define your own control structures. (You can do something
similar using anonymous procedures, but you must use the ->, run, and runresult primitives for
that, you cannot make them implicit.)
Anonymous procedures (aka function values or lambda) are true lexically-scoped closures. This
feature is available in NetLogo and in modern Lisps, but not in standard Logo.
Of course, the NetLogo language also contains other features not found in most Logos, most importantly
agents and agentsets.
Transition Guide
Many models created in earlier versions of NetLogo also work in NetLogo 5.0. However,
some models will need changes. If an old model isn't working, this section of the User Manual
may be able to help you.
What issues may arise depends on what version of NetLogo the model was created with.
This guide only covers changes most likely to cause issues for users. See the Release notes
for more complete details on differences between versions.
Changes for NetLogo 6.0
Changes for NetLogo 5.2
Changes for NetLogo 5.0
Changes for NetLogo 4.1
Changes for NetLogo 4.0
Changes for NetLogo 3.1
Changes for NetLogo 6.0
Tasks replaced by Anonymous Procedures
In NetLogo 6.0, tasks have been replaced by anonymous procedures. This means that task is
no longer a primitive, it's been replaced by the new arrow syntax for creating anonymous
procedures. Similarly, question mark variables like ?, ?1, and ?2 are now just ordinary names
in NetLogo and can be used to name procedure variables, let variables, or anonymous
procedure variables. Finally, is-reporter-task? and is-command-task? have been replaced by
is-anonymous-reporter? and is-anonymous-command?.
To make this transition easier, we've added an automatic conversion step which should allow
most models saved in NetLogo 5 to be converted to use the new syntax automatically. The
autoconverter has been a substantial piece of effort and we've tested it on all the models in
the models library. To use it, ensure the model compiles and run properly in NetLogo 5 or
later, then save it from NetLogo 5 or later. Then, simply open the model in NetLogo 6. If all
goes well, you'll see the converter has changed code like task [?1 + ?2] to [ [?1 ?2] -> ?1
+ ?2 ]. The question marks are meant to serve as temporary placeholders for conversion.
They enable your model to run, but you can (and should) replace these variables with
meaningful names. If you open a model with tasks and it has not been converted, the
autoconverter wasn't able to convert your model. Rather than attempt to autoconvert your
model and break something, the model will open, you will be shown the appropriate errors
and given a chance to edit your model.
While we have tested the autoconverter thoroughly, we expect there to be some cases it
doesn't cover.
If you make use of extensions that aren't yet compiled for NetLogo 6, the autoconverter
will not work until those extensions have been updated.
If your code uses run or runresult to evaluate strings containing tasks, the
autoconverter will not change those strings to be anonymous procedures. To make run
and runresult work as expected, look at strings in your model and change any which
rely on task or ?-variables to instead rely on anonymous procedures
If your model doesn't fall into the above categories and doesn't convert or converts incorrectly,
please email our feedback address and we'll be happy to offer whatever assistance we can.
Link reporters overhauled to be more consistent and flexible
In previous versions of NetLogo, link reporters have had a number of inconsistencies
regarding directed and undirected links. For example, my-links would report all links
connected to a turtle, whereas link-neighbors would only report neighbors connected by
undirected links. Furthermore, it was quite difficult to work with models where the links could
either be directed or undirected.
To alleviate these issues, the link primitives have been overhauled in 6.0. These changes
only affect existing models that use both directed and undirected links while also using the
unbreeded link primitives.
The changes are as follows:
Link reporters that contain the word "out" now utilize both directed, outgoing links and
undirected links. That is, they now specify links that can be used to get from the current
node to other nodes. For example, out-link-neighbor? will report true if the current
turtle is connected to the given turtle by either an outgoing directed link or an undirected
link. If you only want directed, outgoing links, you can use a breed-specific reporter or
my-out-links with [ is-directed? self ]. Generally, when working with models that
have both directed and undirected links, you will probably want to use the "out"
primitives for most things now.
Link reporters that contain the word "in" now utilize both directed, incoming links and
undirected links. That is, they now specify links that can be used to get to the current
node from other nodes. For example, in-link-neighbor? will report true if the current
turtle is connected to the given turtle by either an incoming directed link or an undirected
link. If you only want directed, incoming links, you can use a breed-specific reporter or
my-in-links with [ is-directed? self ].
Link reporters that do not specify "out" or "in" utilize all links.
Furthermore, there are no longer restrictions regarding which reporters can be used with
which breeds. For unbreeded links, this makes it possible to use the same primitives
regardless of whether your network ends up being directed or undirected.
The new behavior (including all changed primitives) is summarized by the following table,
where "un" refers to undirected links, "out" refers to directed, outgoing links, and "in" refers to
directed, incoming links.
New link reporter behavior
Old link reporter behavior
Removal of Applets
Oracle, the company behind Java, has announced that Java applets are deprecated (see this
blog post for more information). This comes as the major browsers have removed support for
plug-ins (like java applets) or announced that they plan to do so.
Instead of using applets to distribute your model, NetLogo offers the option to export to
NetLogo Web. While NetLogo Web doesn't yet offer the full functionality of desktop NetLogo
(in particular, extensions aren't supported), it is now capable of running most of the models in
the NetLogo models library and we hope that most model distributors will find that it meets
their needs. To export to NetLogo Web, choose the "Save As NetLogo Web" option from the
"File" menu.
Changes to the NetLogo User Interface
Users will notice several tweaks to the NetLogo User interface when opening NetLogo 6 for
the first time. We've removed the bar border above the view. To open the 3D View in 6.0, you
can right click on the view and choose "Switch to 3D View", or choose the same option from
the "Tools" menu. Ticks are now displayed in the interface tab toolbar beneath the speed
slider. To adjust the label used for "ticks" and other view properties, you can choose the
"Settings" button at the far right of the interface tab toolbar or right-click on the view and
choose "Edit..." from the context menu that appears.
Nobody Not Permitted as a Chooser Value
In NetLogo 6.0, nobody is no longer a valid chooser value. Just as you can't put turtle 0 or
turtles , nobody refers to a non-literal value which isn't supported in choosers. As part of this
transition, choosers containing nobody (or nobody within a nested list) will have all uses of
nobody changed to "nobody" when opened in NetLogo 6.0.
Breeds must have singular and plural names
In NetLogo 6.0, you must specify both plural and singular breed names. In prior versions,
declarations like breed [mice] were legal, but this support has been removed in 6.0. If you
have models which use only plural breed names, it is recommended that you convert them to
specify both names before opening in 6.0 since doing so will permit the NetLogo converter to
work most effectively on any other code in your model which needs conversion.
Removal of "Movie" Prims
The NetLogo movie prims hadn't been updated in quite some time and generated invalid
quicktime movie files. They have been replaced by prims in the new vid extension. The full
documentation for the vid extension is available in the Vid Extension section of the manual.
As with all extensions, users will need to include vid in the extensions section of their
NetLogo model.
Many of the movie primitives have direct parallels in the vid extension which can be found in
the following table:
movie prim
vid prim
movie-cancel
vid:reset-recorder
movie-close
vid:save-recording file-name
movie-grab-view
vid:record-view
movie-grab-interface vid:record-interface
movie-start file-name vid:start-recorder optional-width optional-height
movie-status
vid:recorder-status
When you first open a file in NetLogo 6.0, your file will be automatically converted to use the
new primitives. This will include adding a new global variable - _recording-save-file-name to
track the name of the active recording, as well as adding the vid extension to the model. You
should verify that the conversion took place correctly. There is no replacement for movie-setframe-rate. The vid extension records frames at 25 per second, slightly more than the default
15 frames-per-second of the movie prims. If your recording is sensitive to framerate, consider
recording each existing frame twice (2/25 is fairly close to 1/15) or consider using a
postprocessing tool (like gstreamer or ffmpeg) to adjust the video playback speed.
Improved Name Collision Detection
In NetLogo 6.0, expanded error-checking in the NetLogo compiler causes models which
define undirected-link-breed [ undirected-links undirected-link ] and/or directedlink-breed [ directed-links directed-link ] to error for redefining a primitive reporter
(either is-directed-link? or is-undirected-link?). If your model doesn't use is-directedlink? or is-undirected-link? at all, simply changing the breed names should resolve the
error.
If you used either of the is--link? prim, there are several ways you might
modify your model to account for this change. If your model has no other breeded links,
consider removing the link breed and using the built-in link primitives. If your model has other
breeded links, but only of different directedness, simply changing the breed name (and all
related primitive names) should resolve the problem. Note that in this case is-directed-link?
and/or is-undirected-link? continue to behave the same as before. If your model has other
breeded links of the same directedness, the change will vary depending on your model. The
breed name(s) must be changed, but you must decide whether you used is-directed-link? /
is-undirected-link? to check link directedneess or to check that link breed membership. If
you used it to check link directedness leaving it as-is should keep the current behavior of the
model. Otherwise, it can simply be replaced by is-?.
Removal of hubnet-set-client-interface
The hubnet-set-client-interface primitive was rendered obsolete by the introduction of the
HubNet client editor and end of support for calculator HubNet. We have found it used in very
few models and have decided to remove it from the language. On opening an existing model
in 6.0, the autoconverter should remove all uses of hubnet-set-client-interface from your
code.
Improved & Updated Extensions API
One of our goals in NetLogo 6.0 has been to make it easier to develop extensions and easy
to develop more powerful extensions. To that end, we've bumped the extension API from 5.0
to 6.0. Existing extensions will need to recompile changing the "NetLogo-Extension-APIVersion" in their jar's MANIFEST.MF from 5.0 to 6.0.
Some of the changes we've made to the extensions API include:
now allows access to the current world and workspace objects
without requiring a cast to an org.nlogo.nvm.ExtensionContext.
org.nlogo.api.Workspace has been introduced as a stable API for extensions to depend
on.
A NetLogo jar is now available from BinTray.
org.nlogo.api.Context
For a full list of changes between 5.0 and 6.0, please visit our Extension Transition Guide on
GitHub.
In service of making it easier to build extensions, we've expanded and improved the NetLogo
Extension Plugin for sbt, the Scala Build Tool. Sbt is a powerful tool for building JVM projects
and can be used in projects that use Scala, Java, or a combination of the two. We're now
using the Extension Plugin to build all of the bundled extensions and we strongly recommend
extension authors take advantage of the plugin as it makes configuring a NetLogo extension
build extremely straightforward. The plugin handles fetching the NetLogo jar which extensions
compile against as well as generation of a jar for the extension containing the appropriate
metadata.
Add range primitive
A new range primitive was added in NetLogo 6. As "range" may appear in existing models as
a procedure or variable name, we have added an autoconversion step which will ensure that
these models continue to operate immediately upon opening in NetLogo 6. Existing uses of
range in models authored before NetLogo 6 will be converted to _range upon first opening in
NetLogo 6. Once the model opens, you can rename _range to suit your model.
Changes for NetLogo 5.2
hsb primitives
In 5.2, the hsb primitives have been changed to work with the standard scale values of 360
for hue, and 100 for saturation and brightness. This affects the primitives hsb, extract-hsb and
approximate-hsb.
The old primitives, scaled to 255, are automatically transitioned to and have been renamed
__hsb-old, __extract-hsb-old and __approximate-hsb-old.
GoGo extension
The GoGo extension has been upgraded to use newer GoGo boards with the HID interface.
Many of the older primitives no longer work, and will alert you to upgrading your GoGo
board's firmware.
If you need to continue to use a serial interface, you can use the bundled gogo-serial
extension. Change your model to use gogo-serial as opposed to gogo. More details [here]
(https://github.com/NetLogo/NetLogo/wiki/GoGo-Upgrade).
If you cannot upgrade to use the new HID extension nor the new serial extension, the original
extension can be found at https://github.com/NetLogo/GoGo-RXTX-Extension
Changes for NetLogo 5.0
Plotting
In 5.0, you don't have to put your plotting code in the Code tab anymore. Instead, you can put
it inside the plots themselves, in the Interface tab.
Nonetheless, the old style and all of the existing plotting primitives are still supported. We
recommend changing your model to use the new style, but if you don't, it should still work.
The following example shows how to change a model to use the new style. Suppose you
have a typical NetLogo 4.1 model with one plot called "populations" and two pens called
"robots" and "humans". The old code might look like:
to setup
clear-all
...
do-plotting
end
to go
...
tick
do-plotting
end
to do-plotting
set-current-plot "populations"
set-current-plot-pen "robots"
plot count robots
set-current-plot-pen "humans"
plot count humans
end
Here are the steps to make the transition:
Copy the plot count robots command and paste it into the Update Commands field for
the robots pen in the plot edit dialog. Remove it from the do-plotting procedure.
The plot count humans command can be moved in the same way for the humans pen.
After those lines are removed from the do-plotting procedure, it doesn't actually do
anything anymore! Remove it.
The final step is to replace the do-plotting procedure calls in setup and go. In setup, the
do-plotting call should be changed to reset-ticks. In go , the do-plotting call should be
changed to tick. reset-ticks and tick will both cause plotting to happen automatically.
The resulting (much simpler) code looks like this:
to setup
clear-all
...
reset-ticks
end
to go
...
tick
end
For more details on how plotting works in NetLogo 5.0, see the Plotting Sections of the
Programming Guide and the Interface Guide. For details on how plotting interacts with the tick
counter, read on.
Tick counter
The way the tick counter works has changed in 5.0. Instead of being initially set to 0, the tick
counter is initially blank.
reset-ticks
You must use reset-ticks to start the tick counter at 0 before using ticks, tick or tick-
advance
for the first time.
should go at the end of your setup procedure. Putting it there will allow your
model to work with 5.0's new plotting features.
reset-ticks
reset-ticks
and plotting
In 5.0, you don't have to put your plotting code in the Code tab anymore. Instead, you can put
it inside the plots themselves, in the Interface tab. Code inside plots is triggered by resetticks and tick. Resetting the tick counter runs plot setup code, and then it also runs plot
update code to plot the initial state of the model. The initial state of the model won't be in
place until the end of setup, so that's why reset-ticks should go at the end.
__clear-all-and-reset-ticks
In order for models from previous NetLogo versions to work in 5.0 without changes, when an
old model is opened in 5.0, any occurrences of clear-all (or ca) are automatically changed to
__clear-all-and-reset-ticks, which combines the effects of clear-all and reset-ticks. The
two underscores on the name indicate that this is not a normal primitive, but exists only for
backwards compatibility.
You should remove __clear-all-and-reset-ticks from your code, replace it with clear-all,
and put reset-ticks at the end of your setup procedure. (This doesn't happen automatically
because the structure of NetLogo models is too free-form for an automatic converter to
reliably make the change for you.)
Unicode characters
NetLogo 5.0 fully supports international characters cross-platform, using the Unicode
character set. NetLogo 5.0 model files always represent Unicode characters using the UTF-8
encoding.
Previous versions of NetLogo allowed Unicode characters to be used in some contexts.
However, model files were saved in the platform's default encoding, which on most systems
was something other than UTF-8. Characters were handled correctly on the same platform
(e.g. two Windows machines), but could be altered if the model was moved between platforms
(e.g. from Windows to Mac or vice versa).
When opening an existing model in NetLogo 5.0, if the model contains international or other
non-ASCII characters, the characters may be interpreted incorrectly, because they were
originally written in a platform-specific encoding, but then read back in in UTF-8.
If only a few characters are affected, you might find it easiest just to fix them manually.
But if you expect a large number of characters to be affected, and you want them translated
automatically, you can use a third party utility to re-encode your .nlogo file from its original
encoding into UTF-8. After conversion, open the model in NetLogo 5.0 and all characters
should be correct.
Info tabs
NetLogo 5.0 uses the Markdown markup language to allow you to format your Info tab,
including headers, bold and italics, images, and so forth.
Earlier versions of NetLogo used a custom markup language with much more limited
capabilities.
When opening a model from an older version, NetLogo 5.0 translates your old markup into
Markdown. Most of the time this produces good results, but you may want to check the
results yourself and make sure that your Info tab still looks good.
Model speed
In NetLogo 5.0 every model has a "target frame rate" which affects the default speed at which
the model runs, when the speed slider is in the middle, on the "normal speed" setting.
The default target frame rate for new models, and for models that were created in earlier
versions of NetLogo, is 30 frames per second. If you are using tick-based updates, as we
recommend for most models, then that translates to 30 ticks per second.
If your model runs slower in 5.0 than it ran in 4.1, it's probably just because its speed is being
limited by this rate. If you want, you can press the Settings button in the Interface tab and
change the frame rate to a higher number.
Some old models used the every command to set a default speed. In most case this can be
now removed from the code, and the target frame rate setting used instead.
List performance
The underlying data structure for NetLogo lists has changed.
In NetLogo 4.1, a NetLogo list was represented internally as a singly linked list. Some
operations on singly linked lists are fast (such as first and butfirst) but others are slow
because they could require traversing the whole list (such as item and last).
In NetLogo 5.0, lists are now actually trees internally. As a result, some operations are a little
slower, but other operations are drastically faster on long lists. See the Lists section of the
Programming Guide for details.
Some models may run a little slower with the new data structure, especially if you make
heavy use of short lists. But other models will run faster -- perhaps dramatically faster.
Some special ways of writing list-processing code that were useful in NetLogo 4.1 are no
longer needed in 5.0. For example, since in 4.1 fput was fast and lput was slow, modelers
sometimes built up lists in reverse order using fput, perhaps calling reverse later to restore
the intended order. In NetLogo 5.0, you don't need to code that way anymore. fput and lput
are the same speed.
Extensions API
If you are the author of an extension, you will need to recompile it against the 5.0 NetLogo.jar
and lib directory for it to work with 5.0.
You may also need to be aware of the following changes:
Syntax constants
The code for specifying the syntax of a primitive has changed slightly, for example
is now Syntax.StringType(). (From Java, the pair of parentheses at the
end is required. In Scala, you can omit them.)
Syntax.TYPE_STRING
LogoList construction
One significant change is that org.nlogo.api.LogoList no longer has a public constructor.
Instead, there are two new ways to construct a LogoList.
If you have a java.lang.Iterable, you can copy the contents into a fresh LogoList by passing
it to the static method LogoList.fromJava(). See the array extension source code for a
sample usage.
Or, to build up a new list one item a time, use org.nlogo.api.LogoListBuilder. The
Extensions Guide has sample code showing the use of LogoListBuilder.
Primitive classes
In prior NetLogo versions, the extensions API required that each extension primitive have its
own separate top-level class with a no-argument constructor. These limitations have now
been lifted. Also, api.Primitive objects are now made only once, when the extension is
loaded, instead of every time the Code tab was recompiled.
Changes for NetLogo 4.1
Combining set and
of
The following syntax is no longer supported:
set [] of
Commands of this form must be rewritten using ask:
ask [ set ]
Or, if the new value must be computed by the asking agent and not by the agent whose
variable is being set:
;; OPTION #1 (using let):
let new-value
ask [ set new-value ]
;; OPTION #2 (using myself):
ask [ set [value] of myself ]
So for example, this:
set [color] of turtle 0 red
Can be rewritten as:
ask turtle 0 [ set color red ]
It is not necessary to use let or myself since red is red from the point of view of both agents.
However, this:
set [color] of turtle 0 color
Must be rewritten as:
let new-color color
ask turtle 0 [ set color new-color ]
or
ask turtle 0 [ set color [color] of myself ]
in order not to change the meaning, since the two agents may have different starting values
for color. The form using myself is briefer, but the former using let may be considered
clearer, depending on context and individual preference.
Changes for NetLogo 4.0
Who numbering
Prior to NetLogo 4.0, a dead turtle's who number (stored in the who turtle variable) could be
reassigned to a later newborn turtle. In NetLogo 4.0, who numbers are never reused until who
numbering is reset to 0 by the clear-all or clear-turtles command. This change in behavior
may break a few old models.
Turtle creation: randomized vs. "ordered"
NetLogo 4.0 provides two different observer commands for creating turtles, create-turtles
(crt) and create-ordered-turtles (cro).
gives the new turtles random colors and random integer headings. cro assigns colors
sequentially and gives the turtles sequential equally spaced headings, with the first turtle
facing north (heading of 0).
crt
Prior to NetLogo 4.0, the crt command behaved the way cro does now. If your old model
depends on the "ordered" behavior, you will need to change your code to use cro instead of
crt.
It is common for old models that used crt to contain extra commands to randomize the new
turtles' headings, for example rt random 360 or set heading random 360 . These commands
are no longer necessary when used inside crt.
Adding strings and lists
Prior to NetLogo 4.0, the + (addition) operator could be used to concatenate strings and join
lists. In current NetLogo, + only works on numbers. To concatenate strings, use the word
primitive; to join lists together, use the sentence primitive. This language change was made to
increase the speed of code that uses +.
Old code:
print "There are " + count turtles + " turtles."
New code:
print (word "There are " count turtles " turtles.")
Likewise, if you need to concatenate lists, use SENTENCE.
This change is not handled automatically when converting old models; users will need to
change their code by hand.
We know this change will be awkward for users who are used to the old syntax. We have
made this change for efficiency and consistency. We can implement an addition operator that
only adds numbers much more efficiently than one that handles several different data types.
Because addition is such a common operation, NetLogo's overall speed is affected.
The -at primitives
The observer may no longer use patch-at , turtles-at, and BREEDS-at . Use patch, turtles-on
patch, and BREEDS-on patch instead. Note that patch now rounds its inputs (before it only
accepted integer inputs).
Links
NetLogo 3.1 had supports for using links to connect turtles to make networks, graphs, and
geometric figures. The links were themselves turtles.
In NetLogo 4.0, instead of links being turtles, links are now an independent fourth agent type,
right alongside observer, turtles, patches. The primitives involving links are no longer
considered experimental; they are now fully part of the language.
Models that use the old, experimental turtle-based link primitives will need to be updated to
use link agents. The differences are not huge, but hand updating is required.
Links are documented in the Links section of the Programming Guide, and in the NetLogo
Dictionary entries for the link primitives. See the Networks section of the Models Library for
example models that use links. There are also some link-based Code Examples.
First you will need to remove any breeds called "links" if you are only using one type of links
then you will not have to use breeds at all. If you are using multiple types of links see
undirected-link-breed and directed-link-breed. Commands and reporters that contain the
word "links" (like __create-links-with, etc.) will automatically be converted to the new form
without underscores (create-links-with ). However, primitives that use a different breed
name (such as "edges") will not be converted. You will need to remove the underscores by
hand and unless you are declaring a link breed with that name you will need to change the
breed designation to "links".
The commands remove-link(s)-with/from/to no longer exist. Instead you should ask the
links in question to die.
For example:
ask turtle 0 [ __remove-links-with link-neighbors ]
becomes
ask turtle 0 [ ask my-links [ die ] ]
Several of the layout commands have slightly different inputs, the first two inputs are
generally a turtle agentset and a link agentset to perform the layout on. See the dictionary
entries for details. layout-spring , layout-radial layout-tutte
You may also need to rearrange the declaration of turtles-own variables, since links were
once actually turtles. Any variables that apply to links should be moved into a links-own block.
Since links are no longer turtles they no longer have the built-in turtle variables (though some
of the link variables are the same such as color and label. If you formerly used the location of
link turtles you will now need to calculate the midpoint of the link. This is fairly simple in a nonwrapping world.
to-report link-xcor
report mean [xcor] of both-ends
end
to-report link-ycor
report mean [ycor] of both-ends
end
it is a little bit trickier in a wrapping world but still fairly straightforward.
to-report link-xcor
let other-guy end2
let x 0
ask end1
[
hatch 1
[
face other-guy
fd [distance other-guy] of myself / 2
set x xcor
die
]
]
report x
end
and similarly for ycor.
If you used either the size or heading of the link turtles you can use the reporters link-length
and link-heading instead.
New "of" syntax
We have replaced three different language constructs, -of (with hyphen), value-from, and
values-from with a single of construct (no hyphen).
old
color-of turtle 0
new
[color] of turtle 0
value-from turtle 0 [size * size] [size * size] of turtle 0
mean values-from turtles [size]
mean [size] of turtles
When of is used with a single agent, it reports a single value. When used with an agentset, it
reports a list of values (in random order, since agentsets are always in random order).
Note that when opening old models in the new version, -of , value-from, and values-from will
automatically be converted to use "of" instead, but some nested uses of these constructs are
too complex for the converter and must be converted by hand.
Serial ask
The ask command is now serial rather than concurrent. In other words, the asked agents will
run one at a time. Not until one agent completely finishes the entire body of the ask does the
next agent start.
Note that even the old ask was never truly concurrent; we simulated concurrent execution by
interleaving execution among the agents using a turn-taking mechanism described in the
NetLogo FAQ.
We have made this change because in our experience, users often wrote models that
behaved in unexpected ways due to the simulated concurrency, but rarely wrote models that
benefited from the simulated concurrency. Models exhibiting unexpected behavior could
usually be fixed by adding the without-interruption command in the right places, but it was
difficult for users to know whether that command was needed and if so, where.
In NetLogo 4.0, without-interruption is no longer necessary unless your model uses askconcurrent (or a turtle or patch forever button containing code that depends on simulated
concurrency). In most models, all uses of without-interruption can be removed.
The simulated concurrency formerly employed by "ask" is still accessible in three ways:
You may use the ask-concurrent primitive instead of ask to get the old simulated
concurrency. (We don't recommend this, though.)
Commands issued in the Command Center directly to turtles, patches, or links have an
implied ask-concurrent.
Turtle, patch, and link forever buttons have an implied ask-concurrent as well.
Note that ask itself is always serial regardless of the context in which it is used, however.
In our own Models Library, models that make use of this concurrency are rare. A prominent
example, though, is Termites, which uses a concurrent turtle forever button.
Tick counter
NetLogo now has a built-in tick counter for representing the passage of simulated time.
You advance the counter by one using the tick command. If you need to read its value,
there's a reporter called ticks. The clear-all command resets the tick counter; so does
reset-ticks.
In most models the tick counter will be integer-valued, but if you want to use smaller
increments of time, you can use the tick-advance command to advance the tick counter by
any positive amount, including fractional amounts. Some Models Library models that use
tick-advance are Vector Fields and the GasLab models.
The value of the tick counter is displayed in the toolbar at the top of the Interface tab. (You
can use the Settings... button in the toolbar to hide the tick counter, or change the word "ticks"
to something else.)
View update modes
In the past, NetLogo always tried to update the view about 20 times a second. We're now
calling that "continuous" view updates. The biggest problem with it was that you usually want
updates to happen between model ticks, not in the middle of a tick, so we had a checkbox on
buttons that (by default) forced a display update after every button iteration. That made sure
updates happened between ticks, but it didn't get rid of the intermediate updates. You had to
use no-display and display to lock them out.
We still support continuous updates. They are the default when you start up NetLogo. But
most Models Library models now use tick-based updates. With tick-based updates, updates
happen only when the tick counter advances. (The display command can be used to force
additional updates; see below.)
The advantages of tick-based updates as we see them are as follows:
1. Consistent, predictable view update behavior which does not vary from computer to
computer or from run to run.
2. Intermediate updates can confuse the user of your model by letting them see things
they aren't supposed to see, which may be misleading.
3. Increased speed. Updating the view takes time, so if one update per tick is enough, then
enforcing than there is only one update per tick will make your model faster.
4. Instead of having a "force view update" checkbox in every button like in NetLogo 3.1, we
only need one choice which applies to the entire model.
5. Using the speed slider to slow down a model now just inserts pauses between ticks. So
with tick-based updates, setup buttons are no longer affected by the speed slider. This
was a real annoyance with the old speed slider. (The annoyance persists for models
that use continuous updates, though.)
As mentioned above, most models in our Models Library now use tick-based updates.
Even for models that would normally be set to tick-based updates, it may be useful to switch
to continuous updates temporarily for debugging purposes. Seeing what's going on within a
tick, instead of only seeing the end result of a tick, could help with troubleshooting.
If you switch your model to use tick-based updates, you'll also need to add the tick command
to your code, otherwise the view won't update. (Note that the view still always updates when a
button pops up or a command entered in the command center finishes, though. So it's not like
the view will just stay frozen indefinitely.)
How to make a model use ticks and tick-based updates
Here are the steps to follow to convert your model to use ticks and tick-based updates in
NetLogo 4.0:
1. In the Interface tab toolbar, on the right hand side where it says "update view:", change
the setting from "continuously" to "on ticks".
2. Add the tick command to your go procedure, at or near the end. In Models Library
models we always put tick after the agents move but before any plotting commands.
That's because the plotting commands might contain something like plotxy ticks ...
and we want the new value of the tick counter used, not the old one. Most models don't
refer to the tick counter in their plotting commands, but nonetheless, for consistency and
to avoid mistakes we suggest always putting tick before the plotting commands.
Some models will require some additional changes:
1. If your model already has a global "ticks" or "clock" or "time" variable, get rid of it. Use
the tick command and ticks reporter instead. (If your model uses fractional increments
of time, use tick-advance instead of tick.) If you had a monitor for that variable, you can
get rid of it; there's now a tick counter in the toolbar.
2. clear-all resets the tick counter to zero. If you don't use clear-all in your setup
procedure, then you may need to add reset-ticks to reset the counter to zero.
3. If you used no-display and display to prevent view updates from happening in the
middle of go, you can get rid of them.
4. If your model needs to update the view without advancing the tick counter (examples:
Party, Dice Stalagmite, network models with animated layout, models with mouse
interaction buttons), use the display command to force additional view updates so the
user can see what is going on.
Speed slider
Previous versions of NetLogo had a speed slider that could be used to make models run
slower, so you can see what's going on.
In NetLogo 4.0, the slider can be used to speed up models as well. It does this by updating
the view less frequently. Updating the view takes time, so the fewer updates, the faster the
model runs.
The default position of the slider is in the center. When you're at the center, the slider says
"normal speed".
As you move the slider away from the center position, the model will gradually run faster or
slower.
At very high speeds, view updates become very infrequent and may be separated by several
seconds. It may feel like the model is actually running slower, since the updates are so
infrequent. But watch the tick counter, or other indicators such as plots, and you'll see that
yes, the model really is running faster. If the infrequent updates are disconcerting, don't push
the slider so far over.
When using tick-based updates, slowing the model down does not cause additional view
updates. Rather, NetLogo simply pauses after each tick.
When using continuous updates, slowing the model down means view updates become more
closely spaced. If you push the speed slider more than halfway to the left, the model will be
running so slowly that you can watch turtles moving one at a time! This is new in NetLogo 4.0;
in previous NetLogo versions, no matter how slowly you ran a model, you would never see the
agents in an ask moving one at a time; all the agents in an ask always appeared to move
together.
Numbers
NetLogo no longer maintains an internal distinction between integers and floating point
numbers. So for example:
Old:
observer>
3
observer>
3.0
observer>
3
observer>
3.0
observer>
true
print 3
print 3.0
print 1 + 2
print 1.5 + 1.5
print 3 = 3.0
(The last line shows that although the distinction between integer 3 and floating point 3.0 was
maintained, the two numbers were still considered equal.)
New:
observer>
3
observer>
3
observer>
3
observer>
3
observer>
true
print 3
print 3.0
print 1 + 2
print 1.5 + 1.5
print 3 = 3.0
We expect that only rare models will be negatively impacted by this change.
A benefit of this change is that NetLogo now supports a much larger range of integers. The
old range was -2,147,483,648 to 2,147,483,647 (around +/- 2 billion); the new range is +/9,007,199,254,740,992 (around +/- 9 quadrillion).
Agentset building
NetLogo 3.1 (and some earlier versions) included primitives called turtles-from and patchesfrom that were occasionally useful for building agentsets. In NetLogo 4.0, these primitives
have been replaced with new primitives called turtle-set and patch-set that are much more
flexible and powerful. (link-set exists as well.) See the entries for these primitives in the
NetLogo Dictionary. Models that use the old turtles-from and patches-from will need to be
altered by hand to use the new primitives.
RGB Colors
In NetLogo 3.1 RGB and HSB colors could be approximated as NetLogo colors using the rgb
and hsb primitives. These have been renamed to approximate-rgb and approximate-hsb and
now expect inputs in the range 0-255, not 0-1.
The full RGB spectrum is now available in NetLogo so it may no longer be necessary to use
these primitives at all. You can set any color variable to a three-item RGB list, with values in
the 0-255 range, and get that exact color. See the Color section of the Programming Guide
for details.
Tie
In previous versions __tie was provided as an experimental feature. As of NetLogo 4.0 links
have a tie-mode variable which can be set to "none", "free", or "fixed" . In 4.0 tie is now a
link-only primitive. This means that to tie turtle 1 to turtle 0 you write:
ask turtle 0 [ create-link-to turtle 1 [ tie ] ]
See the Tie section of the programming guide for details.
Changes for NetLogo 3.1
Agentsets
If your model is behaving strangely or incorrectly, it may be because since NetLogo 3.1,
agentsets are now always in random order. In prior versions of NetLogo, agentsets were
always in a fixed order. If your code depended on that fixed order, then it won't work anymore.
How to fix your model to work with randomized agentsets depends on the details of what your
code is doing. In some situations, it is helpful to use the sort or sort-by primitives to convert
an agentset (random order) into a list of agents (fixed order). See "Lists of agents" in the Lists
section of the Programming Guide.
Wrapping
If you are seeing pieces of turtle shapes wrapping around the view edges, it's because
NetLogo 3.0 allowed you to turn off such wrapping in the view without affecting the behavior
of the model. Since NetLogo 3.1, if you don't want the view to wrap you must make it so the
world doesn't wrap, using the new topology feature. Making this change may require other
changes to your model, though. See the Topology section of the Programming Guide for a
thorough discussion of how to convert your model to take advantage of this new feature.
Random turtle coordinates
Many models made in NetLogo 3.0 or earlier use setxy random world-width random worldheight to scatter turtles randomly, using either random or random-float . It only works if world
wrapping is on.
(Why? Because when wrapping is on, you can set coordinates of turtles to numbers beyond
the edge of the world and NetLogo will wrap the turtle to the other side. But in worlds that
don't wrap setting the x or y coordinates of a turtle to a point outside the bounds of the world
causes a runtime error. The world wrap settings were added in NetLogo 3.1. See the
Topology section of the Programming Guide for more information.)
To fix your model so that it works regardless of the wrapping settings, use one of these two
commands instead:
setxy random-xcor random-ycor
setxy random-pxcor random-pycor
The two commands are a bit different. The first command puts the turtle on a random point in
the world. The second command puts the turtle on the center of a random patch. An even
more concise way to put a turtle on the center of a random patch is:
move-to one-of patches
Shapes Editor Guide
The Turtle and Link Shape Editors allows you to create and save turtle and link designs.
NetLogo uses fully scalable and rotatable vector shapes, which means you can create
designs by combining basic geometric elements, which can appear on-screen in any size or
orientation.
Getting started
To begin making shapes, choose Turtle Shapes Editor or Link Shapes Editor in the Tools
menu. A new window will open listing all the shapes currently in the model, beginning with
default, the default shape. The Shapes Editor allows you to edit shapes, create new shapes,
and borrow from another model. You can also import turtle shapes from a library of preexisting shapes.
Importing shapes
Every new model in NetLogo starts off containing a small core set of frequently used shapes.
Many more turtle shapes are available by using the Import from library... button. This brings
up a dialog where you can select one or more shapes and bring them into your model. Select
the shapes, then press the Import button.
Similarly, you can use the Import from model... button to borrow shapes from another model.
Default shapes
Here are the turtle shapes that are included by default in every new NetLogo model:
First row: default, airplane, arrow, box, bug, butterfly, car
Second row: circle, circle 2, cow, cylinder, dot, face happy, face neutral
Third row: face sad, fish, flag, flower, house, leaf, line
Fourth row: line half, pentagon, person, plant, sheep, square, square 2
Fifth row: star, target, tree, triangle, triangle 2, truck, turtle
Sixth row: wheel, x
Shapes library
And here are the shapes in the shapes library (including all of the default shapes, too):
By default there is only one Link shape in a model, that is "default". This shape is simply a
single straight line with a simple arrowhead (if the link happens to be directed).
Creating and editing turtle shapes
Pressing the New button will make a new shape. Or, you may select an existing shape and
press Edit.
Tools
In the upper left corner of the editing window is a group of drawing tools. The arrow is the
selection tool, which selects an already drawn element.
To draw a new element, use one of the other seven tools:
The line tool draws line segments.
The circle, square, and polygon tools come in two versions, solid and outline.
When using the polygon tool, click the mouse to add a new segment to the polygon. When
you're done adding segments, double click.
After you draw a new element, it is selected, so you can move, delete, or reshape it if you
want:
To move it, drag it with the mouse
To delete it, press the Delete button.
To reshape it, drag the small "handles" that appear on the element only when it is
selected.
To change its color, click on the new color.
Previews
As you draw your shape, you will also see it in five smaller sizes in the five preview areas
found near the bottom of the editing window. The previews show your shape as it might
appear in your model, including how it looks as it rotates. The number below each preview is
the size of the preview in pixels. When you edit the view, patch size is also measured in
pixels. So for example, the preview with "20" below it shows you how your shape would look
on a turtle (of size 1) on patches of size 20 pixels.
The rotatable feature can be turned off if you want a shape that always faces the same way,
regardless of the turtle's heading.
Overlapping shapes
New elements go on top of previous elements. You can change the layering order by
selecting an element and then using the Bring to front and Send to back buttons.
Undo
At any point you can use the Undo button to undo the edit you just performed.
Colors
Elements whose color matches the Color that changes (selected from a drop-down menu -the default is gray) will change color according to the value of each turtle's color variable in
your model. Elements of other colors don't change. For example, you could create cars that
always have yellow headlights and black wheels, but different body colors.
Other buttons
The "Rotate Left" and "Rotate Right" buttons rotate elements by 90 degrees. The "Flip
Horizontal" and "Flip Vertical" buttons reflect elements across the axes.
These four buttons will rotate or flip the entire shape, unless an element is selected, in which
case only that element is affected.
These buttons are especially handy in conjunction with the "Duplicate" button if you want to
make shapes that are symmetrical. For example, if you were making a butterfly, you could
draw the butterfly's left wing with the polygon tool, then duplicate the wing with the "Duplicate"
button, then turn the copy into a right wing with the "Flip Horizontal" button.
Shape design
It's tempting to draw complicated, interesting shapes, but remember that in most models, the
patch size is so small that you won't be able to see very much detail. Simple, bold, iconic
shapes are usually best.
Keeping a shape
When the shape is done, give it a name and press the Done button at the bottom of the
editing window. The shape and its name will now be included in the list of shapes along with
the "default" shape.
Creating and editing link shapes
Managing link shapes is very similar to managing turtle shapes. So, you can create a new
shape by pressing the New button or you can edit existing shapes. When you are done
editing a shape press Done if you want to keep it.
Changing link shape properties
There are several different properties for each link shape that you are allowed to change:
Name - link shapes can have the same name as turtle shapes but must be unique
among link shapes.
Direction Indicator - the direction indicator (the little arrow on directed links) is just like
the turtle vector shapes, you can edit it using the same editor by pressing the Edit
button.
Curviness - this is the amount of bend in a link expressed in patches (this is particularly
useful if you have directed links going in both directions so you can discern both links)
Number of lines: You can have 1, 2, or 3 lines in each link shape, you control this by
selecting line patterns in the "left line", "middle line", and "right line" selection boxes.
Dash pattern of lines: There are several dashed line patterns available in the selection
boxes so not all lines need be solid.
Here are some link shapes with various properties:
Using shapes in a model
In the model's code or in the command center, you can use any of the shapes that are in the
model (though only turtles can have turtle shapes and only links can have link shapes). For
example, suppose you want to create 50 turtles with the shape "rabbit". Provided there is
some turtle shape called rabbit in this model, give this command to the observer in the
command center:
observer> crt 50
And then give these commands to the turtles to spread them out, then change their shape:
turtles> fd random 15
turtles> set shape "rabbit"
Voila! Rabbits! Note the use of double quotes around the shape name. Shape names are
strings.
Similarly, you can set the shape variable of links. Assuming there is a link shape called "road"
in this model:
observer> crt 5 [ create-links-with other turtles ]
turtles> fd 5
links> set shape "road"
The set-default-shape command is also useful for assigning shapes to turtles and links.
BehaviorSpace Guide
This guide has three parts:
What is BehaviorSpace?: A general description of the tool, including the ideas and
principles behind it.
How It Works: Walks you through how to use the tool and highlights its most commonly
used features.
Advanced Usage: How to use BehaviorSpace from the command line, or from your
own Java code.
What is BehaviorSpace?
BehaviorSpace is a software tool integrated with NetLogo that allows you to perform
experiments with models.
BehaviorSpace runs a model many times, systematically varying the model's settings and
recording the results of each model run. This process is sometimes called "parameter
sweeping". It lets you explore the model's "space" of possible behaviors and determine which
combinations of settings cause the behaviors of interest.
If your computer has multiple processor cores, then by default, model runs will happen in
parallel, one per core.
Why BehaviorSpace?
The need for this type of experiment is revealed by the following observations. Models often
have many settings, each of which can take a range of values. Together they form what in
mathematics is called a parameter space for the model, whose dimensions are the number of
settings, and in which every point is a particular combination of values. Running a model with
different settings (and sometimes even the same ones) can lead to drastically different
behavior in the system being modeled. So, how are you to know which particular
configuration of values, or types of configurations, will yield the kind of behavior you are
interested in? This amounts to the question of where in its huge, multi-dimension parameter
space does your model perform best?
For example, suppose you want speedy synchronization from the agents in the Fireflies
model. The model has four sliders -- number, cycle-length, flash-length and number-flashes -that have approximately 2000, 100, 10 and 3 possible values, respectively. That means there
are 2000 * 100 * 10 * 3 = 600,000 possible combinations of slider values! Trying combinations
one at a time is hardly an efficient way to learn which one will evoke the speediest
synchronization.
BehaviorSpace offers you a much better way to solve this problem. If you specify a subset of
values from the ranges of each slider, it will run the model with each possible combination of
those values and, during each model run, record the results. In doing so, it samples the
model's parameter space -- not exhaustively, but enough so that you will be able to see
relationships form between different sliders and the behavior of the system. After all the runs
are over, a dataset is generated which you can open in a different tool, such as a
spreadsheet, database, or scientific visualization application, and explore.
By enabling you to explore the entire "space" of behaviors a model can exhibit,
BehaviorSpace can be a powerful assistant to the modeler.
How It Works
To begin using BehaviorSpace, open your model, then choose the BehaviorSpace item on
NetLogo's Tools menu.
Managing experiment setups
The dialog that opens lets you create, edit, duplicate, delete, and run experiment setups.
Experiments are listed by name and how by model runs the experiment will consist of.
Experiment setups are considered part of a NetLogo model and are saved as part of the
model.
To create a new experiment setup, press the "New" button.
Creating an experiment setup
In the new dialog that appears, you can specify the following information. Note that you don't
always need to specify everything; some parts can be left blank, or left with their default
values, depending on your needs.
Experiment name: If you have multiple experiments, giving them different names will help
you keep them straight.
Vary variables as follows: This is where you specify which settings you want varied, and
what values you want them to take. Variables can include sliders, switches, choosers, and
any global variables in your model.
Variables can also include max-pxcor, min-pxcor, max-pycor and min-pycor, world-width,
world-height and random-seed. These are not, strictly speaking, variables, but BehaviorSpace
lets you vary them as if they were. Varying the world dimensions lets you explore the effect of
world size upon your model. Since setting world-width and world-height does not necessarily
define the bounds of the world how they are varied depends on the location of the origin. If
the origin is centered, BehaviorSpace will keep it centered so the values world-width or
world-height must be odd. If one of the bounds is at zero that bound will be kept at zero and
the other bound will move, for example if you start with a world with min-pxcor = 0 max-pxcor
= 10 and you vary world-width like this:
["world-width" [11 1 14]]
will stay at zero and max-pxcor will set to 11, 12, and 13 for each of the runs. If
neither of these conditions are true, the origin is not centered, nor at the edge of the world
you cannot vary world-height or world-width directly but you should vary max-pxcor, maxpycor, min-pxcor and min-pycor instead.
min-pxcor
Varying random-seed lets you repeat runs by using a known seed for the NetLogo random
number generator. Note that you're also free to use the random-seed command in your
experiment's setup commands. For more information on random seeds, see the Random
Numbers section of the Programmer's Guide.
You may specify values either by listing the values you want used, or by specifying that you
want to try every value within a given range. For example, to give a slider named number
every value from 100 to 1000 in increments of 50, you would enter:
["number" [100 50 1000]]
Or, to give it only the values of 100, 200, 400, and 800, you would enter:
["number" 100 200 400 800]
Be careful with the brackets here. Note that there are fewer square brackets in the second
example. Including or not including this extra set of brackets is how you tell BehaviorSpace
whether you are listing individual values, or specifying a range.
Also note that the double quotes around the variable names are required.
You can vary as many settings as you want, including just one, or none at all. Any settings
that you do not vary will retain their current values. Not varying any settings is useful if you
just want to do many runs with the current settings.
What order you list the variables in determines what order the runs will be done in. All values
for a later variable will be tried before moving to the next value for an earlier variable. So for
example if you vary both x and y from 1 to 3, and x is listed first, then the order of model runs
will be: x=1 y=1, x=1 y=2, x=1 y=3, x=2 y=1, and so on.
Repetitions: Sometimes the behavior of a model can vary a lot from run to run even if the
settings don't change, if the model uses random numbers. If you want to run the model more
than once at each combination of settings, enter a higher number.
Measure runs using these reporters: This is where you specify what data you want to
collect from each run. For example, if you wanted to record how the population of turtles rose
and fell during each run, you would enter:
count turtles
You can enter one reporter, or several, or none at all. If you enter several, each reporter must
be on a line by itself, for example:
count frogs
count mice
count birds
If you don't enter any reporters, the runs will still take place. This is useful if you want to
record the results yourself your own way, such as with the export-world command.
Measure runs at every step: Normally NetLogo will measure model runs at every step,
using the reporters you entered in the previous box. If you're doing very long model runs, you
might not want all that data. Uncheck this box if you only want to measure each run after it
ends.
Setup commands: These commands will be used to begin each model run. Typically, you
will enter the name of a procedure that sets up the model, typically setup. But it is also
possible to include other commands as well.
Go commands: These commands will be run over and over again to advance to the model
to the next "step". Typically, this will be the name of a procedure, such as go, but you may
include any commands you like.
Stop condition: This lets you do model runs of varying length, ending each run when a
certain condition becomes true. For example, suppose you wanted each run to last until there
were no more turtles. Then you would enter:
not any? turtles
If you want the length of runs to all be of a fixed length, just leave this blank.
The run may also stop because the go commands use the stop command, in the same way
that stop can be used to stop a forever button. The stop command may be used directly in the
go commands, or in a procedure called directly by the go commands. (The intent is that the
same go procedure should work both in a button and in a BehaviorSpace experiment.) Note
that the step in which stop is used is considered to have been aborted, so no results will be
recorded for that step. Therefore, the stopping test should be at the beginning of the go
commands or procedure, not at the end.
Final commands: These are any extra commands that you want run once, when the run
ends. Usually this is left blank, but you might use it to call the export-world command or
record the results of the run in some other way.
Time limit: This lets you set a fixed maximum length for each run. If you don't want to set any
maximum, but want the length of the runs to be controlled by the stop condition instead, enter
0.
Special primitives for BehaviorSpace experiments
Currently there are only two, behaviorspace-run-number and behaviorspace-experiment-name.
The run number reported by the former primitive matches the run number used in the results
files generated by BehaviorSpace. The experiment name reported by the latter matches the
name with which the experiment was set up.
Running an experiment
When you're done setting up your experiment, press the "OK" button, followed by the "Run"
button. A dialog titled "Run options" will appear.
Run options: formats
The run options dialog lets you select the formats you would like the data from your
experiment saved in. Data is collected for each run or step, according to the setting of
Measure runs at every step option. In either case, the initial state of the system is recorded,
after the setup commands run but before the go commands run for the first time.
Table format lists each interval in a row, with each metric in a separate column. Table data is
written to the output file as each run completes. Table format is suitable for automated
processing of the data, such as importing into a database or a statistics package.
Spreadsheet format calculates the min, mean, max, and final values for each metric, and then
lists each interval in a row, with each metric in a separate column. Spreadsheet data is more
human-readable than Table data, especially if imported into a spreadsheet application.
(Note however that spreadsheet data is not written to the results file until the experiment
finishes. Since spreadsheet data is stored in memory until the experiment is done, very large
experiments could run out of memory. So you should disable spreadsheet output unless you
really want it. If you do want spreadsheet output, note that if anything interrupts the
experiment, such as a runtime error, running out of memory, or a crash or power outage, no
spreadsheet results will be written. For long experiments, you may want to also enable table
format as a precaution so that if something happens and you get no spreadsheet output you'll
at least get partial table output.)
After selecting your output formats, BehaviorSpace will prompt you for the name of a file to
save the results to. The default name ends in ".csv". You can change it to any name you want,
but don't leave off the ".csv" part; that indicates the file is a Comma Separated Values (CSV)
file. This is a plain-text data format that is readable by any text editor as well as by most
popular spreadsheet and database programs.
Run options: parallel runs
The run options dialog also lets you select whether you want multiple model runs to happen in
parallel, and if so, how many are allowed to be simultaneously active. This number will default
to the number of processor cores in your computer.
There are a few cautions associated with parallel runs.
First, if multiple runs are active, only one of them will be in the "foreground" and cause the
view and plots to update. The other runs will happen invisibly in the background.
Second, invisible background runs can't use primitives that only work in the GUI. For
example, a background run can't make a movie.
Third, since parallel runs progress independently of each other, table format output may
contain interleaved, out-of-order results. When you analyze your table data, you may wish to
sort it by run number first. (Spreadsheet format output is not affected by this issue, since it is
not written until the experiment completes or is aborted.)
Fourth, using all available processor cores may make your computer slow to use for other
tasks while the experiment is running.
Fifth, doing runs in parallel will multiply the experiment's memory requirements accordingly.
You may need to increase NetLogo's memory ceiling (see this FAQ entry).
Observing runs
After you complete the run options dialog, another dialog will appear, titled "Running
Experiment". In this dialog, you'll see a progress report of how many runs have been
completed so far and how much time has passed. If you entered any reporters for measuring
the runs, and if you left the "Measure runs at every step" box checked, then you'll see a plot of
how they vary over the course of each run.
You can also watch the runs in the main NetLogo window. (If the "Running Experiment" dialog
is in the way, just move it to a different place on the screen.) The view and plots will update as
the model runs. If you don't need to see them update, then use the checkboxes in the
"Running Experiment" dialog to turn the updating off. This will make the experiment go faster.
If you want to stop your experiment before it's finished, press the "Abort" button. Any results
generated so far will still be saved.
When all the runs have finished, the experiment is complete.
Advanced usage
Running from the command line
It is possible to run BehaviorSpace experiments "headless", that is, from the command line,
without any graphical user interface (GUI). This is useful for automating runs on a single
machine or a cluster of machines.
No Java programming is required. Experiment setups can be created in the GUI and then run
later from the command line, or, if you prefer, you can create or edit experiment setups
directly using XML.
How to use it
Run Java with the org.nlogo.headless.Main class. The Main.main() method supports these
arguments:
--model : pathname of model to open (required)
--setup-file : read experiment setups from this file instead of the model file
--experiment : name of experiment to run
--table : pathname to send table output to (or - for standard output)
--spreadsheet : pathname to send table output to (or - for standard output)
--threads : use this many threads to do model runs in parallel, or 1 to disable
parallel runs. defaults to one thread per processor.
--min-pxcor : override world size setting in model file
--max-pxcor : override world size setting in model file
--min-pycor : override world size setting in model file
--max-pycor : override world size setting in model file
is required. If you don't specify --experiment , you must specify --setup-file . By
default no results are generated, so you'll usually want to specify either --table or -spreadsheet, or both. If you specify any of the world dimensions, you must specify all four.
--model
Examples
It is easiest if you create your experiment setup ahead of time in the GUI, so it is saved as
part of the model. To run an experiment setup saved in a model, here is an example
command line:
java -Xmx1024m -Dfile.encoding=UTF-8 -cp NetLogo.jar \
org.nlogo.headless.Main \
--model Fire.nlogo \
--experiment experiment1 \
--table -
(For this to work, NetLogo.jar must be present along with the lib subdirectory containing
necessary libraries. Both NetLogo.jar and lib are included with NetLogo.)
After the named experiment has run, the results are sent to standard output in table format,
as CSV. ("-" is how you specify standard output instead of output to a file.)
When running the headless.Main class as an application, it forces the system property
java.awt.headless to be true. This tells Java to run in headless mode, allowing NetLogo to
run on machines when a graphical display is not available.
Note the use of -Xmx to specify a maximum heap size of one gigabyte. If you don't specify a
maximum heap size, you will get your VM's default size, which may be unusably small. (One
gigabyte is an arbitrary size which should be more than large enough for most models; you
can specify a different limit if you want.)
Note the use of -Dfile.encoding=UTF-8. This forces all file I/O to use UTF-8 encoding. Doing
so ensures that NetLogo can load all models consistently, and that file-* primitives work
consistently on all platforms, including models containing Unicode characters.
The required --model argument is used to specify the model file you want to open.
The --experiment argument is used to specify the name of the experiment you want to run.
(At the time you create an experiment setup in the GUI, you assign it a name.)
Here's another example that shows some additional, optional arguments:
java -Xmx1024m -Dfile.encoding=UTF-8 -cp NetLogo.jar \
org.nlogo.headless.Main \
--model Fire.nlogo \
--experiment experiment2 \
--max-pxcor 100 \
--min-pxcor -100 \
--max-pycor 100 \
--min-pycor -100
Note the use of the optional --max-pxcor, --max-pycor, etc. arguments to specify a different
world size than that saved in the model. (It's also possible for the experiment setup to specify
values for the world dimensions; if they are specified by the experiment setup, then there is
no need to specify them on the command line.)
Since neither --table nor --spreadsheet is specified, no results will be generated. This is useful
if the experiment setup generates all the output you need by some other means, such as
exporting world files or writing to a text file.
Yet another example:
java -Xmx1024m -Dfile.encoding=UTF-8 -cp NetLogo.jar \
org.nlogo.headless.Main \
--model Fire.nlogo \
--experiment experiment2 \
--table table-output.csv \
--spreadsheet spreadsheet-output.csv
The optional --table argument specifies that output should be generated in a
table format and written to the given file as CSV data. If - is specified as the filename, than
the output is sent to the standard system output stream. Table data is written as it is
generated, with each complete run.
The optional --spreadsheet argument specified that spreadsheet output should
be generated and written to the given file as CSV data. If - is specified as the filename, than
the output is sent to the standard system output stream. Spreadsheet data is not written out
until all runs in the experiment are finished.
Note that it is legal to specify both --table and --spreadsheet , and if you do, both kinds of
output file will be generated.
Here is one final example that shows how to run an experiment setup which is stored in a
separate XML file, instead of in the model file:
java -Xmx1024m -Dfile.encoding=UTF-8 -cp NetLogo.jar \
org.nlogo.headless.Main \
--model Fire.nlogo \
--setup-file fire-setups.xml \
--experiment experiment3
If the XML file contains more than one experiment setup, it is necessary to use the -experiment argument to specify the name of the setup to use.
In order to run any of these experiments in 3D add -Dorg.nlogo.is3d=true to any of these
startup commands, for example:
java -Dorg.nlogo.is3d=true -Xmx1024m -Dfile.encoding=UTF-8 -cp NetLogo.jar \
org.nlogo.headless.Main \
--model Fire3D.nlogo \
--experiment experiment1 \
--table -
Note that you should supply a 3D model and there are also 3D arguments --max-pzcor
and --min-pzcor .
The next section has information on how to create standalone experiment setup files using
XML.
Setting up experiments in XML
We don't yet have detailed documentation on authoring experiment setups in XML, but if you
already have some familiarity with XML, then the following pointers may be enough to get you
started.
The structure of BehaviorSpace experiment setups in XML is determined by a Document
Type Definition (DTD) file. The DTD is stored in NetLogo.jar, as system/behaviorspace.dtd.
(JAR files are also zip files, so you can extract the DTD from the JAR using Java's "jar" utility
or with any program that understands zip format.)
The easiest way to learn what setups look like in XML, though, is to author a few of them in
BehaviorSpace's GUI, save the model, and then examine the resulting .nlogo file in a text
editor. The experiment setups are stored towards the end of the .nlogo file, in a section that
begins and ends with a experiments tag. Example:
setupgonot any? firesburned-trees
In this example, only one experiment setup is given, but you can put as many as you want
between the beginning and ending experiments tags.
Between looking at the DTD, and looking at examples you create in the GUI, it will hopefully
be apparent how to use the tags to specify different kind of experiments. The DTD specifies
which tags are required and which are optional, which may be repeated and which may not,
and so forth.
When XML for experiment setups is included in a model file, it does not begin with any XML
headers, because not the whole file is XML, only part of it. If you keep experiment setups in
their own file, separate from the model file, then the extension on the file should be .xml not
.nlogo, and you'll need to begin the file with proper XML headers, as follows:
The second line must be included exactly as shown. In the first line, you may specify a
different encoding than UTF-8, such as UTF-8.
Controlling API
If BehaviorSpace is not sufficient for your needs, a possible alternative is to use our
Controlling API, which lets you write Java code that controls NetLogo. The API lets you run
BehaviorSpace experiments from Java code, or, you can write custom code that controls
NetLogo more directly to do BehaviorSpace-like things. See the Controlling section of the
User Manual for further details on both possibilities.
System Dynamics Guide
This guide has three parts:
What is the System Dynamics Modeler?: A general description of the tool, including the ideas and
principles behind it.
How It Works: Describes the interface and how you use it.
Tutorial: Wolf-Sheep Predation (aggregate): Walks you through creating a model with the System
Dynamics Modeler.
What is the NetLogo System Dynamics Modeler?
System Dynamics is a type of modeling where you try to understand how things relate to one another. It is a little
different from the agent-based approach we normally use in NetLogo models.
With the agent-based approach we usually use in NetLogo, you program the behavior of individual agents and
watch what emerges from their interaction. In a model of Wolf-Sheep Predation, for example, you provide rules
for how wolves, sheep and grass interact with each other. When you run the simulation, you watch the emergent
aggregate-level behavior: for example, how the populations of wolves and sheep change over time.
With the System Dynamics Modeler, you don't program the behavior of individual agents. Instead, you program
how populations of agents behave as a whole. For example, using System Dynamics to model Wolf-Sheep
Predation, you specify how the total number of sheep would change as the total number of wolves goes up or
down, and vice versa. You then run the simulation to see how both populations change over time.
The System Dynamics Modeler allows you to draw a diagram that defines these populations, or "stocks", and
how they affect each other. The Modeler reads your diagram and generates the appropriate NetLogo code -global variables, procedures and reporters -- to run your System Dynamics model inside of NetLogo.
Basic Concepts
A System Dynamics diagram is made of four kinds of elements: Stocks, Variables, Flows and Links.
A Stock is a collection of stuff, an aggregate. For example, a Stock can represent a population of sheep, the
water in a lake, or the number of widgets in a factory.
A Flow brings things into, or out of a Stock. Flows look like pipes with a faucet because the faucet controls how
much stuff passes through the pipe.
A Variable is a value used in the diagram. It can be an equation that depends on other Variables, or it can be a
constant.
A Link makes a value from one part of the diagram available to another. A link transmits a number from a
Variable or a Stock into a Stock or a Flow.
The System Dynamics Modeler figures out how the value of your Stocks change over time by estimating them
over and over. The estimation isn't always perfect, but you can affect its accuracy by changing the value of dt. As
dt decreases, you estimate the model more frequently, so it gets more accurate. However, decreasing dt also
makes the model slower.
Sample Models
There are four basic models in the Sample Models section of the NetLogo Models Library that demonstrate the
use of the System Dynamics Modeler. All four basic models explore population growth (and, in models with
predation, population decline).
Exponential Growth and Logistic Growth are simple examples of growth in one stock.
Wolf Sheep Predation (System Dynamics) is an example of a system with multiple stocks influencing one
another. It models a predator-prey ecosystem using the System Dynamics Modeler.
Wolf Sheep Predation (Docked Hybrid) is an example of a model that runs both the a System Dynamics model
and an agent-based model side-by-side. It runs the System Dynamics implementation of Wolf-Sheep Predation
next to the agent-based Wolf Sheep Predation model from the Biology section of Sample Models.
How it Works
To open the System Dynamics Modeler, choose the System Dynamics Modeler item in the Tools menu. The
System Dynamics Modeler window will appear.
Diagram Tab
The Diagram tab is where you draw your System Dynamics diagram.
The toolbar contains buttons to edit, delete and create items in your diagram.
Creating Diagram Elements
A System Dynamics diagram is made up of four kinds of components: Stocks, Variables, Flows and Links.
Stock
To create a Stock, press the Stock button in the toolbar and click in the diagram area below. A new Stock
appears. Each Stock requires a unique name, which becomes a global variable. Stocks also require an
Initial value. It can be a number, a variable, a complex NetLogo expression, or a call to a NetLogo reporter.
Variable
To create a Variable, press the Variable button and click on the diagram. Each Variable in the System
Dynamics Model requires a unique name, which becomes the name of a procedure, or a global variable.
Variables also require an Expression. This expression can be a number, a variable, a complex NetLogo
expression, or a call to a NetLogo reporter.
Flow
To create a Flow, press the Flow button. Click and hold where you want the Flow to begin -- either on a
Stock or in an empty area -- and drag the mouse to where you want the Flow to end -- on a Stock or in an
empty area. Each Flow requires a unique name, which becomes a NetLogo reporter. Flows require an
Expression, which is the rate of flow from the input to the output. This expression can be a number, a
variable, a complex NetLogo expression, or a call to a NetLogo reporter. If the value is negative, the flow is
in the opposite direction.
When more than one Flow is connected to a Stock, it is important to consider how they should interact with
one another. NetLogo will not enforce that the Flows out of a stock occur in any particular order. Also,
NetLogo will not ensure that the sum of Flows out of a Stock are less than or equal to the value of the
Stock. These behaviors can be implemented explicitly when creating the Expression for a Flow.
For example, if the Flow is defined as a constant value, 10, you can ensure it never draws more than the
value of the Stock by using the min primitive: min (list stock 10). If I want Flow A to deplete a Stock
before Flow B is calculated, I can link Flow A to Flow B and modify Flow B to subtract Flow A's value from
the stock: min (list (max (list 0 (stock - flow-a))) 10) .
Link
To create a Link, click and hold on the starting point for the link -- a Variable, Stock or Flow -- and drag the
mouse to the destination Variable or Flow.
Working with Diagram Elements
When you create a Stock, Variable, or Flow, you see a red question-mark on the element. The question-mark
indicates that the element doesn't have a name yet. The red color indicates that the Stock is incomplete: it's
missing one or more values required to generate a System Dynamics model. When a diagram element is
complete, the name turns black.
Selecting: To select a diagram element, click on it. To select multiple elements, hold the shift key. You can also
select one or more elements by dragging a selection box.
Editing: To edit a diagram element, select the element and press the "Edit" button on the toolbar. Or just doubleclick the element. (You can edit Stocks, Flows and Variables, but you can't edit Links).
Moving: To move a diagram element, select it and drag the mouse to a new location.
Editing dt
On the right side of the toolbar is the default dt, the interval used to approximate the results of your System
Dynamics model. To change the value of the default dt for your aggregate model, press the Edit button next to
the dt display and enter a new value.
Errors
When you click the "check" button or when you edit a stock, flow, or variable the modeler will automatically
generate the NetLogo code the corresponds to your diagram and try to compile that code. If there is an error the
Code tab will turn red and a message will appear, and the portion of the generated code that is causing the
trouble will be highlighted.
This should give you a better idea which element in the diagram is causing the problem.
Code Tab
The System Dynamics Modeler generates NetLogo variables and procedures based on the contents of your
diagram. These procedures are what make the diagram actually perform calculations. The Code tab in the
System Dynamics Modeler window displays the NetLogo procedures generated from your diagram.
You can't edit the contents of the Code tab. To modify your System Dynamics mode, edit the diagram.
Let's take a closer look at how the generated code relates to the diagram.:
Stocks correspond to a global variable that is initialized to the value or expression you provided in the
Initial value field. Each Stock will be updated every step based on the Flows in and out.
Flows correspond to a procedure that contains the expression you provided in the Expression field.
Variables can either be global variables or procedures. If the Expression you provided is a constant it will
be a global variable and initialized to that value. If you used a more complicated Expression to define the
Variable it will create a procedure like a Flow.
The variables and procedures defined in this tab are accessible in the main NetLogo window, just like the
variables and procedures you define yourself in the main NetLogo Code tab. You can call the procedures from
the main Code tab, from the Command Center, or from buttons in the Interface tab. You can refer to the global
variables anywhere, including in the main Code tab and in monitors.
There are three important procedures to notice: system-dynamics-setup, system-dynamics-go , and systemdynamics-do-plot.
initializes the aggregate model. It sets the value of dt, calls reset-ticks, and initializes
your stocks and your converters. Converters with a constant value are initialized first, followed by the stocks with
constant values. The remaining stocks are initialized in alphabetical order.
system-dynamics-setup
runs the aggregate model for dt time units. It computes the values of Flows and Variables
and updates the value of Stocks. It also calls tick-advance with the value of dt. Converters and Flows with nonconstant Expressions will be calculated only once when this procedure is called, however, their order of
evaluation is undefined
system-dynamics-go
plots the values of Stocks in the aggregate model. To use this, first create a plot in the
main NetLogo window. You then need to define a plot pen for each Stock you want to be plotted. This procedure
will use the current plot, which you can change using the set-current-plot command.
system-dynamics-do-plot
The System Dynamics Modeler and NetLogo
The diagram you create with the System Dynamics Modeler, and the procedures generated from your diagram,
are part of your NetLogo model. When you a save the NetLogo model, your diagram is saved with it, in the same
file.
Tutorial: Wolf-Sheep Predation
Let's create a model of Wolf-Sheep Predation with the System Dynamics Modeler.
Step 1: Sheep Reproduction
Open a new model in NetLogo.
Launch the System Dynamics Modeler in the Tools menu.
Our model will have a population of wolves and a population of sheep. Let's start with the sheep. First, create a
Stock that holds a population of Sheep.
Press the Stock button in the toolbar.
Click in the diagram area.
You see a Stock with a red question-mark in the middle.
Double-click the Stock to edit.
Name the stock sheep
Set the initial value to 100.
Deselect the Allow Negative Values checkbox. It doesn't make sense to have negative sheep!
Our sheep population can increase if new sheep are born. To add this to our diagram, we create a Flow into the
stock of sheep.
Click on the Flow button in the toolbar and press the mouse button in an empty area to the left
of the sheep Stock. Drag the Flow to the right until it connects to the sheep Stock and let go.
Edit the Flow and name it sheep-births .
For now, enter a constant, such as 1, into the Expression field.
The number of sheep born during a period of time depends on the number of sheep that are alive: more sheep
means more reproduction.
Draw a Link from the sheep Stock to the sheep-births Flow.
The rate of sheep births also depends on some constant factors that are beyond the scope of this model: the
rate of reproduction, etc.
Create a Variable and name it sheep-birth-rate. Set its value to 0.04
Draw a Link from the sheep-birth-rate Variable to the sheep-births .
Your diagram should look something like this:
Our diagram has the correct structure but we aren't yet finished because it the amount of sheep flowing into the
stock doesn't depend upon the number of sheep and sheep birth rate.
Edit the sheep-births Flow and set the expression to sheep-birth-rate * sheep .
We now have a complete diagram. To see the NetLogo code generated by our diagram, you can click on the
Code tab of the System Dynamics Modeler window. It looks like this:
Step 2: NetLogo Integration
Once you create an aggregate model with the System Dynamics Modeler, you can interact with the model
through the main NetLogo interface window. Let's build our NetLogo model to run the code generated by our
diagram. We'll need a setup and go buttons which call the system-dynamics-setup and system-dynamics-go
procedures created by the System Dynamics Modeler. And we'll want a monitor and a plot to watch the changes
in sheep population.
Select the main NetLogo window
In the Code tab, write:
to setup
ca
system-dynamics-setup
end
to go
system-dynamics-go
system-dynamics-do-plot
end
Move to the Interface tab
Create a setup button
Create a go button (don't forget to make it forever)
Create a sheep monitor.
Create a plot called "populations" with a pen named "sheep".
Now we're ready to run our model.
Press the setup button.
Don't press the "go" button yet. Instead, type go four or five times into the Command Center
Notice what happens. The sheep population increases exponentially. After four or five iterations, we have an
enormous number of sheep. That's because we have sheep reproduction, but our sheep never die.
To fix that, let's finish our diagram by introducing a population of wolves which eat sheep.
Step 3: Wolf Predation
Move back to the System Dynamics window
Add a stock of wolves
Add Flows, Variables and Links to make your diagram look like this:
Add one more Flow from the wolves Stock to the Flow that goes out of the Sheep stock.
Fill in the names of the diagram elements so it looks like this:
where
initial-value of wolves is 30,
wolf-deaths is wolves * wolf-death-rate ,
wolf-death-rate is 0.15,
predator-efficiency is .8 ,
wolf-births is wolves * predator-efficiency * predation-rate * sheep,
predation-rate is 3.0E-4,
and sheep-deaths is sheep * predation-rate * wolves.
Adjust the dt of the system dynamics model by selecting "Edit" next to dt in the toolbar of the
system dynamics modeler. In the dialog that appears, enter 0.01.
Now we're really done.
Go back to the main NetLogo window
Add a plot pen named "wolves" to the population plot
Press setup and go to see your System Dynamics Modeler diagram in action.
You see a plot of the populations that looks like this:
HubNet Guide
This section of the User Manual introduces the HubNet system and includes instructions to
set up and run a HubNet activity.
HubNet is a technology that lets you use NetLogo to run participatory simulations in the
classroom. In a participatory simulation, a whole class takes part in enacting the behavior of a
system as each student controls a part of the system by using an individual device, such as a
networked computer.
For example, in the Gridlock simulation, each student controls a traffic light in a simulated city.
The class as a whole tries to make traffic flow efficiently through the city. As the simulation
runs, data is collected which can afterwards be analyzed on a computer.
For more information on participatory simulations and their learning potential, please visit the
Participatory Simulations Project web site.
Understanding HubNet
NetLogo
NetLogo is a programmable modeling environment. It comes with a large library of existing
simulations, both participatory and traditional, that you can use and modify. Content areas
include social science and economics, biology and medicine, physics and chemistry, and
mathematics and computer science. You and your students can also use it to build your own
simulations.
In traditional NetLogo simulations, the simulation runs according to rules that the simulation
author specifies. HubNet adds a new dimension to NetLogo by letting simulations run not just
according to rules, but by direct human participation.
Since HubNet builds upon NetLogo, we recommend that before trying HubNet for the first
time, you become familiar with the basics of NetLogo. To get started using NetLogo models,
see Tutorial #1: Running Models in the NetLogo Users Manual.
HubNet Architecture
HubNet simulations are based on a client/server architecture. The activity leader uses the
NetLogo application to run a HubNet activity. When NetLogo is running a HubNet activity, we
refer to it as a HubNet server. Participants use a client application to log in and interact with
the HubNet server.
While HubNet is only supported via the Java Desktop clients at the moment, we hope to add
support for other types of clients such as tablets and phones in the future.
Computer HubNet
Activities
The following activities are available in the Models Library, in the HubNet Activities folder.
Information on how to run the models and activities can be found in the Info tab of each
model. Additional discussion of educational goals and ways to incorporate many of the
activities into your classroom in the Participatory Simulations Guide on the Participatory
Simulations Project web site.
Bug Hunters Camouflage - students hunt bugs and camouflaging emerges.
Dice Stalagmite HubNet - students roll dice and explore the space of dependent and
independent events.
Disease - A disease spreads through the simulated population of students.
Disease Doctors - A slight modification to the Disease activity where some students can
recover from the disease.
Gridlock - Students use traffic lights to control the flow of traffic through a city.
Polling - Ask students questions and plot their answers.
Root Beer Game - An adaptation of a popular game created at MIT in the early 1960s
that shows how small delays in a distribution system can create big problems.
Sampler - Students engage in statistical analysis as individuals and as a classroom.
Through these activities, students discover the meaning and use of basic concepts in
statistics.
Tragedy of the Commons - Students work as farmers sharing a common resource.
Clients
To use the client application you simply need to launch the HubNet client application that is
bundled with NetLogo.
Requirements
To use Computer HubNet, you need a networked computer with NetLogo installed for the
server. When using the client application you will also need a networked computer with
NetLogo installed for each participant. When using in classroom settings we also suggest an
attached projector for the leader to project the entire simulation to the participants.
Starting an activity
You'll find the HubNet activities in NetLogo's Models Library, in the HubNet Activities folder.
We suggest doing a few practice runs of an activity before trying it in front of a class.
Open a Computer HubNet model. NetLogo will prompt you to enter the name of your new
HubNet session. This is the name that participants will use to identify this activity. Enter a
name and press Start.
NetLogo will open the HubNet Control Center, which lets you interact with the HubNet server.
You, as the leader, should then notify everyone that they may join. To join the activity,
participants launch the HubNet Client application and enter their name. They should see your
activity listed and can join your activity by selecting it and pressing Enter. If the activity you
started is not listed the student can enter the server address manually which can be found in
the HubNet Control Center.
HubNet Control Center
The HubNet Control Center lets you interact with the HubNet server. It displays the name,
activity, address and port number of your server. The "Mirror 2D View on clients" checkbox
controls whether the HubNet participants can see the view on their clients, assuming there is
a view in the client setup. The "Mirror plots on clients" checkbox controls whether participants
will receive plot information.
The client list on the right displays the names of clients that are currently connected to you
activity. To remove a participant from the activity, select their name in the list and press the
Kick button. To launch your own HubNet client press the Local button, this is particularly
useful when you are debugging an activity. The "Reset" button kicks out all currently logged in
clients and reloads the client interface.
The lower part of the Control Center displays messages when a participant joins or leaves the
activity. To broadcast a message to all the participants, click on the field at the bottom, type
your message and press Broadcast Message.
Troubleshooting
I started a HubNet activity, but when participants open a HubNet Client, my
activity isn't listed.
On some networks, the HubNet Client cannot automatically detect a HubNet server. Tell your
participants to manually enter the server address and port of your HubNet server, which
appear in the HubNet Control Center.
Note: The technical details on this are as follows. In order for the client to detect the server,
multicast routing must be available between them. Not all networks support multicast routing.
In particular, networks that use the IPsec protocol typically do not support multicast. The IPsec
protocol is used on many virtual private networks (VPNs).
When a participant tries to connect to an activity, nothing happens (the client
appears to hang or gives an error saying that no server was found).
If your computer or network has a firewall, it may be impeding the HubNet server from
communicating. Make sure that your computer and network are not blocking ports used by
the HubNet server (ports 9173-9180).
The view on the HubNet client is gray.
Verify that the "Mirror 2D view on clients" checkbox in the HubNet Control Center is
selected.
Make sure that the display switch in the model is on.
If you have made changes to the size of the view on the server you may need to press
the "Reset" button in the Control Center to ensure the clients get the new size.
There is no view on the HubNet client.
Some activities don't have a view on the client. If you want to add a view simply select
"HubNet Client Editor" from the Tools Menu and add a view like any other widget. Make sure
to press the "Reset" button before having clients log in.
I can't quit a HubNet client.
You will have to force the client to quit. On OS X, force quit the application by selecting Force
Quit... in the Apple menu. On Windows, press Ctrl-Alt-Delete to open the Task Manager,
select HubNet Client and press End Task.
My computer went to sleep while running a HubNet activity. When I woke the
computer up, I got an error and HubNet wouldn't work anymore.
The HubNet server may stop working if the computer goes to sleep. If this happens, quit the
NetLogo application and start over. Change the settings on your computer so it won't sleep
again.
My problem is not addressed on this page.
See Contacting Us.
Known Limitations
If HubNet malfunctions, see the bug reporting information at Contacting Us.
Please note that:
HubNet has not yet been extensively tested with large numbers of clients (i.e. more than
about 25). Unexpected results may occur with more clients.
Out-of-memory conditions are not handled gracefully
Sending large amounts of plotting messages to the clients can take a long time.
NetLogo does not handle malicious clients in a robust manner (in other words, it is likely
vulnerable to denial-of-service type attacks).
Performance does not degrade gracefully over slow or unreliable network connections.
If you are on a wireless network or sub-LAN, the IP address in the HubNet Control
Center is not always the entire IP address of the server.
Computer HubNet has only been tested on LANs, and not on dial-up connections or
WANs.
Teacher workshops
For information on upcoming workshops and NetLogo and HubNet use in the classroom,
please contact us.
HubNet Authoring Guide
To learn about authoring or modifying HubNet activities, see the HubNet Authoring Guide.
Running HubNet in headless mode
To learn about running HubNet activities from the command line, with no GUI on the server,
see the HubNet section in the Controlling Guide.
Getting help
If you have any questions about HubNet or need help getting started, contact us.
HubNet Authoring Guide
This guide shows how to understand and modify the code of existing HubNet activities and
write your own new ones. It assumes you are familiar with running HubNet activities, basic
NetLogo code and NetLogo interface elements. For more general information about HubNet
see the HubNet Guide.
Coding HubNet activities
Setup
Receiving information from clients
Sending information to clients
Examples
How to make a client interface
View updates on the clients
Clicking in the view on clients
Customizing the client's view
Plot updates on the clients
Coding HubNet activities
Many HubNet activities will share bits of the same code. That is the code that it used to setup
the network and the code that is used to receive information from and send information to the
clients. If you understand this code you should be able to easily make modifications to
existing activities and you should have a good start on writing your own activities. To get you
started we have provided a Template model (in HubNet Activities -> Code Examples) that
contains the most basic components that will be in the majority of HubNet activities. You
should be able to use this activity as a starting point for most projects.
Code Example: Template
Setup
To make a NetLogo model into a HubNet activity you must first initialize the network. In most
HubNet activities you will use the startup procedure to initialize the network. startup is a
special procedure that NetLogo runs automatically when you open any model. That makes it a
good place to put code that you want to run once and only once (no matter how many times
the user runs the model). For HubNet we put the command that initializes the network in
startup because once the network is setup we don't need to do so again. We initialize the
system using hubnet-reset , which will ask the user for a session name and open up the
HubNet Control Center. Here is the startup procedure in the template model:
to startup
hubnet-reset
end
Now that the network is all setup you don't need to worry about calling hubnet-reset again.
Take a look at the setup procedure in the template model:
to setup
cp
cd
clear-output
ask turtles
[
set step-size 1
hubnet-send user-id "step-size" step-size
]
end
For the most part it looks like most other setup procedures, however, you should notice that it
does not call clear-all. In this model, and in the great majority of HubNet activities in the
Models Library, we have a breed of turtles that represent the currently logged in clients. In this
case we've called this breed students. Whenever a client logs in we create a student and
record any information we might need later about that client in a turtle variable. Since we don't
want to require users to log out and log back in every time we setup the activity we don't want
to kill all the turtles, instead, we want to set all the variables back to initial values and notify
the clients of any changes we make (more on that later).
Receiving messages from clients
During the activity you will be transferring data between the HubNet clients and the server.
Most HubNet activities will call a procedure in the go loop that checks for new messages from
clients in this case it's called listen clients:
to listen-clients
while [ hubnet-message-waiting? ]
[
hubnet-fetch-message
ifelse hubnet-enter-message?
[ create-new-student ]
[
ifelse hubnet-exit-message?
[ remove-student ]
[ execute-command hubnet-message-tag ]
]
]
end
As long as there are messages in the queue this loop fetches each message one at a time.
hubnet-fetch-message makes the next message in the queue the current message and sets
the reporters hubnet-message-source, hubnet-message-tag, and hubnet-message to the
appropriate values. The clients send messages when the users login and logout any time the
user manipulates one of the interface elements, that is, pushes a button, moves a slider,
clicks in the view, etc. We step through each message and decide what action to take
depending on the type of message (enter, exit, or other), the hubnet-message-tag (the name
of the interface element), and the hubnet-message-source of the message (the name of the
client the message came from).
On an enter message we create a turtle with a user-id that matches the hubnet-messagesource which is the name that each user enters upon entering the activity, it is guaranteed to
be unique.
to create-new-student
create-students 1
[
set user-id hubnet-message-source
set label user-id
set step-size 1
send-info-to-clients
]
end
At this point we set any other client variables to default values and send them to the clients if
appropriate. We declared a students-own variable for every interface element on the client that
holds state, that is, anything that would be a global variable on the server, sliders, choosers,
switches and input boxes. It is important to make sure that these variables stay synchronized
with the values visible on the client.
When the clients logout they send an exit message to the server which gives you a chance to
clean up any information you have been storing about the client, in this case we merely have
to ask the appropriate turtle to die.
to remove-student
ask students with [user-id = hubnet-message-source]
[ die ]
end
All other messages are interface elements identified by the hubnet-message-tag which is the
name that appears in the client interface. Every time an interface element changes a message
is sent to the server. Unless you store the state of the values currently displayed in the client
interface will not be accessible in other parts of the model. That's why we've declared a
students-own variable for every interface element that has a state (sliders, switches, etc).
When we receive the message from the client we set the turtle variable to the content of the
message:
if hubnet-message-tag = "step-size"
[
ask students with [user-id = hubnet-message-source]
[ set step-size hubnet-message ]
]
Since buttons don't have any associated data there is generally no associated turtle variable,
instead they indicate an action taken by the client, just as with a regular button there is often
procedure associated with each button that you call whenever you receive a message
indicating the button has been pressed. Though it is certainly not required, the procedure is
often a turtle procedure, that is, something that the student turtle associated with the message
source can execute:
if command = "move left"
[ set heading 270
fd 1 ]
Sending messages to clients
As mentioned earlier you can also send values to any interface elements that display
information: monitors, sliders, switches, choosers, and input boxes (note that plots and the
view are special cases that have their own sections).
There are two primitives that allow you to send information hubnet-send and hubnetbroadcast. Broadcast sends the information to all the clients; send sends to one client, or a
selected group.
As suggested earlier, nothing on the client updates automatically. If a value changes on the
server, it is your responsibility as the activity author to update monitors on the client.
For example, say you have a slider on the client called step-size and a monitor called Step
Size (note that the names must be different) you might write updating code like this:
if hubnet-message-tag = "step-size"
[
ask student with [ user-id = hubnet-message-source ]
[
set step-size hubnet-message
hubnet-send user-id "Step Size" step-size
]
]
You can send any type of data you want, numbers, strings, lists, lists of lists, lists of strings,
however, if the data is not appropriate for the receiving interface element (say, if you were to
send a string to a slider) the message will be ignored. Here are a few code examples for
different types of data:
data
type
hubnet-broadcast
example
hubnet-send
example
number
hubnet-broadcast "A" 3.14
hubnet-send "jimmy" "A" 3.14
string
hubnet-broadcast "STR1" "HI THERE"
hubnet-send ["12" "15"] "STR1" "HI
THERE"
list of
hubnet-broadcast "L2" [1 2 3]
numbers
matrix of hubnet-broadcast "[A]" [[1 2] [3
numbers 4]]
list of
strings
hubnet-broadcast "user-names"
[["jimmy" "susie"] ["bob"
"george"]]
hubnet-send hubnet-message-source "L2"
[1 2 3]
hubnet-send "susie" "[A]" [[1 2] [3
4]]
hubnet-send "teacher" "user-names"
[["jimmy" "susie"] ["bob" "george"]]
Examples
Study the models in the "HubNet Activities" section of the Models Library to see how these
primitives are used in practice in the Code tab. Disease is a good one to start with.
How to make a client interface
Open the HubNet Client Editor, found in the Tools Menu. Add any buttons, sliders, switches,
monitors, plots, choosers, or notes that you want just as you would in the interface tab. You'll
notice that the information you enter for each of the widgets is slightly different than in the
Interface panel. Widgets on the client don't interact with the model in the same way. Instead
of a direct link to commands and reporters the widgets send messages back to the server and
the model then determines how those messages affect the model. All widgets on the client
have a tag which is a name that uniquely identifies the widget. When the server receives a
message from that widget the tag is found in hubnet-message-tag
For example, if you have a button called "move left", a slider called "step-size", a switch called
"all-in-one-step?", and a monitor called "Location:", the tags for these interface elements will
be as follows:
interface
element
tag
move left
move left
step-size
step-size
all-in-one-step?
all-in-one-step?
Location:
Location:
Note that you can only have one interface element with a specific name. Having more than
one interface element with the same tag in the client interface will result in unpredictable
behavior since it is not clear which element you intended to send the information to.
View updates on the clients
View mirroring lets views of the world be displayed in clients as well on the server. View
mirroring is enabled using a checkbox in the HubNet Control Center.
When mirroring is enabled, client views update whenever the view on the server does. To
avoid excessive network traffic, the view should not update more often than necessary.
Therefore we strongly recommend using tick-based updates, rather than continuous updates.
See the View Updates section of the Programming Guide for an explanation of the two types
of updates.
With tick-based updates, updates happen when a tick or display command runs. We
recommend using these commands only inside an every block, to limit the frequency of view
updates and thus also limit network traffic. For example:
every 0.1
[
display
]
If there is no View in the clients or if the Mirror 2D View on Clients checkbox in the HubNet
Control Center is not checked, then no view updates are sent to the clients.
Clicking in the view on clients
If the View is included in the client, two messages are sent to the server every time the user
clicks in the view. The first message, when the user presses the mouse button, has the tag
"View". The second message, sent when the user releases the mouse button, has the tag
"Mouse Up". Both messages consist of a two item list of the x and y coordinates. For
example, to turn any patch that was clicked on by the client red, you would use the following
NetLogo code:
if hubnet-message-tag = "View"
[
ask patches with [ pxcor = (round item 0 hubnet-message) and
pycor = (round item 1 hubnet-message) ]
[ set pcolor red ]
]
Customizing the client's view
When view mirroring is enabled, by default clients see the same view the activity leader sees
on the server. But you can change this so that each client sees something different, not just a
literal "mirror".
You can change what a client sees in two distinct ways. We call them "client perspectives"
and "client overrides".
Changing a client's perspective means making it "watch" or "follow" a particular agent, much
like the watch and follow commands that work with ordinary NetLogo models. See the
dictionary entries for hubnet-send-watch , hubnet-send-follow , and hubnet-reset-perspective .
Code Example: Client Perspective Example
Client overrides let you change the appearance of patches, turtles, and links in the client
views. You can override any of the variables affecting an agent's appearance, including the
hidden? variable causing a turtle or link to be visible or invisible. See the dictionary entries for
hubnet-send-override, hubnet-clear-override, and hubnet-clear-overrides .
Code Example: Client Overrides Example
Plot updates on the clients
If plot mirroring is enabled (in the HubNet Control Center) and a plot in the NetLogo model
changes and a plot with the exact same name exists on the clients, a message with that
change is sent to the clients causing the client's plot to make the same change. For example,
let's pretend there is a HubNet model that has a plot called Milk Supply in NetLogo and the
clients. Milk Supply is the current plot in NetLogo and in the Command Center you type:
plot 5
This will cause a message to be sent to all the clients telling them that they need to plot a
point with a y value of 5 in the next position of the plot. Notice, if you are doing a lot of plotting
all at once, this can generate a lot of plotting messages to be sent to the clients.
Modeling Commons Guide
Introduction
The Modeling Commons (http://modelingcommons.org/) is a Web-based collaboration system for
NetLogo modelers. Users of the Modeling Commons can share, download, modify, create variations
of, comment on, and run NetLogo models -- both those that are a part of the NetLogo models
library, and also those that have been uploaded by other NetLogo users.
By uploading your NetLogo models to the Modeling Commons, you make it easy for others to see,
review, and comment on your work. You can optionally keep the model private, either to yourself or
to a group of your choice, if you aren't comfortable with letting everyone see the model. You can
always change the permissions associated with a model, if you change your mind later on.
NetLogo now makes it possible to save models to the Modeling Commons, just as you can save
them to .nlogo files on your own computer. You can access this functionality by selecting "Upload to
Modeling Commons" from the "File" menu.
Use of the Modeling Commons is free of charge. You may use it for your own personal work, for
your research group or company, or for a class in which you are a student or teacher. The Modeling
Commons is sponsored by the CCL, the same group that develops and distributes NetLogo.
Modeling Commons Accounts
In order to upload models to the Modeling Commons, you must first be a registered user.
Unregistered users can view and download models, but cannot upload, edit, or comment on them.
The first time that you invoke "Save to Modeling Commons" in NetLogo, you will be prompted to
enter your e-mail address and password. If you already have an account, then you can enter this
information and click on the "Login" button.
If you don't yet have an account with the Modeling Commons, then you will need to create one.
Click on the "Create Account" button, and enter the requested information. Once you have done so,
click on the "Create Account" button. If there are no errors, then you will be prompted to upload a
NetLogo model. Alternatively, you may go to the Modeling Commons itself and register with your
Web browser.
Uploading Models
There are three ways to upload a model to the Modeling Commons: Uploading, updating, and
creating a child ("forking"). The following sections describe these in detail.
Upload A New Model
A new model will be created in the Modeling Commons, with its own page, description, and forum.
You should use this function the first time that you save a model to the Modeling Commons.
You must give your model a name. Model names are not required to be unique; you could have 2 or
more models with the same name, though we recommend that you not do this.
By default, anyone can view, fork, and update your model. You can restrict the ability to view and
fork your model by changing the visibility permission. You can restrict the ability to update your
model by changing the changeability permission. In order to set permissions for multiple people,
assign your model to a group, and then restrict visibility or changeability to members of that group.
Groups can be created from the Modeling Commons. Once you have uploaded your model, you can
edit the permissions from the model's Modeling Commons page.
You can optionally upload a preview image to your model. The preview image will be displayed
alongside your model whenever it is shown on the Modeling Commons. While uploading a preview
image is optional, we highly recommend that you do so, in one of the following three ways:
The "Use current image" option tells NetLogo to use the current view as your preview. We
recommend that you first run the model, such that it shows off the key visual features.
The "Auto-generate image" feature auto-generates a preview image by running random-seed 0
setup repeat 75 [ go ].
This option will only be enabled if you have definedsetup and go
procedures for NetLogo to run.
The "Image from file" feature allows you to upload any PNG image. Preview images work best
when they are square.
Upload A Child Of An Existing Model ("forking")
Saving a model in this way, sometimes known as "forking," does not change or overwrite the
original model. Rather, it creates a new model on the Modeling Commons, much as a plain "save"
would do, simultaneously creating a parent-child relationship between the old model and the new
one. This relationship can be seen on the "family" tab for a given model. You may fork any model for
which you have "view" permissions, including one that you cannot change. You may wish, for
example, to create a variation on a model in the NetLogo models library.
To fork a model, you must give your new child a name, as well as select an existing model to fork.
To indicate the existing model, start typing the name of the model that you would like to fork. Select
its name from among the search results.
Finally, you must enter a description about what you are changing in your child model, and how it
relates to its parent.
Updating An Existing Model
Use this option if you have improved a model that already exists in the Modeling Commons. Existing
attachments, discussions, and social tags will be preserved, but the model that users can display,
run, and download will be updated. You may only update a model for which you have "write"
permissions.
All versions of a model are saved in the Modeling Commons, so you should feel free to experiment
with new ideas. If something goes wrong, you can always refer to an old version from the "history"
tab on a model's page.
To indicate which model should be updated, start typing the name of the model. Select the name
that pops up with the search results. Finally, enter a description about what you are changing in
your new version.
Logging
NetLogo's logging facility allows researchers to record student actions for later analysis.
Logging in NetLogo, once initiated, is invisible to the student. The researcher can choose the
type of events logged through a configuration file.
NetLogo uses the log4j package for logging. If you have previous experience with this package
you'll find logging in NetLogo familiar.
Logging is supported only by the special NetLogo Logging application.
Starting logging
This depends on what operating system you are using.
Mac OS X or Windows
There is a special logging launcher in the NetLogo directory called NetLogo Logging. Double
click on the icon.
On Windows, the NetLogo directory can be found at C:\Program Files, unless you chose a
different location when you installed NetLogo.
Linux and others
To enable logging, invoke the netlogo.sh script as follows:
netlogo.sh --logging netlogo_logging.xml
You could also modify the script to include these flags, or copy the script and modify the copy.
You can replace netlogo_logging.xml with any valid log4j XML configuration file, which will be
discussed in more detail later.
Using logging
When NetLogo starts up it will ask for a user name. This name will appear in all the logs
generated during this session.
Where logs are stored
Logs are stored in the OS-specific temp directory. On most Unix-like systems that is /tmp. On
Windows Vista the logs can be found in c:\Users\\AppData\Local\Temp, where is
the logged in user. On Mac OS X, the temp directory varies for each user. You can determine
your temp directory by opening the Terminal application and typing echo $TMPDIR at the
prompt.
There are two convenience commands that will help you manage the logs. __zip-log-files
filename will gather all the logs in the temp directory and put them in one zip file, at the
location specified. After doing __zip-log-files the existing logs are not deleted, you can do so
explicitly by using __delete-log-files.
The following is a chart describing the name of the loggers available, the type of events each
logs, at what level, and provides a sample output using the XMLLayout. All the loggers are
found in org.nlogo.log.Logger. When referring to the loggers in the configuration file you
should use the fully qualified name. So, for example, the logger GLOBALS would actually be
org.nlogo.log.Logger.GLOBALS
Logger
Events
Level
Example
a global variable info,
changes
debug
FOO51.0
GREENS
sliders,
switches,
choosers, input
boxes are
changed
through the
interface
info
changedfoo51.00.0100.01.0
CODE
code is
compiled,
including:
command
center, Code
tab, slider
bounds, and
buttons
info
compiledcrt 1Osuccess
info
added
info
show 1releasedonce
GLOBALS
a widget is
added or
WIDGETS
removed from
the interface
BUTTONS
a button is
pressed or
released
SPEED
TURTLES
LINKS
the speed slider
changes
turtles die or
are born
links die or are
born
info
0.0
info
turtle 1bornTURTLES
info
link 2 7bornLINKS
How to configure the logging output
The default logging configuration (netlogo_logging.xml) looks something like this:
NetLogo defines 8 loggers, all descend directly from the root logger, which means unless you
explicitly set the properties (appender, layout, and output level) in the configuration they will
inherit them from the root. In the default configuration the root is set to level INFO, the
appender is org.nlogo.log.XMLFileAppender and layout is org.nlogo.log.XMLLayout. Together
these generate a nicely formatted XML file as defined in the netlogo_logging.dtd which is
based on the log4j dtd. If the appender is a FileAppender (including the XMLFileAppender) a
new file is start each time the user opens a model.
This configuration, first defines an appender named "A1" of type XMLFileAppender with an
XMLLayout. The appender defines where the logging data goes, in this case the data goes
into a file. In fact, if NetLogo is given a FileAppender it will automatically start a new file every
time the user opens a new model. The XMLFileAppender also does some formatting and
writes the appropriate headers to the file. The layout defines how to write each individual
message. Unless you are an advanced user there is no need change (or worry about) the
appender or the layout.
At the end of the configuration notice the definition of the root logger. All of the other loggers
descend from the root logger and, thus, inherit the properties of the root unless explicitly set.
This case is fairly simple, having set up the appender A1 we make that the default appender
for the root (and all other loggers) and make the default priority "INFO". Messages that are
logged at the INFO level or higher will be written, messages logged at lower levels will not.
Note that with only one exception NetLogo always logs at level INFO. Sets to globals that don't
change the value of the global are logged at level DEBUG. Which means that these messages
are disabled by default, since debug is lower level than info. The rest of the body of the
configuration file overrides properties of the root logger in a few specific loggers (or categories
as they are known in the configuration file, the terms can be assumed to be synonymous for
the proposes of this document). That is it turns off the WIDGET, TURTLES, and LINKS
loggers, by default. To re-enable them you can changes the priority from off to info, like this:
or you can simply remove the entire reference to the category from the configuration file, as it
is not serving any other purpose.
Advanced Configuration
This is only a basic introduction to configuration files for logging in NetLogo. There are many
more configuration options available through the log4j framework. See the log4j
documentation.
Controlling Guide
NetLogo can be invoked and controlled by another program running on the Java Virtual
Machine. For example, you might want to call NetLogo from a small program that does
something simple like automate a series of model runs. Or, you might want to embed
NetLogo models in a larger application.
For more information, go here.
Mathematica Link
What is it?
The NetLogo-Mathematica link provides modelers with an easy to use, real-time link between
NetLogo and Mathematica. Together, these tools can provide users with a highly interactive,
self-documenting work flow that neither can provide alone.
Mathematica includes many of the tools that agent-based modelers rely on throughout the
research process: advanced import capabilities, statistical functions, data visualization, and
document creation. With the NetLogo-Mathematica link, you can run all of these tools side-byside with NetLogo.
Because all Mathematica documents, or notebooks, contain comments, code, images,
annotations, and interactive objects, the integration of NetLogo and Mathematica provides a
more complete solution for complex model exploration for students and researchers alike.
The basic functionality of the link is much like the NetLogo Controlling API: you can load
models, execute commands, and report back data from NetLogo. Unlike the Controlling API,
which is based on Java, all interactions with the link are interpreted, making it ideal not only
for rapidly designing custom BehaviorSpace-like experiments, but also as a companion to
NetLogo in debugging your model.
For more information about Mathematica, please visit the Wolfram Research web site.
What can I do with it?
Here are a few examples of what you can do with the Mathematica-NetLogo link.
Analyze your model in real-time with seamless two-way data conversion
Develop high quality, custom visualizations of model data
Collect detailed simulation data across large multi-dimensional parameter spaces
Rapidly develop interactive interfaces for exploring model behavior
Have direct access to patches and network data with built-in functions
Installation
The NetLogo-Mathematica link supports Mathematica 10 or greater. To install the NetLogoMathematica link:
Go to the menu bar in Mathematica
Click on File and select Install...
In the Install Mathematica Item dialog
Select Package for Type of item to install
Click Source, and select From file...
In the file browser, go to the location of your NetLogo installation,
click on the Mathematica Link subfolder, and select NetLogo.m.
For Install Name, enter NetLogo.
You can either install the NetLogo link in your user base directory or in the system-wide
directory. If the NetLogo link is installed in the user base directory, other users on the system
must also go through the NetLogo-Mathematica link installation process to use it. This option
might be preferable if you do not have permission to modify files outside of your home
directory. Otherwise, you can install NetLogo-Mathematica link in the system-wide
Mathematica base directory.
Usage
This section will very briefly introduce how to use the NetLogo-Mathematica Link. It will show
you how to load the NetLogo-Mathematica link package, start NetLogo, execute commands,
and retrieve data from NetLogo.
Loading the package: Once the NetLogo-Mathematica link is installed, you can load the
package by entering the following into your Mathematica notebook:
<-at
Since 4.1
turtles-at dx dy dz
-at dx dy dz
3D versions of turtles-at and breeds-at.
Reports an agentset containing the turtles on the patch (dx, dy, dz) from the caller
(including the caller itself if it's a turtle).
;; suppose I have 40 turtles at the origin
show [count turtles-at 0 0 0] of turtle 0
=> 40
world-depth
world-depth
Reports the total depth of the NetLogo world.
The depth of the world is the same as max-pzcor - min-pzcor + 1.
See also max-pzcor, min-pzcor, world-width, and world-height
zcor
Since 4.1
zcor
This is a built-in turtle variable. It holds the current z coordinate of the turtle. This is a
floating point number, not an integer. You can set this variable to change the turtle's
location.
This variable is always greater than or equal to (- screen-edge-z) and strictly less than
screen-edge-z.
See also setxy, xcor, ycor, pxcor, pycor, pzcor
zoom
Since 4.1
zoom number
Move the observer toward the point it is facing, number steps. The observer will never
move beyond the point it is facing so if number is greater than the distance to that point it
will only move as far as the point it is facing.
Extensions Guide
NetLogo allows users to write new commands and reporters in Java and other languages and
use them in their models. This section of the User Manual introduces this facility and shows
how to use an extension in your model once you have obtained or made one.
Extensions created by members of the NetLogo community are available from
https://github.com/NetLogo/NetLogo/wiki/Extensions.
For information on creating your own extensions, go here.
Using Extensions
To use an extension in a model, add the extensions keyword at the beginning of the Code
tab, before declaring any breeds or variables.
After extensions comes a list of extension names in square brackets. For example:
extensions [sound speech]
Using extensions tells NetLogo to find and open the specified extension and makes the
custom commands and reporters found in the extension available to the current model. You
can use these commands and reporters just as if they were built-in NetLogo primitives.
Where extensions are located
NetLogo will look for extensions in several places:
1. In the folder of the current model.
2. The extensions folder located with the NetLogo installation. For typical NetLogo
installations:
On Mac OS X: /Applications/NetLogo 6.0.1/extensions
On 64-bit Windows with 64-bit NetLogo or 32-bit Windows with 32-bit NetLogo:
C:\Program Files\NetLogo 6.0.1\app\extensions
On 64-bit Windows with 32-bit NetLogo: C:\Program Files (x86)\NetLogo
6.0.1\app\extensions
On Linux: the app/extensions subdirectory of the NetLogo directory extracted
the installation .tgz
from
Each NetLogo extension consists of a folder with the same name as the extension, entirely in
lower case. This folder must contain a JAR file with the same name as the folder. For
example the sound extension is stored in a folder called sound with a file inside called
sound.jar.
To install a NetLogo extension for use by any model, put the extension's folder in the NetLogo
extensions directory. Or, you can just keep the extension's folder in the same folder as the
model that uses it.
Some extensions depend on additional files. These files will be in the extension's folder along
with the JAR file. The folder may also contain other files such as documentation and example
models.
NetLogo Arduino Extension
Using
For a first use without compiling code, do the following:
1.
Acquire the NetLogo software. The Arduino extension comes pre-installed with
NetLogo 5.2.1 and later.
2.
Acquire an Arduino board and install the arduino IDE
3.
Use the Arduino IDE to edit the Sketch (if desired) and send to the board. (See
elaborate comments in the sketch for recommendations about what to comment
out/leave in depending on your setup & circuit on the board.)
4.
Once the Arduino has the sketch loaded on it, it will run that sketch whenever it is
powered on.
5.
Open the test “Arduino Example” model in the NetLogo Models library (it’s in the
“IABM Textbook” > “Chapter 8” folder)
6.
Connect the Arduino to a USB port on the computer if it is not still connected from
step 3.
7.
Press OPEN to choose the port to communicate with and establish the connection.
8.
Use the buttons to send byte commands; use the interface to inspect variable
value(s) that your sketch is sending.
9.
Note that by typing arduino:primitives you can get a list of the available commands
in the extension.
Notes
A NetLogo model using this extension must work in conjunction with an Arduino Sketch.
These two endpoints communicate by way of an application protocol that they define. For
example, if the NetLogo model sends a byte ‘1’ over the wire this may mean something to
the Arduino Sketch, which will respond accordingly. The Arduino Sketch for its own part
may send name-value pairs over the serial port, which then can be looked up
asynchronously by the NetLogo model.
The modeler is free to build as simple or as complex an application protocol on top of this
raw communication mechanism.
The asynchronous nature of the board-to-computer communications has one notable
limitation. If you choose to try to simulate a synchronous, BLOCKING READ
communications pattern, (e.g., by sending a byte-based signal to the board, which triggers
a response in a known name-value pair), then you are likely to be ‘off by one’ response.
That is, if you do the following in NetLogo code:
arduino:write-byte b
show arduino:get "varname"
You are likely to get the value ofvarname from the PRIOR command represented by
writing the byte b. This is because the second line of NetLogo code will execute while the
Arduino is off generating a new value for varname .
There are ways of getting around this (simulating a blocking interface by polling on a value
to indicate fresh “news” on varname ). But this extension works best in settings where the
Arduino Sketch is “chatty” and the NetLogo model samples this stream when it needs
data.
Compatibility
This code has been tested on Windows 7 and 10 with 32-bit NetLogo and on Mac OS X.
You are likely to encounter issues when running this with 64-bit NetLogo in Windows 8 or
Windows 10, so if you have Windows 8 or 10, please download the 32-Bit version of
NetLogo if you plan on using the Arduino extension. We strive for cross-platform
compatibility across Mac, Win, and Linux. So if you have troubles, please let us know.
Questions
If you run into problems or have questions about the extension, please emailccl-feedback
or cbrady@inquirelearning.com.
Primitives
arduino:primitives arduino:ports arduino:open arduino:close arduino:get arduino:writestring arduino:write-int arduino:write-byte arduino:is-open?
arduino:primitives
arduino:primitives
Reports a list of primitives available in the extension, with basic hints about their syntax.
arduino:ports
arduino:ports
Reports a list of port names
arduino:open
arduino:open port-name
Opens the port named port-name.
arduino:close
arduino:close
Closes the currently open port.
arduino:get
arduino:get var-name
Reads and reports the value associated with var-name on the Arduino board. Note: varname is case insensitive.
arduino:write-string
arduino:write-string string-message
Writes a string message to the currently open port.
arduino:write-int
arduino:write-int int-message
Writes a integer message to the currently open port.
arduino:write-byte
arduino:write-byte byte-message
Writes a byte message to the currently open port.
arduino:is-open?
arduino:is-open?
Reports a boolean value (true or false) indicating if a port is open.
NetLogo Array Extension
Using
The array extension is pre-installed in NetLogo.
To use the array extension in your model, add a line to the top of your Code tab:
extensions [array]
If your model already uses other extensions, then it already has anextensions line in it, so
just add array to the list.
For more information on using NetLogo extensions, see theExtensions Guide
When to Use
In general, anything you can do with an array in NetLogo, you could also just use a list for.
But you may want to consider using an array instead for speed reasons. Lists and arrays
have different performance characteristics, so you may be able to make your model run
faster by selecting the appropriate data structure.
Arrays are useful when you need a collection of values whose size is fixed. You can
quickly access or alter any item in an array if you know its position.
Unlike NetLogo’s lists and strings, arrays are “mutable”. That means that you can actually
modify them directly, rather than constructing an altered copy as with lists. If the array is
used in more than one place in your code, any changes you make will show up
everywhere. It’s tricky to write code involving mutable structures and it’s easy to make
subtle errors or get surprising results, so we suggest sticking with lists and strings unless
you’re certain you want and need mutability.
Example use of Array Extension
let a array:from-list n-values 5 [0]
print a
=> {{array: 0 0 0 0 0}}
print array:length a
=> 5
foreach n-values 5 [ i -> i ] [ i -> array:set a i i * i ]
print a
=> {{array: 0 1 4 9 16}}
print array:item a 0
=> 0
print array:item a 3
=> 9
array:set a 3 50
print a
=> {{array: 0 1 4 50 16}}
Primitives
array:from-list array:item array:set array:length array:to-list
array:from-list
array:from-list
array:from-list list
Reports a new array containing the same items in the same order as the input list.
array:item
array:item array index
Reports the item in the given array with the given index (ranging from zero to the length of
the array minus one).
array:set
array:set array index value
Sets the item in the given array with the given index (ranging from zero to the length of
the array minus one) to the given value.
Note that unlike the replace-item primitive for lists, a new array is not created. The given
array is actually modified.
array:length
array:length array
Reports the length of the given array, that is, the number of items in the array.
array:to-list
array:to-list array
Reports a new list containing the same items in the same order as the given array.
NetLogo Bitmap Extension
Using
The bitmap extension is pre-installed in NetLogo. For instructions on using it, or for more
information about NetLogo extensions, see the NetLogo User Manual.
What does the Bitmap Extension do?
The Bitmap Extension allows you to manipulate and import images into the drawing and
patches. It offers features not provided by the NetLogo core primitives, such as: scaling,
manipulation of different color channels, and width and height reporters.
Getting started
To import and manipulate images you will need to include the bitmap extension in your
NetLogo model.
extensions[ bitmap ]
The image file formats supported are determined by your Java virtual machine’s imageio
library. Typically this is PNG, JPG, GIF, and BMP. PNG is a good, standard choice that is
likely to work everywhere.
If the image format supports transparency (alpha), that information will be imported as
well.
Primitives
bitmap:average-color bitmap:channel bitmap:copy-to-drawing bitmap:copy-to-pcolors
bitmap:difference-rgb bitmap:export bitmap:from-view bitmap:to-grayscale bitmap:height
bitmap:import bitmap:scaled bitmap:width
bitmap:average-color
bitmap:average-color image
Reports a 3-element list describing the amount of R, G, and B inimage, by summing
across all pixels, and normalizing each component by the number of pixels in the image,
so each component ranges from 0 to 255.
bitmap:channel
bitmap:channel image channel
Extracts either the alpha, red, green, or blue channel from an image. The inputchannel
should be an integer 0-3 indicating the channel to remove (alpha=0, red=1, green=2,
blue=3). The resulting image is a grayscale image representing specified channel.
bitmap:copy-to-drawing
bitmap:copy-to-drawing image x y
Imports the given image into the drawing without scaling the image at the given pixel
coordinates.
bitmap:copy-to-pcolors
bitmap:copy-to-pcolors image boolean
Imports the given image into the pcolors, scaled to fit the world. The second input
indicates whether the colors should be interpreted as NetLogo colors or left as RGB
colors. false means RGB colors.
bitmap:difference-rgb
bitmap:difference-rgb image1 image2
Reports an image that is the absolute value of the pixel-wise RGB difference between two
images. Note that image1 and image2 MUST be the same width and height as each other,
or errors will ensue.
bitmap:export
bitmap:export image filename
Writes image to filename.
bitmap:from-view
bitmap:from-view
Reports an image of the current view.
bitmap:to-grayscale
bitmap:to-grayscale image
Converts the given image to grayscale.
bitmap:height
bitmap:height image
Reports the height of given image
bitmap:import
bitmap:import filename
Reports a LogoBitmap containing the image at filename.
bitmap:scaled
bitmap:scaled image width height
Reports a new image that is image scaled to the given width and height
bitmap:width
bitmap:width image
Reports the width of the given image
NetLogo Cf Extension
Using
The CF extension currently includes primitives that allow you to do things similar toif-else
if -else chains you see in other languages, as well as things similar toswitches in other
languages. However, it does it in a more flexible way than many languages. A few quick
examples to get you started:
let x 5
let y 7
cf:when
cf:case [ x > y ] [ print "x is bigger than y!" ]
cf:case [ x < y ] [ print "x is less than y!" ]
cf:else
[ print "x is the same as y!" ]
let my-awesome-number 5
cf:match my-awesome-number
cf:case [ [n] -> n > 7 ] [ print "The number is greater than 7!" ]
cf:case [ [n] -> n < 3 ] [ print "The number is less than 3!" ]
cf:else
[ print "The number is somewhere in between 3 and 7!" ]
Cases
Central to this extension is the concept of a case. A case is simply a list of two elements,
where the first element is a reporter and the second element is either a reporter or a
command. The first element, called the condition, must report either true or false. The
second argument is called the consequent. If you’re curious about how CF works, keep
reading this section. Otherwise, feel free to skip to the list of primitives; you don’t need to
understand the internals to start using CF.
Almost all primitives in the CF extension take a list of cases as an argument. Typically, they
go through the cases, looking for a true condition. When they find one, they then run the
consequent. Although CF provides primitives that make constructing a list of cases easy,
you could actually just build such a list with primitives already in NetLogo, like so:
let x 5
let y 7
let list-of-cases (list
(list task [ x > y ] task [ print "x is greater than y!" ])
(list task [ x < y ] task [ print "x is less than y!" ])
(list task [ true ] task [ print "x is the same as y!" ])
)
However, this is not very nice looking. With CF, you can write it like this instead:
let x 5
let y 7
let list-of-cases
cf:case [ x > y ] [ print "x is greater than y!" ]
cf:case [ x < y ] [ print "x is less than y!" ]
cf:else
[ print "x is the same as y!" ]
Primitives
cf:when cf:select cf:match cf:matching cf:case cf:case-is cf:else
cf:when
cf:when list-of-cases
Runs the command task from the first case in the list with a true condition. For instance:
let x 3
cf:when
cf:case [ x < 2 ] [ print
cf:case [ x < 4 ] [ print
cf:case [ x < 6 ] [ print
cf:else
[ print
"x
"x
"x
"x
is
is
is
is
less than 2!" ]
less than 4!" ]
less than 6!" ]
greater than or equal to 6!" ]
The above code will print out x is less than 4! since that’s the first case with a true
condition.
If no true case is found, and no cf:else given, cf:when will error with a suggestion for a fix.
cf:select
cf:select list-of-cases
Picks the first case in the list with a true condition and reports the result of its consequent.
The consequents of the cases in a cf:select must be reporter tasks. Thus, cf:select is
exactly like cf:when , except that it reports the value from the true case, rather than just
running it. For example:
let x 3
print cf:select
cf:case [ x < 2 ] [ "x is
cf:case [ x < 4 ] [ "x is
cf:case [ x < 6 ] [ "x is
cf:else
[ "x is
less than 2!" ]
less than 4!" ]
less than 6!" ]
greater than or equal to 6!" ]
The above code will print out x is less than 4! since that’s the first case with a true
condition.
If no true case is found, and no cf:else given, cf:select will error with a suggestion for a
fix.
cf:match
cf:match value list-of-cases
is like cf:when , except that it applies the conditions in its cases to the given value.
For instance:
cf:match
ask patch 0 0 [ set pcolor red ]
cf:match ([ pcolor ] of patch 0 0)
cf:case [ [c] -> c = green ] [ print "The center patch is green!" ]
cf:case [ [c] -> c = red ] [ print "The center patch is red!" ]
cf:case [ [c] -> c = blue ] [ print "The center patch is blue!" ]
cf:else
[ print "I don't know what color the center patch is!" ]
The above code will print out The center patch is green! since that’s the first case with a
true condition.
The value is also passed to the consequent of the case. For instance:
cf:match one-of turtles
cf:case [ [t] -> [color] of t = red ] [ [t] -> ask t [ show "I'm red!" ] ]
cf:case [ [t] -> [color] of t = blue ] [ [t] -> ask t [ show "I'm blue!" ] ]
cf:else
[ [t] -> ask t [ show "I'm some other color!" ] ]
If no matching case is found, cf:match will error with a suggestion for a fix.
cf:matching
value cf:matching list-of-cases
cf:matching
cf:matching
is like cf:match, except that it reports the result of the matching case.
is to cf:match as cf:select is to cf:when . For instance:
let my-awesome-number 3
print my-awesome-number cf:matching
cf:case [ [num] -> num < 2 ] [ "The number
cf:case [ [num] -> num < 4 ] [ "The number
cf:case [ [num] -> num < 6 ] [ "The number
cf:else
[ "The number is greater
is less
is less
is less
than or
than 2!"
than 4!"
than 6!"
equal to
]
]
]
6!" ]
The above code will print out The number is less than 4! since that’s the first case with a
true condition. cf:matching also applies the consequent of the matching case to the given
value, just like cf:match:
print (one-of turtles) cf:matching
cf:case [ [t] -> [color] of t = red ] [ [t] -> [ "I'm red!" ] of t ]
cf:case [ [t] -> [color] of t = blue ] [ [t] -> [ "I'm blue!" ] of t ]
cf:else
[ [t] -> [ "I'm some other color!" ] of t ]
If no matching case is found, cf:matching will error with a suggestion for a fix.
cf:case
cf:case condition consequent list-of-remaining-cases
allows you to construct a list of cases that the other primitives will then pick from. It
constructs a new case from the the two given tasks and adds it to the front of the list of
remaining cases. Thus, you can chain it together with other instances of cf:case to create
an arbitrarily long list of cases.
cf:case
Note that because the condition in a case is just an anonymous reporter, you can check for
many common conditions in a very concise manner. For instance, if we want to do
something depending on the breed of a turtle, you can do:
cf:match my-turtle
cf:case is-wolf? [ show "Growl!" ]
cf:case is-a-sheep? [ show "Baah!" ]
cf:case is-dog? [ show "Bark!" ]
cf:case is-cat? [ show "Meow!" ]
cf:else [ show "I'm not sure what sound to make..." ]
cf:case-is
cf:case-is relationship consequent list-of-remaining-cases
allows you to write some common uses ofcf:case in cf:match or cf:matching
in a more concise, readable way. The given reporter should be a relationship such as =, <,
or member? . cf:case-is then fills in the second argument of the reporter with the given
value. This is much easier to understand in an example:
cf:case-is
let x 5
print x cf:matching
cf:case-is = 0 [ "x is 0!" ]
cf:case-is = 1 [ "x is 1!" ]
cf:case-is > 2 [ "x is greater than 2!" ]
cf:case-is member? [ -1 -2 -3] [ "x is either -1, -2, or -3" ]
cf:else [ "x is something else" ]
Thus, cf:case-is allows you to do something quite similar toswitch in some other
languages, but is also much more flexible.
cf:else
cf:else command/reporter
creates a case where the condition is always true. Thus, it allows you to create a
case that will be run if all the other cases fail. You should almost always finish up a chain of
cases with cf:else . However, if you’d prefer to error rather than have a default case, you
can replace cf:else with [], like so:
cf:else
let x -5
cf:when
cf:case [ 0 < x and x < 10 ] [ print "x is between 0 and 10!" ]
cf:case [ x < 100 ] [ print "x is less than 100!" ]
[]
The above code will error, since no matching case will be found.
NetLogo Csv Extension
Common use cases and examples
Read a file all at once
Just use csv:from-file "/path/to/myfile.csv"! See from-file for more information.
Read a file one line at a time
For really big files, you may not want to store the entire file in memory, but rather just process it a line at a
time. For instance, if you want to sum each of the columns of a numeric CSV file, you can do:
to-report sum-columns [ file ]
file-open file
set result csv:from-row file-read-line
while [ not file-at-end? ] [
let row csv:from-row file-read-line
set result (map [?1 + ?2] result row)
]
file-close
report result
end
You can also use this technique to…
Read a file one line per tick
Here’s an example model that reads in a file one line per tick:
globals [ data ]
to setup
clear-all
file-close-all % Close any files open from last run
file-open "data.csv"
% other setup goes here
reset-ticks
end
to go
if file-at-end? [ stop ]
set data csv:from-row file-read-line
% model update goes here
tick
end
Write a file
Just use csv:to-file "/path/to/myfile.csv" my-data! See to-file for more information.
Primitives
Formatting NetLogo data as CSV
csv:to-row csv:to-string csv:to-file
Parsing CSV input to NetLogo data
csv:from-row csv:from-string csv:from-file
csv:from-row
csv:from-row string
csv:from-row string delimiter
Parses the given string as though it were a row from a CSV file and returns it as a list of values. For example:
observer> show csv:from-row "one,two,three"
observer: ["one" "two" "three"]
Quotes can be used when items contain commas:
observer> show csv:from-row "there's,a,comma,\"in,here\""
observer: ["there's" "a" "comma" "in,here"]
You can put two quotes in a row to put an actual quote in an entry. If the entry is not quoted, you can just use
one quote:
observer> foreach (csv:from-row "he said \"hi there\",\"afterwards, she said \"\"hello\"\"\"") print
he said "hi there"
afterwards, she said "hello"
Number-like-entries will be parsed as numbers:
observer> show csv:from-row "1,-2.5,1e3"
observer: [1 -2.5 1000]
true
and false with any capitalization will be parsed as booleans:
observer> show csv:from-row "true,TRUE,False,falsE"
observer: [true true false false]
To use a different delimiter, you can specify a second, optional argument. Only single character delimiters are
supported:
observer> show (csv:from-row "1;2;3" ";")
observer: [1 2 3]
Different types of values can be mixed freely:
observer> show csv:from-row "one,2,true"
observer: ["one" 2 true]
csv:from-string
csv:from-string string
csv:from-string string delimiter
Parses a string representation of one or more CSV rows and returns it as a list of lists of values. For example:
observer> show csv:from-string "1,two,3\nfour,5,true"
observer: [[1 "two" 3] ["four" 5 true]]
csv:from-file
csv:from-file csv-file
csv:from-file csv-file delimiter
Parses an entire CSV file to a list of lists of values. For example, if we have a fileexample.csv that contains:
1,2,3
4,5,6
7,8,9
10,11,12
Then, we get:
observer> show csv:from-file "example.csv"
observer: [[1 2 3] [4 5 6] [7 8 9] [10 11 12]]
The parser doesn’t care if the rows have different numbers of items on them. The number of items in the rows
list will always be + 1 , though blank lines are skipped. This makes handling files with
headers quite easy. For instance, if we have header.csv that contains:
My Data
2/1/2015
Parameters:
start,stop,resolution,population,birth?
0,4,1,100,true
Data:
time,x,y
0,0,0
1,1,1
2,4,8
3,9,27
This gives:
observer>
observer:
observer:
observer:
observer:
observer:
observer:
observer:
observer:
observer:
observer:
observer:
foreach csv:from-file "header.csv" show
["My Data"]
["2/1/2015"]
["Parameters:"]
["start" "stop" "resolution" "population" "birth?"]
[0 4 1 100 true]
["Data:"]
["time" "x" "y"]
[0 0 0]
[1 1 1]
[2 4 8]
[3 9 27]
csv:to-row
csv:to-row list
csv:to-row list delimiter
Reports the given list as a CSV row. For example:
observer> show csv:to-row ["one" 2 true]
observer: "one,2,true"
csv:to-string
csv:to-string list
csv:to-string list delimiter
Reports the given list of lists as a CSV string. For example:
observer> show csv:to-string [[1 "two" 3] [4 5]]
observer: "1,two,3\n4,5"
csv:to-file
csv:to-file csv-file list
csv:to-file csv-file list delimiter
Writes the given list of lists to a new CSV file. For example:
observer> csv:to-file "myfile.csv" [[1 "two" 3] [4 5]]
will result in a file myfile.csv containing:
1,two,3
4,5
NetLogo Gis Extension
Using
This extension adds GIS (Geographic Information Systems) support to NetLogo. It
provides the ability to load vector GIS data (points, lines, and polygons), and raster GIS
data (grids) into your model.
The extension supports vector data in the form of ESRI shapefiles. The shapefile (.shp)
format is the most common format for storing and exchanging vector GIS data. The
extension supports raster data in the form of ESRI ASCII Grid files. The ASCII grid file
(.asc or .grd) is not as common as the shapefile, but is supported as an interchange
format by most GIS platforms.
How to use
In general, you first define a transformation between GIS data space and NetLogo space,
then load datasets and perform various operations on them. The easiest way to define a
transformation between GIS space and NetLogo space is to take the union of the
“envelopes” or bounding rectangles of all of your datasets in GIS space and map that
directly to the bounds of the NetLogo world. See GIS General Examples for an example of
this technique.
You may also optionally define a projection for the GIS space, in which case datasets will
be re-projected to match that projection as they are loaded, as long as each of your data
files has an associated .prj file that describes the projection or geographic coordinate
system of the data. If no associated .prj file is found, the extension will assume that the
dataset already uses the current projection, regardless of what that projection is.
Once the coordinate system is defined, you can load datasets usinggis:load-dataset. This
primitive reports either a VectorDataset or a RasterDataset, depending on what type of file
you pass it.
A VectorDataset consists of a collection of VectorFeatures, each one of which is a point,
line, or polygon, along with a set of property values. A single VectorDataset may contain
only one of the three possible types of features.
There are several things you can do with a VectorDataset: ask it for the names of the
properties of its features, ask it for its “envelope” (bounding rectangle), ask for a list of all
VectorFeatures in the dataset, search for a single VectorFeature or list of VectorFeatures
whose value for a particular property is less than or greater than a particular value, or lies
within a given range, or matches a given string using wildcard matching ("*", which
matches any number of occurrences of any characters). If the VectorFeatures are
polygons, you can also apply the values of a particular property of the dataset’s features to
a given patch variable.
There are also several things you can do with a VectorFeature from a VectorDataset: ask
it for a list of vertex lists, ask it for a property value by name, ask it for its centroid (center of
gravity), and ask for a subset of a given agentset whose agents intersect the given
VectorFeature. For point data, each vertex list will be a one-element list. For line data,
each vertex list will represent the vertices of a line that makes up that feature. For polygon
data, each vertex list will represent one “ring” of the polygon, and the first and last vertex
of the list will be the same. The vertex lists are made up of values of type Vertex, and the
centroid will be a value of type Vertex as well.
There are a number of operations defined for RasterDatasets as well. Mostly these involve
sampling the values in the dataset, or re-sampling a raster to a different resolution. You
can also apply a raster to a given patch variable, and convolve a raster using an arbitrary
convolution matrix.
Code Example: GIS General Examples has general examples of how to
use the extension
Code Example: GIS Gradient Example is a more advanced example of
raster dataset analysis.
Known Issues
Values of type RasterDataset, VectorDataset, VectorFeature, and Vertex are not handled
properly by export-world and import-world . To save datasets, you must use the
gis:store-dataset primitive.
There is currently no way to distinguish positive-area “shell” polygons from negative-area
“hole” polygons, or to determine which holes are associated with which shells.
Credits
The primary developer of the GIS extension was Eric Russell.
The GIS extension makes use of several open-source software libraries. For copyright and
license information on those, see the copyright section of the manual. The extension also
contains elements borrowed from My World GIS.
This documentation and the example NetLogo models are in the public domain. The GIS
extension itself is free and open source software. See the README.md file in the
extension/gis directory for details.
We would love to hear your suggestions on how to improve the GIS extension, or just
about what you’re using it for. Post questions and comments at the NetLogo Users Group,
or write directly to Eric Russell and the NetLogo team at ccl-gis@ccl.northwestern.edu
Primitives
RasterDataset Primitives
gis:width-of gis:height-of gis:raster-value gis:set-raster-value gis:minimum-of
gis:maximum-of gis:sampling-method-of gis:set-sampling-method gis:raster-sample
gis:raster-world-envelope gis:create-raster gis:resample gis:convolve gis:apply-raster
Dataset Primitives
gis:load-dataset gis:store-dataset gis:type-of gis:patch-dataset gis:turtle-dataset
gis:link-dataset
VectorDataset Primitives
gis:shape-type-of gis:property-names gis:feature-list-of gis:vertex-lists-of
gis:centroid-of gis:location-of gis:property-value gis:find-features gis:find-onefeature gis:find-less-than gis:find-greater-than gis:find-range gis:property-minimum
gis:property-maximum gis:apply-coverage gis:coverage-minimum-threshold gis:setcoverage-minimum-threshold gis:coverage-maximum-threshold gis:set-coverage-maximumthreshold gis:intersects? gis:contains? gis:contained-by? gis:have-relationship?
gis:relationship-of gis:intersecting
Coordinate System Primitives
gis:set-transformation gis:set-transformation-ds gis:set-world-envelope gis:set-worldenvelope-ds gis:world-envelope gis:envelope-of gis:envelope-union-of gis:loadcoordinate-system gis:set-coordinate-system
Drawing Primitives
gis:drawing-color gis:set-drawing-color gis:draw gis:fill gis:paint gis:import-wmsdrawing
gis:set-transformation
gis:set-transformation gis-envelope netlogo-envelope
Defines a mapping between GIS coordinates and NetLogo coordinates. Thegis-envelope
and netlogo-envelope parameters must each be four-element lists consisting of:
[minimum-x maximum-x minimum-y maximum-y]
The scale of the transformation will be equal to the minimum of the scale necessary to
make the mapping between the ranges of x values and the scale necessary to make the
mapping between the ranges of y values. The GIS space will be centered in NetLogo
space.
For example, the following two lists would map all of geographic (latitude and longitude)
space in degrees to NetLogo world space, regardless of the current dimensions of the
NetLogo world:
(list -180 180 -90 90)
(list min-pxcor max-pxcor min-pycor max-pycor)
However, if you’re setting the envelope of the NetLogo world, you should probably be
using set-world-envelope.
gis:set-transformation-ds
gis:set-transformation-ds gis-envelope netlogo-envelope
Does the same thing as set-transformation above, except that it allows the scale for
mapping the range of x values to be different than the scale for y values. The “-ds” on the
end stands for “different scales”. Using different scales will cause distortion of the shape
of GIS features, and so it is generally not recommended, but it may be useful for some
models.
Here is an example of the difference betweenset-transformation and set-transformationds:
Using [set-transformation]
(#gisset-transformation), the
scale along the x and y axis is
the same, preserving the round
shape of the Earth in this
Orthographic projection.
Using [set-transformation-ds](#gissettransformation-ds), the scale along
the x axis is stretched so that the
earth covers the entire NetLogo View,
which in this case distorts the shape
of the Earth.
gis:set-world-envelope
gis:set-world-envelope gis-envelope
A shorthand for setting the transformation by mapping the envelope of the NetLogo world
to the given envelope in GIS space, while keeping the scales along the x and y axis the
same. It is equivalent to:
set-transformation gis-envelope (list min-pxcor max-pxcor min-pycor max-pycor)
This primitive is supplied because most of the time you’ll want to set the envelope of the
entire NetLogo world, rather than just a part of it.
gis:set-world-envelope-ds
gis:set-world-envelope-ds gis-envelope
A shorthand for setting the transformation by mapping the envelope of the NetLogo world
to the given envelope in GIS space, using different scales along the x and y axis if
necessary. It is equivalent to:
set-transformation-ds gis-envelope (list min-pxcor max-pxcor min-pycor max-pycor)
See the pictures above for the difference between using equal scales for x and y
coordinates and using different scales.
gis:world-envelope
gis:world-envelope
Reports the envelope (bounding rectangle) of the NetLogo world, transformed into GIS
space. An envelope consists of a four-element list of the form:
[minimum-x maximum-x minimum-y maximum-y]
gis:envelope-of
gis:envelope-of thing
Reports the envelope (bounding rectangle) of thing in GIS coordinates. The thing may be
an Agent, an AgentSet, a RasterDataset, a VectorDataset, or a VectorFeature. An
envelope consists of a four-element list of the form:
[minimum-x maximum-x minimum-y maximum-y]
gis:envelope-union-of
gis:envelope-union-of envelope1 envelope2
gis:envelope-union-of envelope1 ...
Reports an envelope (bounding rectangle) that entirely contains the given envelopes. An
envelope consists of a four-element list of the form
[minimum-x maximum-x minimum-y maximum-y]
No assumption is made about the coordinate system of the arguments, though if they are
not in the same coordinate system, results will be unpredictable.
gis:load-coordinate-system
gis:load-coordinate-system file
Loads a new global projection used for projecting or re- projecting GIS data as it is loaded
from a file. The file must contain a valid Well-Known Text (WKT) projection description.
WKT projection files are frequently distributed alongside GIS data files, and usually have a
“.prj” filename extension.
Relative paths are resolved relative to the location of the current model, or the user’s
home directory if the current model hasn’t been saved yet.
The GIS extension does not support all WKT coordinate systems and projections. Only
geographic ("GEOGCS") and projected ("PROJCS") coordinate systems are supported. For
projected coordinate systems, only the following projections are supported:
Albers_Conic_Equal_Area
Lambert_Conformal_Conic_2SP
Polyconic
Lambert_Azimuthal_Equal_Area
Mercator_1SP
Robinson
Azimuthal_Equidistant
Miller
Stereographic
Cylindrical_Equal_Area
Oblique_Mercator
Transverse_Mercator
Equidistant_Conic
hotine_oblique_mercator
Gnomonic
Orthographic
See remotesensing.org for a complete list of WKT projections and their parameters.
gis:set-coordinate-system
gis:set-coordinate-system system
Sets the global projection used for projecting or re- projecting GIS data as it is loaded. The
system must be either a string in Well-Known Text (WKT) format, or a NetLogo list that
consists of WKT converted to a list by moving each keyword inside its associated brackets
and putting quotes around it. The latter is preferred because it makes the code much more
readable.
The same limitations on WKT support apply as described above in the documentation for
load-coordinate-system
gis:load-dataset
gis:load-dataset file
Loads the given data file, re-projecting the data as necessary if a global projection is
defined and if the data file itself has an associated .prj file, then reports the resulting
dataset.
If no “.prj” file is present, then load-dataset assumes that the projection of the data being
loaded is the same as the current global coordinate system.
Relative paths are resolved relative to the location of the current model, or the user’s
home directory if the current model hasn’t been saved yet.
Currently, two types of data file are supported:
“.shp” (ESRI shapefile): contains vector data, consisting of points, lines, or polygons.
When the target file is a shapefile, load-dataset reports a VectorDataset.
“.asc” or “.grd” (ESRI ASCII grid): contains raster data, consisting of a grid of values.
When the target file is an ASCII grid file, load-dataset reports a RasterDataset.
gis:store-dataset
gis:store-dataset dataset file
Saves the given dataset to the given file. If the name of the file does not have the proper
file extension, the extension will be automatically appended to the name. Relative paths
are resolved relative to the location of the current model, or the user’s home directory if
the current model hasn’t been saved yet.
Currently, this primitive only works for RasterDatasets, and it can only save those datasets
as ESRI ASCII grid files.
gis:type-of
gis:type-of dataset
Reports the type of the given GIS dataset: either “VECTOR” or “RASTER”
gis:patch-dataset
gis:patch-dataset patch-variable
Reports a new raster whose cells correspond directly to NetLogo patches, and whose cell
values consist of the values of the given patch variable. This primitive is basically the
inverse of apply-raster; apply-raster copies values from a raster dataset to a patch
variable, while this primitive copies values from a patch variable to a raster dataset.
gis:turtle-dataset
gis:turtle-dataset turtle-set
Reports a new, point VectorDataset built from the turtles in the given agentset. The points
are located at locations of the turtles, translated from NetLogo space into GIS space using
the current coordinate transformation. And the dataset’s properties consist of all of the
turtle variables common to every turtle in the agentset.
gis:link-dataset
gis:link-dataset link-set
Reports a new, line VectorDataset built from the links in the given agentset. The endpoints
of each line are at the location of the turtles connected by each link, translated from
NetLogo space into GIS space using the current coordinate transformation. And the
dataset’s properties consist of all of the link variables common to every link in the
agentset.
gis:shape-type-of
gis:shape-type-of VectorDataset
Reports the shape type of the given dataset. The possible output values are “POINT”,
“LINE”, and “POLYGON”.
gis:property-names
gis:property-names VectorDataset
Reports a list of strings where each string is the name of a property possessed by each
VectorFeature in the given VectorDataset, suitable for use in gis:property-value.
gis:feature-list-of
gis:feature-list-of VectorDataset
Reports a list of all VectorFeatures in the given dataset.
gis:vertex-lists-of
gis:vertex-lists-of VectorFeature
Reports a list of lists of Vertex values. For point datasets, each vertex list will contain
exactly one vertex: the location of a point. For line datasets, each vertex list will contain at
least two points, and will represent a “polyline”, connecting each adjacent pair of vertices
in the list. For polygon datasets, each vertex list will contain at least three points,
representing a polygon connecting each vertex, and the first and last vertices in the list will
be the same.
gis:centroid-of
gis:centroid-of VectorFeature
Reports a single Vertex representing the centroid (center of gravity) of the given feature.
For point datasets, the centroid is defined as the average location of all points in the
feature. For line datasets, the centroid is defined as the average of the locations of the
midpoints of all line segments in the feature, weighted by segment length. For polygon
datasets, the centroid is defined as the weighted sum of the centroids of a decomposition
of the area into (possibly overlapping) triangles. See this FAQ for more details on the
polygon centroid algorithm.
gis:location-of
gis:location-of Vertex
Reports a two-element list containing the x and y values (in that order) of the given vertex
translated into NetLogo world space using the current transformation, or an empty list if
the given vertex lies outside the NetLogo world.
gis:property-value
gis:property-value VectorFeature property-name
Reports the value of the property with the given name for the given VectorDataset. The
reported value may be a number, a string, or a boolean value, depending on the type of
the field in the underlying data file.
For shapefiles, values from dBase CHARACTER and DATE fields are returned as strings,
values from NUMBER and FLOAT fields are returned as numbers, and values from LOGICAL
fields are returned as boolean values. MEMO fields are not supported. DATE values are
converted to strings using ISO 8601 format (YYYY-MM-DD).
gis:find-features
gis:find-features VectorDataset property-name specified-value
Reports a list of all VectorFeatures in the given dataset whose value for the property
property-name matches specified-value (a string). Value comparison is not case sensitive,
and the wildcard character "*" will match any number of occurrences (including zero) of
any character.
gis:find-one-feature
gis:find-one-feature VectorDataset property-name specified-value
Reports the first VectorFeature in the dataset whose value for the propertyproperty-name
matches the given string. Value comparison is not case sensitive, and the wildcard
character "*" will match any number of occurrences (including zero) of any character.
Features are searched in the order that they appear in the data file that was the source of
the dataset, and searching stops as soon as a match is found. Reports nobody if no
matching VectorFeature is found.
gis:find-less-than
gis:find-less-than VectorDataset property-name value
Reports a list of all VectorFeatures in the given dataset whose value for the property
property-name is less than the given value. String values are compared using casesensitive lexicographic order as defined in the Java Documentation. Using a string value
for a numeric property or a numeric value for a string property will cause an error.
gis:find-greater-than
gis:find-greater-than VectorDataset property-name value
Reports a list of all VectorFeatures in the given dataset whose value for the property
property-name is greater than the given value. String values are compared using casesensitive lexicographic order as defined in the Java Documentation. Using a string value
for a numeric property or a numeric value for a string property will cause an error.
gis:find-range
gis:find-range VectorDataset property-name minimum-value maximum-value
Reports a list of all VectorFeatures in the given dataset whose value for the property
property-name is strictly greater than minimum-value and strictly less than maximumvalue. String values are compared using case-sensitive lexicographic order as defined in
the Java Documentation. Using a string value for a numeric property or a numeric value for
a string property will cause an error.
gis:property-minimum
gis:property-minimum VectorDataset property-name
Reports the smallest value for the given property over all of the VectorFeatures in the
given dataset. String values are compared using case-sensitive lexicographic order as
defined in the Java Documentation.
gis:property-maximum
gis:property-maximum VectorDataset property-name
Reports the largest value for the given property over all of the VectorFeatures in the given
dataset. String values are compared using case-sensitive lexicographic order as defined
in the Java Documentation.
gis:apply-coverage
gis:apply-coverage VectorDataset property-name patch-variable
Copies values from the given property of the VectorDataset’s features to the given patch
variable. The dataset must be a polygon dataset; points and lines are not supported.
For each patch, it finds all VectorFeatures that intersect that patch. Then, if the property is
a string property, it computes the majority value by computing the total area of the patch
covered by VectorFeatures having each possible value of the property, then returning the
value which represents the largest proportion of the patch area. If the property is a
numeric property, it computes a weighted average of property values from all
VectorFeatures which intersect the patch, weighted by the proportion of the patch area
they cover.
There are two exceptions to this default behavior:
If a percentage of a patches’ area greater than the coverage-maximum-threshold is
covered by a single VectorFeature, then the property value from that VectorFeature
is copied directly. If more than one VectorFeature covers a percentage of area
greater than the threshold, only the first will be used.
If the total percentage of a patches’ area covered by VectorFeatures is less than the
coverage-minimum-threshold, the target patch variable is set to Not A Number.
By default, the minimum threshold is 10% and the maximum threshold is 33%. These
values may be modified using the four primitives that follow.
gis:coverage-minimum-threshold
gis:coverage-minimum-threshold
Reports the current coverage minimum threshold used by gis:apply-coverage.
gis:set-coverage-minimum-threshold
gis:set-coverage-minimum-threshold new-threshold
Sets the current coverage minimum threshold to be used by gis:apply-coverage.
gis:coverage-maximum-threshold
gis:coverage-maximum-threshold
Reports the current coverage maximum threshold used by gis:apply-coverage.
gis:set-coverage-maximum-threshold
gis:set-coverage-maximum-threshold new-threshold
Sets the current coverage maximum threshold to be used by gis:apply-coverage.
gis:intersects?
gis:intersects? x y
Reports true if the given objects’ spatial representations share at least one point in
common, and false otherwise. The objects x and y may be any one of:
a VectorDataset, in which case the object’s spatial representation is the union of all the
points, lines, or polygons the dataset contains.
a VectorFeature, in which case the object’s spatial representation is defined by the
point, line, or polygon the feature contains.
A turtle, in which case the spatial representation is a point.
A link, whose spatial representation is a line segment connecting the two points
represented by the turtles the link is connecting.
A patch, whose spatial representation is a rectangular polygon.
An agentset, whose spatial representation is the union of the representations of all of
the agents it contains.
A list containing of any of the items listed here, including another list. The spatial
representation of such a list is the union of the spatial representations of its contents.
gis:contains?
gis:contains? x y
Reports true if every point of y’s spatial representation is also a part of x’s spatial
representation. Note that this means that polygons do contain their boundaries. The
objects x and y may be any one of
a VectorDataset, in which case the object’s spatial representation is the union of all the
points, lines, or polygons the dataset contains.
a VectorFeature, in which case the object’s spatial representation is defined by the
point, line, or polygon the feature contains.
A turtle, in which case the spatial representation is a point.
A link, whose spatial representation is a line segment connecting the two points
represented by the turtles the link is connecting.
A patch, whose spatial representation is a rectangular polygon.
An agentset, whose spatial representation is the union of the representations of all of
the agents it contains.
A list containing of any of the items listed here, including another list. The spatial
representation of such a list is the union of the spatial representations of its contents.
gis:contained-by?
gis:contained-by? x y
Reports true if every point of x’s spatial representation is also a part of y’s spatial
representation. The objects x and y may be any one of:
a VectorDataset, in which case the object’s spatial representation is the union of all the
points, lines, or polygons the dataset contains.
a VectorFeature, in which case the object’s spatial representation is defined by the
point, line, or polygon the feature contains.
A turtle, in which case the spatial representation is a point.
A link, whose spatial representation is a line segment connecting the two points
represented by the turtles the link is connecting.
A patch, whose spatial representation is a rectangular polygon.
An agentset, whose spatial representation is the union of the representations of all of
the agents it contains.
A list containing of any of the items listed here, including another list. The spatial
representation of such a list is the union of the spatial representations of its contents.
gis:have-relationship?
gis:have-relationship? x y
Reports true if the spatial representations of the two objects have the given spatial
relationship, and false otherwise. The spatial relationship is specified using a
Dimensionally Extended Nine- Intersection Model (DE-9IM) matrix. The matrix consists
of 9 elements, each of which specifies the required relationship between the two objects’
interior space, boundary space, or exterior space. The elements must have one of six
possible values:
“T”, meaning the spaces must intersect in some way
“F”, meaning the spaces must not intersect in any way
“0”, meaning the dimension of the spaces’ intersection must be zero (i.e., it must be a
point or non-empty set of points).
“1”, meaning the dimension of the spaces’ intersection must be one (i.e., it must be a
line or non-empty set of line segments).
“2”, meaning the dimension of the spaces’ intersection must be two (i.e., it must be a
polygon or set of polygons whose area is greater than zero).
"*", meaning that the two spaces may have any relationship.
For example, this matrix:
Interior
y Boundary
Exterior
Interior
x
Boundary
Exterior
T
*
F
*
*
F
*
*
*
would return true if and only if some part of object x’s interior lies inside object y’s interior,
and no part of object x’s interior or boundary intersects object y’s exterior. This is
essentially a more restrictive form of the contains? primitive; one in which polygons are
not considered to contain their boundaries.
The matrix is given to the have-relationship? primitive as a string, whose elements are
given in the following order:
1
4
2
5
3
6
7
8
9
So to use the example matrix above, you would write:
gis:have-relationship? x y "T*****FF*"
A much more detailed and formal description of the DE-9IM matrix and the associated
point-set theory can be found in the OpenGIS Simple Features Specification for SQL.
The objects x and y may be any one of:
a VectorDataset, in which case the object’s spatial representation is the union of all the
points, lines, or polygons the dataset contains.
a VectorFeature, in which case the object’s spatial representation is defined by the
point, line, or polygon the feature contains.
A turtle, in which case the spatial representation is a point.
A link, whose spatial representation is a line segment connecting the two points
represented by the turtles the link is connecting.
A patch, whose spatial representation is a rectangular polygon.
An agentset, whose spatial representation is the union of the representations of all of
the agents it contains.
A list containing of any of the items listed here, including another list. The spatial
representation of such a list is the union of the spatial representations of its contents.
gis:relationship-of
gis:relationship-of x y
Reports the Dimensionally Extended Nine-Intersection Model (DE-9IM) matrix that
describes the spatial relationship of the two objects. The matrix consists of 9 elements,
each of which describes the relationship between the two objects’ interior space, boundary
space, or exterior space. Each element will describe the dimension of the intersection of
two spaces, meaning that it may have one of four possible values:
“-1”, meaning the spaces do not intersect
“0”, meaning the dimension of the spaces’ intersection is zero (i.e., they intersect at a
point or set of points).
“1”, meaning the dimension of the spaces’ intersection is one (i.e., they intersect along
one or more lines).
“2”, meaning the dimension of the spaces’ intersection is two (i.e., their intersection is a
non-empty polygon).
For example, the two polygons x and y shown here:
have the following DE-9IM matrix:
Interior
y Boundary
Exterior
Interior
x
Boundary
Exterior
2
1
1
0
2
1
2
1
2
Which would be reported by the relationship-of primitive as the string “212101212”.
A much more detailed and formal description of the DE-9IM matrix and the associated
point-set theory can be found in the OpenGIS Simple Features Specification for SQL.
The objects x and y may be any one of:
a VectorDataset, in which case the object’s spatial representation is the union of all the
points, lines, or polygons the dataset contains.
a VectorFeature, in which case the object’s spatial representation is defined by the
point, line, or polygon the feature contains.
A turtle, in which case the spatial representation is a point.
A link, whose spatial representation is a line segment connecting the two points
represented by the turtles the link is connecting.
A patch, whose spatial representation is a rectangular polygon.
An agentset, whose spatial representation is the union of the representations of all of
the agents it contains.
A list containing of any of the items listed here, including another list. The spatial
representation of such a list is the union of the spatial representations of its contents.
gis:intersecting
patch-set gis:intersecting data
Reports a new agent set containing only those members of the given agent set which
intersect given GIS data, which may be any one of: a VectorDataset, a VectorFeature, an
Agent, an Agent Set, or a list containing any of the above.
gis:width-of
gis:width-of RasterDataset
Reports the number of columns in the dataset. Note that this is the number of cells from
left to right, not the width of the dataset in GIS space.
gis:height-of
gis:height-of RasterDataset
Reports the number of rows in the dataset. Note that this is the number of cells from top to
bottom, not the height of the dataset in GIS space.
gis:raster-value
gis:raster-value RasterDataset x y
Reports the value of the given raster dataset in the given cell. Cell coordinates are
numbered from left to right, and from top to bottom, beginning with zero. So the upper left
cell is (0, 0), and the bottom right cell is (gis:width-of dataset - 1, gis:height-of dataset
- 1).
gis:set-raster-value
gis:set-raster-value RasterDataset x y value
Sets the value of the given raster dataset at the given cell to a new value. Cell coordinates
are numbered from left to right, and from top to bottom, beginning with zero. So the upper
left cell is (0, 0), and the bottom right cell is (gis:width-of dataset - 1, gis:height-of
dataset - 1).
gis:minimum-of
gis:minimum-of RasterDataset
Reports the highest value in the given raster dataset.
gis:maximum-of
gis:maximum-of RasterDataset
Reports the lowest value in the given raster dataset.
gis:sampling-method-of
gis:sampling-method-of RasterDataset
Reports the sampling method used to compute the value of the given raster dataset at a
single point, or over an area smaller than a single raster cell. Sampling is performed by the
GIS extension primitives raster-sample, resample, convolve, and apply-raster. The
sampling method will be one of the following:
"NEAREST_NEIGHBOR": the value of the cell nearest the sampling location is used.
"BILINEAR": the value of the four nearest cells are sampled by linear weighting,
according to their proximity to the sampling site.
"BICUBIC": the value of the sixteen nearest cells are sampled, and their values are
combined by weight according to a piecewise cubic polynomial recommended by
Rifman (see Digital Image Warping, George Wolberg, 1990, pp 129-131, IEEE
Computer Society Press).
"BICUBIC_2": the value is sampled using the same procedure and the same polynomial
as with BICUBIC above, but using a different coefficient. This method may produce
somewhat sharper results than BICUBIC , but that result is data dependent.
For more information on these sampling methods and on raster sampling in general, see
this wikipedia article.
gis:set-sampling-method
gis:set-sampling-method RasterDataset sampling-method
Sets the sampling method used by the given raster dataset at a single point, or over an
area smaller than a single raster cell. Sampling is performed by the GIS extension
primitives raster-sample, resample, convolve, and apply-raster. The sampling method must
be one of the following:
"NEAREST_NEIGHBOR"
"BILINEAR"
"BICUBIC"
"BICUBIC_2"
See sampling-method-of above for a more specific description of each sampling method.
gis:raster-sample
gis:raster-sample RasterDataset sample-location
Reports the value of the given raster over the given location. The location may be any of
the following:
A list of length 2, which is taken to represent a point in netlogo space ([xcor ycor]) of
the sort reported by location-of Vertex. The raster dataset is sampled at the point of that
location.
A list of length 4, which is taken to represent an envelope in GIS space, of the sort
reported by envelope-of. The raster dataset is sampled over the area of that envelope.
A patch, in which case the raster dataset is sampled over the area of the patch.
A turtle, in which case the raster dataset is sampled at the location of that turtle.
A Vertex, in which case the raster dataset is sampled at the location of that Vertex.
If the requested location is outside the area covered by the raster dataset, this primitive
reports the special value representing “not a number”, which is printed by NetLogo as
“NaN”. Using the special “not a number” value as an argument to primitives that expect a
number may cause an error, but you can test the value reported by this primitive to filter
out “not a number” values. A value that is not a number will be neither less than nor
greater than a number value, so you can detect “not a number” values using the following:
let value gis:raster-sample dataset turtle 0
; set color to blue if value is a number, red if value is "not a number"
ifelse (value <= 0) or (value >= 0)
[ set color blue ]
[ set color red ]
If the requested location is a point, the sample is always computed using the method set
by set-sampling-method. If the requested location is an area (i.e., an envelope or patch),
the sample is computed by taking the average of all raster cells covered by the requested
area.
gis:raster-world-envelope
gis:raster-world-envelope RasterDataset x y
Reports the GIS envelope needed to match the boundaries of NetLogo patches with the
boundaries of cells in the given raster dataset. This envelope could then be used as an
argument to set-transformation-ds.
There may be more cells in the dataset than there are patches in the NetLogo world. In
that case, you will need to select a subset of cells in the dataset by specifying which cell in
the dataset you want to match with the upper-left corner of the NetLogo world. Cells are
numbered from left to right, and from top to bottom, beginning with zero. So the upper left
cell is (0, 0), and the bottom right cell is (gis:width-of dataset - 1, gis:height-of dataset
- 1).
gis:create-raster
gis:create-raster width height envelope
Creates and reports a new, empty raster dataset with the given number of columns and
rows, covering the given envelope.
gis:resample
gis:resample RasterDataset envelope width height
Reports a new dataset that consists of the given RasterDataset resampled to cover the
given envelope and to contain the given number of columns and rows. If the new raster’s
cells are smaller than the existing raster’s cells, they will be resampled using the method
set by set-sampling-method. If the new cells are larger than the original cells, they will be
sampled using the "NEAREST_NEIGHBOR" method.
gis:convolve
gis:convolve RasterDataset kernel-rows kernel-columns kernel key-column key-row
Reports a new raster whose data consists of the given raster convolved with the given
kernel.
A convolution is a mathematical operation that computes each output cell by multiplying
elements of a kernel with the cell values surrounding a particular source cell. A kernel is a
matrix of values, with one particular value defined as the “key element”, the value that is
centered over the source cell corresponding to the destination cell whose value is being
computed.
The values of the kernel matrix are given as a list, which enumerates the elements of the
matrix from left to right, top to bottom. So the elements of a 3-by-3 matrix would be listed
in the following order:
1
2
3
4
7
5
8
6
9
The key element is specified by column and row within the matrix. Columns are numbered
from left to right, beginning with zero. Rows are numbered from top to bottom, also
beginning with zero. So, for example, the kernel for the horizontal Sobel operator, which
looks like this:
1
2
1
0
0
(key)
0
-1
-2
-1
would be specified as follows:
let horizontal-gradient gis:convolve dataset 3 3 [1 0 -1 2 0 -2 1 0 -1] 1 1
gis:apply-raster
gis:apply-raster RasterDataset patch-variable
Copies values from the given raster dataset to the given patch variable, resampling the
raster as necessary so that its cell boundaries match up with NetLogo patch boundaries.
This resampling is done as if using resample rather than raster-sample, for the sake of
efficiency. However, patches not covered by the raster are assigned values of “not a
number” in the same way that raster-sample reports values for locations outside the
raster.
gis:drawing-color
gis:drawing-color
Reports the color used by the GIS extension to draw vector features into the NetLogo
drawing layer. Color can be represented either as a NetLogo color (a single number
between zero and 140) or an RGB color (a list of 3 numbers). See details in the Colors
section of the Programming Guide.
gis:set-drawing-color
gis:set-drawing-color color
Sets the color used by the GIS extension to draw vector features into the NetLogo drawing
layer. Color can be represented either as a NetLogo color (a single number between zero
and 140) or an RGB color (a list of 3 numbers). See details in the Colors section of the
Programming Guide.
gis:draw
gis:draw vector-data line-thickness
Draws the given vector data to the NetLogo drawing layer, using the current GIS drawing
color, with the given line thickness. The data may consist either of an entire
VectorDataset, or a single VectorFeature. This primitive draws only the boundary of
polygon data, and for point data, it fills a circle with a radius equal to the line thickness.
gis:fill
gis:fill vector-data line-thickness
Fills the given vector data in the NetLogo drawing layer using the current GIS drawing
color, using the given line thickness around the edges. The data may consist either of an
entire VectorDataset, or a single VectorFeature. For point data, it fills a circle with a radius
equal to the line thickness.
gis:paint
gis:paint RasterDataset transparency
Paints the given raster data to the NetLogo drawing layer. The highest value in the
dataset is painted white, the lowest is painted in black, and the other values are painted in
shades of gray scaled linearly between white and black.
The transparency input determines how transparent the new image in the drawing will be.
Valid inputs range from 0 (completely opaque) to 255 (completely transparent).
gis:import-wms-drawing
gis:import-wms-drawing server-url spatial-reference layers transparency
Imports an image into the NetLogo drawing layer using theWeb Mapping Service protocol,
as defined by the Open Geospatial Consortium.
The spatial reference and layers inputs should be given as strings. The spatial reference
input corresponds to the SRS parameter to the GetMap request as defined in section
7.2.3.5 of version 1.1.1 of the WMS standard. The layers input corresponds to the
LAYERS parameter to the as defined in 7.2.3.3 of version 1.1.1 of the WMS standard.
You can find the list of valid spatial reference codes and layer names by examining the
response to a GetCapabilities request to the WMS server. Consult the relevant standard
for instructions on how to issue a GetCapabilities request to the server and how to
interpret the results.
The transparency input determines how transparent the new image in the drawing will be.
Valid inputs range from 0 (completely opaque) to 255 (completely transparent).
NetLogo Gogo Extension
Usage
The GoGo Extension comes preinstalled when you download and install NetLogo. To use
the extension in your model, add this line to the top of your Code tab:
extensions [ gogo ]
If your model already uses other extensions, then it already has an extensions line in it, so
just add gogo to the list.
After loading the extension, you can see whether one or more HID-based gogos are on
and attached to the computer by typing the following into the command center:
gogo:howmany-gogos
Changes
Compared to previous versions of the GoGo extension, this version offers:
Improved robustness. With prior versions of the GoGo extension, crashes were fairly
common due to problems in the USB-Serial stack across platforms. The switch to HID
improved robustness, and the new extension also uses a “daemon” architecture which
shields NetLogo from any problems that may occur in direct communication with the
GoGo board. The result is a substantial reduction in the number of crashes of NetLogo.
No Installation of Drivers. Because the new GoGo firmware presents the board as an
HID device, the extension could be written so as not to require installing drivers. This
means there is no need for the user to have administrator rights on the computer.
Directionality for Motors. The board now has polarity-ensuring output connectors, so
that “counterclockwise” or “clockwise” can now be specified in code.
Primitives
Other Outputs
gogo:led gogo:beep
Utilities
gogo:read-all
General
gogo:primitives gogo:howmany-gogos
Sensors
gogo:read-sensors gogo:read-sensor
Outputs and Servos
gogo:talk-to-output-ports gogo:set-output-port-power gogo:output-port-on gogo:outputport-off gogo:output-port-clockwise gogo:output-port-counterclockwise gogo:set-servo
gogo:primitives
gogo:primitives
Returns a list of the primitives of this extension.
gogo:howmany-gogos
gogo:howmany-gogos
Reports the number of USB HID devices visible to the computer and having the correct
vendor and product ID to be a GoGo board. A board will only be detected if it is both
connected and powered on. Using this primitive is one way to determine quickly whether a
GoGo board has the HID firmware loaded. (A USB-Serial version of the board will not be
detected.).
gogo:talk-to-output-ports
gogo:talk-to-output-ports list-of-portnames
Establishes a list of output ports that will be controlled with subsequent output-port
commands. See below…
gogo:set-output-port-power
gogo:set-output-port-power power-level
is a number between 0 and 100, reflecting the percentage of maximum
power. Sets the amount of power that will be fed to the output ports indicated in talk-tooutput-ports . This will not affect the on-off state of the output ports. So, for example, if a
motor is already connected to an output port and running, changing its power will change
its speed. If the motor is not running, changing the power level will not turn it on; instead, it
will affect the speed at which the motor starts when it is turned on with output-port-on .
power-level
gogo:output-port-on
gogo:output-port-on
Turns on the output ports which have been indicated with talk-to-output-ports. If none have
been set with talk-to-output-ports, no ports will be turned on.
gogo:output-port-off
gogo:output-port-off
Turns off the output ports which have been indicated with talk-to-output-ports. If none have
been set with talk-to-output-ports, no ports will be turned off.
gogo:output-port-clockwise
gogo:output-port-clockwise
Sets the polarity of the output port(s) that have been specified with talk-to-output-ports, so
that a motor attached to one of these ports would turn clockwise.
gogo:output-port-counterclockwise
gogo:output-port-counterclockwise
Sets the polarity of the output port(s) that have been specified withtalk-to-output-ports,
so that a motor attached to one of these ports would turn counterclockwise.
gogo:set-servo
gogo:set-servo number
Sets the Pulse-Width Modulation (PWM) proportion of the output port(s) that have been
specified with talk-to-output-ports. Note that the servo connectors are the male pins next
to the standard motor connectors. Different servos respond to different PWM ranges, but
all servos read PWM proportions and set the position of their main gear accordingly.
gogo:led
gogo:led on-or-off
Turns the user-LED on or off, depending on the argument. gogo:led 1 turns the LED on;
gogo:led 0 turns it off.
gogo:beep
gogo:beep
Causes the GoGo board to beep.
gogo:read-sensors
gogo:read-sensors
Reports a list containing the current readings of all eight sensors ports of the GoGo.
gogo:read-sensor
gogo:read-sensor which-sensor
Reports the value of sensor number which-sensor, where which-sensor is a number
between 0-7.
gogo:read-all
gogo:read-all
Reports all data available from the board, in a raw-list form useful for debugging.
gogo:send-bytes
gogo:send-bytes list
Sends a list of bytes to the GoGo board. Useful for debugging or for testing any new or
future functionality that is added to the GoGo board with new firmware updates.
NetLogo Ls Extension
LevelSpace fundamentals
LevelSpace must be loaded in a model using extensions [ls] at the top of your model.
Once this is done, a model will be able to load up other models using the LevelSpace
primitives, run commands and reporters in them, and close them down when they are no
longer needed.
Asking and reporting in LevelSpace is conceptually pretty straight forward: You pass blocks
of code to child models, and the child models respond as if you had typed that code into
their Command Center. LevelSpace allows you to report strings, numbers, and lists from a
child to its parent. It is not possible to directly report turtles, patches, links, or any of their
respective sets. Further, it is not possible to push data from a child to its parent - parents
must ask their children to report. This mimicks the way in which turtles cannot “push” data
to the observer, but rely on the observer to ask them for it.
In general, the LevelSpace syntax has been designed to align with existing NetLogo
primitives whenever possible.
Headless and Interactive Models
LevelSpace has two different child model types; headless models and interactive models.
They each have their strengths and weaknesses:
Interactive models * are full-fledged models that give full access to their interface and
widgets, * run a bit slower, and use more memory * are visible by default
Headless Models * only give you access to their view and command center * are faster and
use less memory than interactive models. * are hidden by default
Typically you will want to use headless models when you are running a large number of
models, or if you simply want to run them faster. Interactive models are good if you run a
small amount of models, if you are writing a LevelSpace model and need to be able to
debug, or if you need access to widgets during runtime.
Keeping Track of Models
Child models are kept track of in the extension with an id number, starting with 0, and all
communication from parent to child is done by referencing this number, henceforth referred
to as model-id .
The easiest way to work with multiple models is to store theirmodel-id in a list, and use
NetLogo’s list primitives to sort, filter, etc. them during runtime.
Keeping track of models is important: Most LevelSpace primitives will fail and cause a
runtime interruption if provided a model-id to a non-existing model. You can use ls:modelexists? model-id to check if model-id refers to an existing model.
A general use case: Asking and Reporting
This use case is based on the Model Visualizer and Plotter Example-model from the
NetLogo Models Library.
A simple thing we can do is to open up some models, run them concurrently, and calculate
the average of some reporter. Let’s say that we are interested in finding the mean number
of sheep in a bunch of Wolf Sheep Predation models. First we would open up some of
these models, and set them up:
to setup
ls:reset
ca
ls:create-models 30 "Wolf Sheep Predation.nlogo"
ls:ask ls:models [ set grass? true setup ]
reset-ticks
end
We then want to run all our child models, and then find out what the mean number of
sheep is:
to go
ls:ask ls:models [ go ]
show mean [ count sheep ] ls:of ls:models
end
A general use case: Inter-Model Interactions
This use case is based on the Model Interactions Example-model from the NetLogo Models
Library.
Let’s imagine that we have two models: a Wolf Sheep Predation-model called WSP, and a
Climate Change model called CC. Now let’s imagine that we want the regrowth time in the
wSP model to depend on the temperature in the CC model. Using LevelSpace’s primitives,
we could do something like this:
; save new regrowth time in a temporary LevelSpace let-variable
ls:let new-regrowth-time 25 + ( abs [ temperature - 55 ] ls:of CC ) / 2
; remove decimals, pass it to the wolf sheep predation model and change the time
ls:ask WSP [
set grass-regrowth-time round new-regrowth-time
]
; finally ask both models to go
ls:ask ls:models [ go ]
A general Usecase: Tidying up “Dead” Child Models
As previously mentioned, it is important to keep track of “living” and “dead” models when
you dynamically create and dispose of models. Let us imagine we have some lists of
models of different kinds, and we want to make sure that we only keep the models that are
alive. After running code that kills child models we can use the ls:model-exists? primitive
to clean up our list of models like this:
to-report remove-dead-models [list-of-models]
report filter [ [ model-id ] -> ls:model-exists model-id] list-of-models
end
We then reassign each list of models with this, e.g.
set a-list-of-models remove-dead-models a-list-of-models
set another-list-of-models remove-dead-models a-list-of-models
Citing LevelSpace in Research
If you use LevelSpace in research, we ask that you cite us,
Hjorth, A. Head, B. & Wilensky, U. (2015). “LevelSpace NetLogo extension”.
http://ccl.northwestern.edu/rp/levelspace/index.shtml Evanston, IL: Center for Connected
Learning and Computer Based Modeling, Northwestern University.
Primitives
Commanding and Reporting
ls:ask ls:of ls:report ls:with ls:let
Logic and Control
ls:models ls:show ls:show-all ls:hide ls:hide-all ls:path-of ls:name-of ls:model-exists?
Opening and Closing Models
ls:create-models ls:create-interactive-models ls:close ls:reset
ls:create-models
ls:create-models number path
ls:create-models number path anonymous command
Create the specified number of instances of the given .nlogo model. The path can be
absolute, or relative to the main model. Compared with ls:create-interactive-models , this
primitive creates lightweight models that are hidden by default. You should use this
primitive if you plan on having many instances of the given model. The models may be
shown using ls:show ; when visible, they will have a view and command center, but no
other widgets, e.g. plots or monitors.
If given a command, LevelSpace will call the command after loading each instance of the
model with the model-id as the argument. This allows you to easily store model ids in a
variable or list when loading models, or do other initialization. For example, to store a
model id in a variable, you can do:
let model-id 0
(ls:create-models "My-Model.nlogo" [ [id] -> set model-id id ])
ls:create-interactive-models
ls:create-interactive-models number path
ls:create-interactive-models number path anonymous command
Like ls:create-models, creates the specified number of instances of the given .nlogo
model. Unlike ls:create-models, ls:create-interactive-models creates models that are
visible by default, and have all widgets. You should use this primitive if you plan on having
only a handful of instances of the given model, and would like to be able to interact with the
instances through their interfaces during runtime.
ls:close
ls:close model-or-list-of-models
Close the model or models with the given model-id .
ls:reset
ls:reset
Close down all child models (and, recursively, their child models). You’ll often want to call
this in your setup procedure.
Note that clear-all does not close LevelSpace models.
ls:ask
ls:ask model-or-list-of-models command argument
Ask the given child model or list of child models to run the given command. This is the
primary of doing things with child models. For example:
ls:ask model-id [ create-turtles 5 ]
You can also ask a list of models to all do the same thing:
ls:ask ls:models [ create-turtles 5 ]
You may supply the command with arguments, just like you would with anonymous
commands:
let turtle-id 0
let speed 5
(ls:ask model-id [ [t s] -> ask turtle t [ fd s ] ] turtle-id speed)
Note that the commands cannot access variables in the parent model directly. You must
either pass information in through arguments or using ls:let.
ls:of
reporter ls:of model-or-list-of-models
Run the given reporter in the given model and report the result.
is designed to work like NetLogo’s inbuilt of: If you send ls:of a model-id , it will
report the value of the reporter from that model. If you send it a list of model-ids, it will
ls:of
report a list of values of the reporter string from all models. You cannot pass arguments to
ls:of, but you can use ls:let.
[ count turtles ] ls:of model-id
ls:report
ls:report model-or-list-of-models reporter argument
Run the given reporter in the given model and report the result. This form exists to allow
you to pass arguments to the reporter.
let turtle-id 0
(ls:report model-id [ [a-turtle] -> [ color ] of turtle a-turtle ] turtle-id)
ls:with
list-of-models ls:with reporter
Reports a new list of models containing only those models that reporttrue when they run
the reporter block.
ls:models ls:with [ count turtles > 100 ]
ls:let
ls:let variable-name value
Creates a variable containing the given data that can be accessed by the child models.
ask turtles [
ls:let my-color color
ls:ask my-model [
ask turtles [ set color my-color ]
]
]
ls:let
works quite similar to let in that the variable is only locally accessible:
ask turtles [
ls:let my-color color
]
;; my-color is innaccessible here
ls:let
is very similar to let, except in a few cases.
ls:let
will overwrite previous values in the variable
If you do
ls:let my-var 5
ls:let my-var 6
my-var will
ls:let
be set equal to 6. There is no ls:set.
supports variable shadowing
If you do
ls:let my-var 5
ask turtles [
ls:let my-var 6
ls:ask child-model [ show my-var ]
]
ls:ask child-model [ show my-var ]
child-model
will show 6 and then 5. This is known as variable shadowing.
The parent model cannot directly read the value of an ls variable
For example, this does not work.
ls:let my-var 5
show my-var
This is intentional. ls variables are meant to be used for sharing data with child models. The
parent model already has access to the data.
Furthermore, changing the value of an ls let variable in a child model will not affect it in any
other model. For example:
ls:let my-var 0
ls:ask ls:models [
set my-var my-var + 1
show my-var
]
All models will print 1.
ls:let
does not respect the scope of if, when, and repeat
This behavior should be considered a bug and not relied upon. It is an unfortunate
consequence of the way the NetLogo engine works. Hopefully, we’ll be able to correct this
in a future version of NetLogo.
For example, this is allowable:
if true [
ls:let my-var 5
]
ls:ask child-model [ create-turtles my-var ]
The scope of ask is respected, however.
ls:models
ls:models
Report a list of model-ids for all existing models.
ls:show
ls:show model-or-list-of-models
Makes all of the given models visible.
ls:show-all
ls:show-all model-or-list-of-models
Makes all of the given models and their descendents visible.
ls:hide
ls:hide model-or-list-of-models
Hide all of the given models. Hiding models is a good way of making your simulation run
faster.
ls:hide-all
ls:hide-all model-or-list-of-models
Hide all of the given models and their descendents. Hiding models is a good way of making
your simulation run faster.
ls:path-of
ls:path-of model-or-list-of-models
Report the full path, including the .nlogo file name, of the model. If a list of models is given,
a list of paths is reported.
ls:name-of
ls:name-of model-or-list-of-models
Reports the name of the .nlogo file of the model. This is the name of the window in which
the model appears when visible. If a list of models is given, a list of names is reported.
ls:model-exists?
ls:model-exists? model-or-list-of-models
Report a boolean value for whether there is a model with that model-id. This is often useful
when you are dynamically generating models, and want to ensure that you are not asking
models that no longer exist to do stuff.
NetLogo Matrix Extension
Using
The matrix extension adds a new matrix data structure to NetLogo. A matrix is a mutable 2-dimensional array containing
only numbers.
When to Use
Although matrices store numbers, much like a list of lists, or an array of arrays, the primary reason to use the matrix data
type is to take advantage of special mathematical operations associated with matrices. For instance, matrix multiplication
is a convenient way to perform geometric transformations, and the repeated application of matrix multiplication can also
be used to simulate other dynamic processes (for instance, processes on graph/network structures).
If you’d like to know more about matrices and how they can be used, you might consider a course on linear algebra, or
search the web for tutorials. The matrix extension also allows you to solve linear algebraic equations (specified in a
matrix format), and even to identify trends in your data and perform linear (ordinary least squares) regressions on data
sets with multiple explanatory variables.
How to Use
The matrix extension comes preinstalled.
To use the matrix extension in your model, add a line to the top of your Code tab:
extensions [matrix]
If your model already uses other extensions, then it already has anextensions line in it, so just add matrix to the list.
Example
let m matrix:from-row-list [[1 2 3] [4 5 6]]
print m
=> {{matrix: [ [ 1 2 3 ][ 4 5 6 ] ]}}
print matrix:pretty-print-text m
=>
[[ 1 2 3 ]
[ 4 5 6 ]]
print matrix:dimensions m
=> [2 3]
;;(NOTE: row & column indexing starts at 0, not 1)
print matrix:get m 1 2 ;; what number is in row 1, column 2?
=> 6
matrix:set m 1 2 10 ;; change the 6 to a 10
print m
=> {{matrix: [ [ 1 2 3 ][ 4 5 10 ] ]}}
let m2 matrix:make-identity 3
print m2
=> {{matrix: [ [ 1 0 0 ][ 0 1 0 ][ 0 0 1 ] ]}}
print matrix:times m m2 ;; multiplying by the identity changes nothing
=> {{matrix: [ [ 1 2 3 ][ 4 5 10 ] ]}}
;; make a new matrix with the middle 1 changed to -1
let m3 (matrix:set-and-report m2 1 1 -1)
print m3
=> {{matrix: [ [ 1 0 0 ][ 0 -1 0 ][ 0 0 1 ] ]}}
print matrix:times m m3
=> {{matrix: [ [ 1 -2 3 ][ 4 -5 10 ] ]}}
print matrix:to-row-list (matrix:plus m2 m3)
=> [[2 0 0] [0 0 0] [0 0 2]]
Primitives
Matrix creation and conversion to/from lists
matrix:make-constant matrix:make-identity matrix:from-row-list matrix:from-column-list matrix:to-row-list
matrix:to-column-list matrix:copy matrix:pretty-print-text
Advanced features
matrix:solve matrix:forecast-linear-growth matrix:forecast-compound-growth matrix:forecast-continuous-growth
matrix:regress
Matrix data retrieval and manipulation
matrix:get matrix:get-row matrix:get-column matrix:set matrix:set-row matrix:set-column matrix:swap-rows
matrix:swap-columns matrix:set-and-report matrix:dimensions matrix:submatrix matrix:map
Math operations
matrix:times-scalar matrix:times matrix:* matrix:times-element-wise matrix:plus-scalar matrix:plus matrix:+
matrix:minus matrix:- matrix:inverse matrix:transpose matrix:real-eigenvalues matrix:imaginary-eigenvalues
matrix:eigenvectors matrix:det matrix:rank matrix:trace
matrix:make-constant
matrix:make-constant n-rows n-cols initialValue
Reports a new n-rows by n-cols matrix object, with all entries in the matrix containing the same value (number).
matrix:make-identity
matrix:make-identity size
Reports a new square matrix object (with dimensions n-size x n-size), consisting of the identity matrix (1s along the main
diagonal, 0s elsewhere).
matrix:from-row-list
matrix:from-row-list nested-list
Reports a new matrix object, created from a NetLogo list, where each item in that list is another list (corresponding to
each of the rows of the matrix.)
print matrix:from-row-list [[1 2] [3 4]]
=> {{matrix: [ [ 1 2 ][ 3 4 ] ]}}
;; Corresponds to this matrix:
;; 1 2
;; 3 4
matrix:from-column-list
matrix:from-column-list nested-list
Reports a new matrix object, created from a NetLogo list containing each of thecolumns of the matrix.
matrix:to-row-list
matrix:to-row-list matrix
Reports a list of lists, containing each row of the matrix.
matrix:to-column-list
matrix:to-column-list matrix
Reports a list of lists, containing each column of the matrix.
matrix:copy
matrix:copy matrix
Reports a new matrix that is an exact copy of the given matrix. This primitive is important because the matrix type is
mutable (changeable). Here’s a code example:
let m1 matrix:from-column-list [[1 4 7][2
print m1
=> {{matrix: [ [ 1 2 3 ][ 4 5 6 ][ 7 8 9
let m2 m1 ;; m2 refers to the same matrix
let m3 matrix:copy m1 ;; m3 is a new copy
5 8][3 6 9]] ; a 3x3 matrix
] ]}}
object as m1
containing m1's data
matrix:set m1 0 0 100 ;; now m1 is changed
print m1
=> {{matrix:
[ [ 100 2 3 ][ 4 5 6 ][ 7 8 9 ] ]}}
print m2
=> {{matrix: [ [ 100 2 3 ][ 4 5 6 ][ 7 8 9 ] ]}}
;;Notice that m2 was also changed, when m1 was changed!
print m3
=> {{matrix:
[ [ 1 2 3 ][ 4 5 6 ][ 7 8 9 ] ]}}
matrix:pretty-print-text
matrix:pretty-print-text matrix
Reports a string that is a textual representation of the matrix, in a format that is reasonably human-readable when
displayed.
matrix:get
matrix:get matrix row-i col-j
Reports the (numeric) value at location row-i (second argument), col-j (third argument), in the given matrix given in the
first argument
matrix:get-row
matrix:get-row matrix row-i
Reports a simple (not nested) NetLogo list containing the elements ofrow-i (second argument) of the matrix supplied in
the first argument.
matrix:get-column
matrix:get-column matrix col-j
Reports a simple (not nested) NetLogo list containing the elements ofcol-j of the matrix supplied in the first argument.
matrix:set
matrix:set matrix row-i col-j new-value
Changes the given matrix by setting the value at location row-i, col-j to new-value
matrix:set-row
matrix:set-row matrix row-i simple-list
Changes the given matrix matrix by replacing the row at row-i with the contents of the simple (not nested) NetLogo list
simple-list. The simple-list must have a length equal to the number of columns in the matrix, i.e., the matrix row length.
matrix:set-column
matrix:set-column matrix col-j simple-list
Changes the given matrix matrix by replacing the column at col-j with the contents of the simple (not nested) NetLogo list
simple-list. The simple-list must have a length equal to the number of rows in the matrix, i.e., the matrix column length
length.
matrix:swap-rows
matrix:swap-rows matrix row1 row2
Changes the given matrix matrix by swapping the rows at row1 and row2 with each other.
matrix:swap-columns
matrix:swap-columns matrix col1 col2
Changes the given matrix matrix by swapping the columns at col1 and col2 with each other.
matrix:set-and-report
matrix:set-and-report matrix row-i col-j new-value
Reports a new matrix, which is a copy of the given matrix except that the value atrow-i,*col-j* has been changed to newvalue. A NetLogo statement such as set mat matrix:set-and-report mat 2 3 10 will result in mat pointing to this new
matrix, a copy of the old version of mat with the element at row 2, column 3 being set to 10. The old version of mat will be
“lost”.
matrix:dimensions
matrix:dimensions matrix
Reports a 2-element list ([num-rows,num-cols]), containing the number of rows and number of columns in the given
matrix
matrix:submatrix
matrix:submatrix matrix r1 c1 r2 c2
Reports a new matrix object, consisting of a rectangular subsection of the given matrix. The rectangular region is from
row r1 up to (but not including) row r2, and from column c1 up to (but not including) column c2.
Here is an example:
let m matrix:from-row-list [[1 2 3][4 5 6][7 8 9]]
print matrix:submatrix m 0 1 2 3 ; matrix, row-start, col-start, row-end, col-end
; rows from 0 (inclusive) to 2 (exclusive),
; columns from 1 (inclusive) to 3 (exclusive)
=> {{matrix: [ [ 2 3 ][ 5 6 ] ]}}
matrix:map
matrix:map anonymous reporter matrix
matrix:map anonymous reporter matrix anything
Reports a new matrix which results from applying reporter (an anonymous reporter or the name of a reporter) to each of
the elements of the given matrix. For example,
matrix:map sqrt matrix
would take the square root of each element of matrix. If more than one matrix argument is provided, the reporter is given
the elements of each matrix as arguments. Thus,
(matrix:map + matrix1 matrix2)
would add matrix1 and matrix2.
This reporter is meant to be the same asmap, but for matrices instead of lists.
matrix:times-scalar
matrix:times-scalar matrix factor
As of NetLogo 5.1, matrix:times can multiply matrices by scalars making this function obsolete. Usematrix:times
instead.
Reports a new matrix, which is the result of multiplying every entry in the originalmatrix by the given scaling factor.
matrix:times
matrix:times m1 m2
matrix:times m1 m2 ...
Reports a matrix, which is the result of multiplying the given matrices and scalars (using standard matrix multiplication –
make sure your matrix dimensions match up.) Without parentheses, it takes two arguments. With parentheses it takes
two or more. The arguments may either be numbers or matrices, but at least one must be a matrix.
matrix:*
m1 matrix:* m2
Reports a matrix, which is the result of multiplying the given matrices and/or scalars (using standard matrix multiplication
– make sure your matrix dimensions match up.) This is exactly the same as matrix:times m1 m2
Takes precedence over matrix:+ and matrix:-, same as normal multiplication.
matrix:times-element-wise
matrix:times-element-wise m1 m2
Reports a matrix, which is the result of multiplying the given matrices together, element-wise. All elements are multiplied
by scalar arguments as well. Note that all matrix arguments must have the same dimensions. Without parentheses, it
takes two arguments. With parentheses it takes two or more. The arguments may either be numbers or matrices, but at
least one must be a matrix.
matrix:plus-scalar
matrix:plus-scalar matrix number
As of NetLogo 5.1, matrix:plus can add matrices and scalars making this function obsolete. Use matrix:plus instead.
Reports a matrix, which is the result of adding the constantnumber to each element of the given matrix.
matrix:plus
matrix:plus m1 m2
matrix:plus m1 m2 ...
Reports a matrix, which is the result of adding the given matrices and scalars. Scalars are added to each element.
Without parentheses, it takes two arguments. With parentheses it takes two or more. The arguments may either be
numbers or matrices, but at least one must be a matrix.
matrix:+
m1 matrix:+ m2
Reports a matrix, which is the result of adding the given matrices and/or scalars. This is exactly the same asmatrix:plus
m1 m2
Takes precedence after matrix:*, same as normal addition.
matrix:minus
matrix:minus m1 m2
matrix:minus m1 m2 ...
Reports a matrix, which is the result of subtracting all arguments besidesm1 from m1. Scalar arguments are treated as
matrices of the same size as the matrix arguments with every element equal to that scalar. Without parentheses, it takes
two arguments. With parentheses it takes two or more. The arguments may either be numbers or matrices, but at least
one must be a matrix.
matrix:m1 matrix:- m2
Reports a matrix, which is the result of subtracting the given matrices and/or scalars. This is exactly the same as
matrix:minus m1 m2
Takes precedence after matrix:*, same as normal subtraction.
matrix:inverse
matrix:inverse matrix
Reports the inverse of the given matrix, or results in an error if the matrix is not invertible.
matrix:transpose
matrix:transpose matrix
Reports the transpose of the given matrix.
matrix:real-eigenvalues
matrix:real-eigenvalues matrix
Reports a list containing the real eigenvalues of the givenmatrix.
matrix:imaginary-eigenvalues
matrix:imaginary-eigenvalues matrix
Reports a list containing the imaginary eigenvalues of the givenmatrix.
matrix:eigenvectors
matrix:eigenvectors matrix
Reports a matrix that contains the eigenvectors of the given matrix. (Each eigenvector as a column of the resulting
matrix.)
matrix:det
matrix:det matrix
Reports a the determinant of the matrix.
matrix:rank
matrix:rank matrix
Reports the effective numerical rank of the matrix,obtained from SVD (Singular Value Decomposition).
matrix:trace
matrix:trace matrix
Reports the trace of the matrix, which is simply the sum of the main diagonal elements.
matrix:solve
matrix:solve A C
Reports the solution to a linear system of equations, specified by theA and C matrices. In general, solving a set of linear
equations is akin to matrix division. That is, the goal is to find a matrix B such that A * B = C. (For simple linear systems,
C and B can both be 1-dimensional matrices – i.e. vectors). If A is not a square matrix, then a “least squares” solution is
returned.
;; To solve the set of equations x + 3y = 10 and 7x - 4y = 20
;; We make our A matrix [[1 3][7 -4]], and our C matrix [[10][20]]
let A matrix:from-row-list [[1 3][7 -4]]
let C matrix:from-row-list [[10][20]]
print matrix:solve A C
=> {{matrix: [ [ 4 ][ 2.0000000000000004 ] ]}}
;; NOTE: as you can see, the results may be only approximate
;; (In this case, the true solution should be x=4 and y=2.)
matrix:forecast-linear-growth
matrix:forecast-linear-growth data-list
Reports a four-element list of the form:
[ forecast constant slope R 2 ]
The forecast is the predicted next value that would follow in the sequence given by thedata-list input, based on a linear
trend-line. Normally data-list will contain observations on some variable, Y, from time t = 0 to time t = (n-1) where n is the
number of observations. The forecast is the predicted value of Y at t = n. Theconstant and slope are the parameters of
the trend-line
Y = *constant* + *slope* * t.
2 = 1 being a perfect fit and an R2 of 0
The R 2 value measures the goodness of fit of the trend-line to the data, with an R
indicating no discernible trend. Linear growth assumes that the variable Y grows by a constant absolute amount each
period.
;; a linear extrapolation of the next item in the list.
print matrix:forecast-linear-growth [20 25 28 32 35 39]
=> [42.733333333333334 20.619047619047638 3.6857142857142824 0.9953743395474031]
;; These results tell us:
;; * the next predicted value is roughly 42.7333
;; * the linear trend line is given by Y = 20.6190 + 3.6857 * t
;; * Y grows by approximately 3.6857 units each period
;; * the R^2 value is roughly 0.9954 (a good fit)
matrix:forecast-compound-growth
matrix:forecast-compound-growth data-list
Reports a four-element list of the form:
[ forecast constant growth-proportion R 2 ]
Whereas matrix:forecast-linear-growth assumes growth by a constant absolute amount each period,matrix:forecastcompound-growth assumes that Y grows by a constant proportion each period. The constant and growth-proportion are
the parameters of the trend-line
Y = *constant* * *growth-proportion* t .
Note that the growth proportion is typically interpreted as growth-proportion = (1.0 + growth-rate). Therefore, if
matrix:forecast-compound-growth returns a growth-proportion of 1.10, that implies that Y grows by (1.10 - 1.0) = 10%
each period. Note that if growth is negative, matrix:forecast-compound-growth will return a growth-proportion of less than
one. E.g., a growth-proportion of 0.90 implies a growth rate of -10%.
NOTE: The compound growth forecast is achieved by taking the ln of Y. (Seematrix:regress, below.) Because it is
impossible to take the natural log of zero or a negative number, matrix:forecast-compound-growth will result in an error if
it finds a zero or negative number in data-list.
;; a compound growth extrapolation of the next item in the list.
print matrix:forecast-compound-growth [20 25 28 32 35 39]
=> [45.60964465307147 21.15254147944863 1.136621034423892 0.9760867518334806]
;; These results tell us:
;; * the next predicted value is approximately 45.610
;; * the compound growth trend line is given by Y = 21.1525 * 1.1366 ^ t
;; * Y grows by approximately 13.66% each period
;; * the R^2 value is roughly 0.9761 (a good fit)
matrix:forecast-continuous-growth
matrix:forecast-continuous-growth data-list
Reports a four-element list of the form:
*growth-rate* *R2 * ] . Whereas matrix:forecast-compound-growth assumes discrete time with Y
growing by a given proportion each finite period of time (e.g., a month or a year), matrix:forecast-continuous-growth
assumes that Y is compounded continuously (e.g., each second or fraction of a second). Theconstant and growth-rate
are the parameters of the trend-line
[ forecast constant
Y = *constant* * e (growth-rate * t)
matrix:forecast-continuous-growth is the “calculus” analog of matrix:forecast-compound-growth. The two will normally
yield similar (but not identical) results, as shown in the example below. growth-rate may, of course, be negative.
NOTE: The continuous growth forecast is achieved by taking the ln of Y. (Seematrix:regress, below.)
Because it is impossible to take the natural log of zero or a negative number, matrix:forecast-continuousgrowth will result in an error if it finds a zero or negative number indata-list.
;; a continuous growth extrapolation of the next item in the list.
print matrix:forecast-continuous-growth [20 25 28 32 35 39]
=> [45.60964465307146 21.15254147944863 0.12805985615332668 0.9760867518334806]
;; These results tell us:
;; * the next predicted value is approximately 45.610
;; * the compound growth trend line is given by Y = 21.1525 * e ^ (0.1281 * t)
;; * Y grows by approximately 12.81% each period if compounding takes place continuously
;; * the R^2 value is roughly 0.9761 (a good fit)
matrix:regress
matrix:regress data-matrix
All three of the forecast primitives above are just special cases of performing an OLS (ordinary-least-squares) linear
regression – the matrix:regress primitive provides a flexible/general-purpose approach. The input is a matrix data-matrix,
with the first column being the observations on the dependent variable and each subsequent column being the
observations on the (1 or more) independent variables. Thus each row consists of an observation of the dependent
variable followed by the corresponding observations for each independent variable.
The output is a Logo nested list composed of two elements. The first element is a list containing the regression constant
followed by the coefficients on each of the independent variables. The second element is a 3-element list containing the
R 2 statistic, the total sum of squares, and the residual sum of squares. The following code example shows how the
matrix:regress primitive can be used to perform the same function as the code examples shown in the matrix:forecast-*growth primitives above. (However, keep in mind that the matrix:regress primitive is more powerful than this, and can
have many more independent variables in the regression, as indicated in the fourth example below.)
;; this is equivalent to what the matrix:forecast-linear-growth does
let data-list [20 25 28 32 35 39]
let indep-var (n-values length data-list [ x -> x ]) ; 0,1,2...,5
let lin-output matrix:regress matrix:from-column-list (list data-list indep-var)
let lincnst item 0 (item 0 lin-output)
let linslpe item 1 (item 0 lin-output)
let linR2
item 0 (item 1 lin-output)
;;Note the "6" here is because we want to forecast the value at time t=6.
print (list (lincnst + linslpe * 6) (lincnst) (linslpe) (linR2))
;; this is equivalent to what the matrix:forecast-compound-growth does
let com-log-data-list (map ln [20 25 28 32 35 39])
let com-indep-var2 (n-values length com-log-data-list [ x -> x ]) ; 0,1,2...,5
let com-output matrix:regress matrix:from-column-list (list com-log-data-list com-indep-var2)
let comcnst exp item 0 (item 0 com-output)
let comprop exp item 1 (item 0 com-output)
let comR2
item 0 (item 1 com-output)
;;Note the "6" here is because we want to forecast the value at time t=6.
print (list (comcnst * comprop ^ 6) (comcnst) (comprop) (comR2))
;; this is equivalent to what the matrix:forecast-continuous-growth does
let con-log-data-list (map ln [20 25 28 32 35 39])
let con-indep-var2 (n-values length con-log-data-list [ x -> x ]) ; 0,1,2...,5
let con-output matrix:regress matrix:from-column-list (list con-log-data-list con-indep-var2)
let concnst exp item 0 (item 0 con-output)
let conrate
item 1 (item 0 con-output)
let conR2
item 0 (item 1 con-output)
print (list (concnst * exp (conrate * 6)) (concnst) (conrate) (conR2))
;; example of a regression with two independent variables:
;; Pretend we have a dataset, and we want to know how well happiness
;; is correlated to snack-food consumption and accomplishing goals.
let happiness [2 4 5 8 10]
let snack-food-consumed [3 4 3 7 8]
let goals-accomplished [2 3 5 8 9]
print matrix:regress matrix:from-column-list (list happiness snack-food-consumed goals-accomplished)
=> [[-0.14606741573033788 0.3033707865168543 0.8202247191011234] [0.9801718440185063 40.8 0.8089887640449439]]
;; linear regression: happiness = -0.146 + 0.303*snack-food-consumed + 0.820*goals-accomplished
;; (Since the 0.820 coefficient is higher than the 0.303 coefficient, it appears that each goal
;; accomplished yields more happiness than does each snack consumed, although both are positively
;; correlated with happiness.)
;; Also, we see that R^2 = 0.98, so the two factors together provide a good fit.
NetLogo Nw Extension
Usage
The first thing that one needs to understand in order to work with the network extension is how to tell the extension
which network to work with. Consider the following example situation:
breed [ bankers banker ]
breed [ clients client ]
undirected-link-breed [ friendships friendship ]
directed-link-breed [ accounts account ]
Basically, you have bankers and clients. Clients can have accounts with bankers. Bankers can probably have
account with other bankers, and anyone can be friends with anyone.
Now we might want to consider this whole thing as one big network. If that is the case, there is nothing special to do:
by default, the NW extension primitives consider all turtles and all links to be part of the current network.
We could also, however, be only interested in a subset of the network. Maybe we want to consider only friendship
relations. Furthermore, maybe we want to consider only the friendships between bankers. After all, having a very
high centrality in a network of banker friendships is very different from having a high centrality in a network of client
friendships.
To specify such networks, we need to tell the extensionboth which turtles and which links we are interested in. All
the turtles from the specified set of turtles will be included in the network, and only the links from the specified set of
links that are between turtles of the specified set will be included. For example, if you ask for bankers and
friendships, even the lonely bankers with no friends will be included, but friendship links between bankers and
clients will not be included. The way to tell the extension about this is with thenw:set-context primitive, which you
must call prior to doing any operations on a network.
Some examples:
nw:set-context turtles links
will give you everything: bankers and clients, friendships and accounts, as one big
network.
nw:set-context turtles friendships
will give you all the bankers and clients and friendships between any of
them.
nw:set-context bankers friendships will give you
nw:set-context bankers links will give you all the
all the bankers, and only friendships between bankers.
bankers, and any links between them, whether these links are
friendships or accounts.
will give you all the clients, and accounts between each other, but since in our
fictional example clients can only have accounts with bankers, this will be a completely disconnected network.
nw:set-context clients accounts
Special agentsets vs normal agentsets
It must be noted that NetLogo has two types of agentsets that behave slightly differently, and that this has an impact
on the way nw:set-context works. We will say a few words about these concepts here but, for a thorough
understanding, it is highly recommended that you read the section on agentsets in the NetLogo programming guide.
The “special” agentsets in NetLogo are turtles , links and the different “breed” agentsets. What is special about
them is that they can grow: if you create a new turtle, it will be added to the turtles agentset. If you have a bankers
breed and you create a new banker, it will be added to the bankers agentset and to the turtles agentset. Same goes
for links. Other agentsets, such as those created with the with primitive (e.g., turtles with [ color = red ] ) or the
turtle-set and link-set primitives) are never added to. The content of normal agentsets will only change if the
agents that they contain die.
To show how different types of agentsets interact withnw:set-context , let’s create a very simple network:
clear-all
create-turtles 3 [ create-links-with other turtles ]
Let’s set the context to turtles and links (which is the default anyway) and use nw:get-context to see what we
have:
nw:set-context turtles links
show map sort nw:get-context
We get all three turtles and all three links:
[[(turtle 0) (turtle 1) (turtle 2)] [(link 0 1) (link 0 2) (link 1 2)]]
Now let’s kill one turtle:
ask one-of turtles [ die ]
show map sort nw:get-context
As expected, the context is updated to reflect the death of the turtle and of the two links that died with it:
[[(turtle 0) (turtle 1)] [(link 0 1)]]
What if we now create a new turtle?
create-turtles 1
show map sort nw:get-context
Since our context is using the special turtles agentset, the new turtle is automatically added:
[[(turtle 0) (turtle 1) (turtle 3)] [(link 0 1)]]
Now let’s demonstrate how it works with normal agentsets. We start over with a new network of red turtles:
clear-all
create-turtles 3 [
create-links-with other turtles
set color red
]
And we set the context to turtles with [ color = red ]) and links
nw:set-context (turtles with [ color = red ]) links
show map sort nw:get-context
Since all turtles are red, we get everything in our context:
[[(turtle 0) (turtle 1) (turtle 2)] [(link 0 1) (link 0 2) (link 1 2)]]
But what if we ask one of them to turn blue?
ask one-of turtles [ set color blue ]
show map sort nw:get-context
No change. The agentset used in our context remains unaffected:
[[(turtle 0) (turtle 1) (turtle 2)] [(link 0 1) (link 0 2) (link 1 2)]]
If we kill one of them, however…
ask one-of turtles [ die ]
show map sort nw:get-context
It gets removed from the set:
[[(turtle 0) (turtle 2)] [(link 0 2)]]
What if we add a new red turtle?
create-turtles 1 [ set color red ]
show map sort nw:get-context
Nope:
[[(turtle 0) (turtle 2)] [(link 0 2)]]
A note regarding floating point calculations
Neither JGraphT nor Jung, the two network libraries that we use internally, usestrictfp floating point calculations.
This does mean that exact reproducibility of results involving floating point calculations between different hardware
architectures is not fully guaranteed. (NetLogo itself always uses strict math so this only applies to some primitives of
the NW extension.)
Performance
In order to be fast in as many circumstances as possible, the NW extension tries hard to never calculate things
twice. It remembers all paths, distances, and centralities that it calculates. So, while the first time you ask for the
distance between turtle 0 and turtle 3782 may take some time, after that, it should be almost instantaneous.
Furthermore, it keeps track of values it just happened to calculate along the way. For example, if turtle 297 is closer
to turtle 0 than turtle 3782 is, it may just happen to figure out the distance betweenturtle 0 and turtle 297 while
it figures out the distance between turtle 0 and turtle 3782. It will remember this value, so that if you ask it for the
distance between turtle 0 and turtle 297, it doesn’t have to do all that work again.
There are a few circumstances where the NW extension has to forget things. If the network changes at all (you add
turtles or links, or remove turtles or links), it has to forget everything. For weighted primitives, if the value of the
weight variable changes for any of the links in the network, it will forget the values associated with that weight
variable.
If you’re working on a network that can change regularly, try to do all your network calculations at once, then all your
network changes at once. The more your interweave network calculations and network changes, the more the NW
extension will have to recalculate things. For example, if you have a traffic model, and cars need to figure out the
shortest path to their destination based on the traffic each tick, have all the cars find their shortest paths, then
change the network weights to account for how traffic has changed.
There may be rare occasions in which you don’t want the NW extension to remember values. For example, if you’re
working on an extremely large network, remembering all those values may take more memory than you have. In that
case, you can just call nw:set-context (first nw:get-context) (last nw:get-context) to force the NW extension to
immediately forget everything.
Primitives
Generators
nw:generate-preferential-attachment nw:generate-random nw:generate-watts-strogatz nw:generate-small-world
nw:generate-lattice-2d nw:generate-ring nw:generate-star nw:generate-wheel
Path and Distance
nw:turtles-in-radius nw:turtles-in-reverse-radius nw:distance-to nw:weighted-distance-to nw:path-to nw:turtleson-path-to nw:weighted-path-to nw:turtles-on-weighted-path-to nw:mean-path-length nw:mean-weighted-path-length
Clusterer/Community Detection
nw:bicomponent-clusters nw:weak-component-clusters nw:louvain-communities nw:maximal-cliques nw:biggestmaximal-cliques
Context Management
nw:set-context nw:get-context nw:with-context
Import and Export
nw:save-matrix nw:load-matrix nw:save-graphml nw:load-graphml nw:load nw:save
Centrality Measures
nw:betweenness-centrality nw:eigenvector-centrality nw:page-rank nw:closeness-centrality nw:weighted-closenesscentrality
Clustering Measures
nw:clustering-coefficient nw:modularity
nw:set-context
nw:set-context turtleset linkset
Specifies the set of turtles and the set of links that the extension will consider to be the current graph. All the turtles
from turtleset and all the links from linkset that connect two turtles from turtleset will be included.
This context is used by all other primitives (unless specified otherwise) until a new context is specified. (At the
moment, only the generator primitives and the file input primitives are exceptions to this rule.)
See the usage section for a much more detailed explanation of nw:set-context .
nw:get-context
nw:get-context
Reports the content of the current graph context as a list containing two agentsets: the agentset of turtles that are
part of the context and the agentset of links that are part of the context.
Let’s say we start with a blank slate and the default context consisting ofturtles and links, nw:get-context will
report a list the special turtles and links breed agentsets:
observer> clear-all
observer> show nw:get-context
observer: [turtles links]
If we add some turtles and links to our context, we’ll still see the same thing, even thoughturtles and links have
internally grown:
observer> crt 2 [ create-links-with other turtles ]
observer> show nw:get-context
observer: [turtles links]
If you had set your context to normal agentsets instead (built withturtle-set, link-set or with) here is what you
would see:
observer>
observer>
observer>
observer:
clear-all
nw:set-context turtle-set turtles link-set links
show nw:get-context
[(agentset, 0 turtles) (agentset, 0 links)]
If you then create new turtles and links, they are not added to the context because normal agentsets don’t grow (see
Special agentsets vs normal agentsets):
observer> crt 2 [ create-links-with other turtles ]
observer> show nw:get-context
observer: [(agentset, 0 turtles) (agentset, 0 links)]
But if you construct new agentsets and set the context to them, your new agents will be there:
observer> nw:set-context turtle-set turtles link-set links
observer> show nw:get-context
observer: [(agentset, 2 turtles) (agentset, 1 link)]
If you want to see the actual content of your context, it is easy to turn your agentsets into lists that can be nicely
displayed. Just use a combination of map and sort:
observer> show map sort nw:get-context
observer: [[(turtle 0) (turtle 1)] [(link 0 1)]]
Finally, you can use nw:get-context to store a context that you eventually want to restore:
extensions [ nw ]
to store-and-restore-context
clear-all
crt 2 [
set color red
create-links-with other turtles with [ color = red ] [
set color yellow
]
]
crt 2 [
set color blue
create-links-with other turtles with [ color = blue ] [
set color green
]
]
nw:set-context turtles with [ color = red ] links with [ color = yellow ]
show map sort nw:get-context
let old-turtles item 0 nw:get-context
let old-links item 1 nw:get-context
nw:set-context turtles with [ color = blue ] links with [ color = green ]
show map sort nw:get-context
nw:set-context old-turtles old-links
show map sort nw:get-context
end
Here is the result:
observer>
observer:
observer:
observer:
store-and-restore-context
[[(turtle 0) (turtle 1)] [(link 0 1)]]
[[(turtle 2) (turtle 3)] [(link 2 3)]]
[[(turtle 0) (turtle 1)] [(link 0 1)]]
nw:with-context
nw:with-context turtleset linkset command-block
Executes the command-block with the context temporarily set to turtleset and linkset. After command-block finishes
running, the previous context will be restored.
For example:
observer>
observer>
observer:
observer>
observer:
create-turtles 3 [ create-links-with other turtles ]
nw:with-context (turtle-set turtle 0 turtle 1) (link-set link 0 1) [ show nw:get-context ]
[(agentset, 2 turtles) (agentset, 1 link)
show nw:get-context
[turtles links]
If you have NW extension code running in two forever buttons orloop blocks that each need to use different
contexts, you should use nw:with-context in each to make sure they are operating in the correct context.
nw:turtles-in-radius
nw:turtles-in-radius radius
Returns the set of turtles within the given distance (number of links followed) of the calling turtle in the current
context, including the calling turtle.
nw:turtles-in-radius form will follow both undirected
radius as “turtles who I can get to in radius steps”.
links and directed out links. You can think of turtles-in-
If you want the primitive to follow only undirected links or only directed links, you can do it by setting the context
appropriately. For example: nw:set-context turtles undir-links (assuming undir-links is an undirected link
breed) or nw:set-context turtles dir-links (assuming dir-links is a directed link breed).
Example:
clear-all
create-turtles 5
ask turtle 0 [ create-link-with turtle
ask turtle 0 [ create-link-with turtle
ask turtle 1 [ create-link-with turtle
ask turtle 2 [ create-link-with turtle
ask turtle 0 [
show sort nw:turtles-in-radius 1
]
1
2
3
4
]
]
]
]
Will output:
(turtle 0): [(turtle 0) (turtle 1) (turtle 2)]
As you may have noticed, the result includes the calling turtle. This mimics the behavior of the regular NetLogoinradius primitive.
nw:turtles-in-reverse-radius
nw:turtles-in-reverse-radius radius
Like nw:turtles-in-radius, but follows in-links instead of out-links. Also follow undirected links. You can think of
turtles-in-reverse-radius as “turtles who can get to me in radius steps”.
nw:distance-to
nw:distance-to target-turtle
Finds the shortest path to the target turtle and reports the total distance for this path, or false if no path exists in the
current context. Each link counts for a distance of one.
Example:
to go
clear-all
create-turtles
ask turtle 0 [
ask turtle 1 [
ask turtle 0 [
ask turtle 3 [
ask turtle 4 [
ask turtle 0 [
end
5
create-link-with turtle 1 ]
create-link-with turtle 2 ]
create-link-with turtle 3 ]
create-link-with turtle 4 ]
create-link-with turtle 2 ]
show nw:distance-to turtle 2 ]
Will output:
(turtle 0): 2
nw:weighted-distance-to
nw:weighted-distance-to target-turtle weight-variable
Like nw:distance-to, but takes link weight into account. The weights cannot be negative numbers.
Example:
links-own [ weight ]
to go
clear-all
create-turtles 5
ask turtle 0 [ create-link-with turtle 1 [ set weight 2.0 ]
ask turtle 1 [ create-link-with turtle 2 [ set weight 2.0 ]
ask turtle 0 [ create-link-with turtle 3 [ set weight 0.5 ]
ask turtle 3 [ create-link-with turtle 4 [ set weight 0.5 ]
ask turtle 4 [ create-link-with turtle 2 [ set weight 0.5 ]
ask turtle 0 [ show nw:weighted-distance-to turtle 2 weight
end
]
]
]
]
]
]
Will output:
(turtle 0): 1.5
nw:path-to
nw:path-to target-turtle
Finds the shortest path to the target turtle and reports the actual path between the source and the target turtle. The
path is reported as the list of links that constitute the path.
If no path exist between the source and the target turtles,false will be reported instead.
Note that the NW-Extension remembers paths that its calculated previously unless the network changes. Thus, you
don’t need to store paths to efficiently move across the network; you can just keep re-calling one of the path
primitives. If the network changes, however, the stored answers are forgotten. Example:
links-own [ weight ]
to go
clear-all
create-turtles 5
ask turtle 0 [ create-link-with turtle 1 ]
ask turtle 1 [ create-link-with turtle 2 ]
ask turtle 0 [ create-link-with turtle 3 ]
ask turtle 3 [ create-link-with turtle 4 ]
ask turtle 4 [ create-link-with turtle 2 ]
ask turtle 0 [ show nw:path-to turtle 2 ]
end
Will output:
(turtle 0): [(link 0 1) (link 1 2)]
nw:turtles-on-path-to
nw:turtles-on-path-to target-turtle
Like nw:path-to, but the turtles on the path are reported, instead of the links, including the source turtle and target
turtle.
Example:
to go
clear-all
create-turtles
ask turtle 0 [
ask turtle 1 [
ask turtle 0 [
ask turtle 3 [
ask turtle 4 [
ask turtle 0 [
end
5
create-link-with turtle 1 ]
create-link-with turtle 2 ]
create-link-with turtle 3 ]
create-link-with turtle 4 ]
create-link-with turtle 2 ]
show nw:turtles-on-path-to turtle 2 ]
Will output:
(turtle 0): [(turtle 0) (turtle 1) (turtle 2)]
nw:weighted-path-to
nw:weighted-path-to target-turtle weight-variable
Like nw:path-to, but takes link weight into account.
Example:
links-own [ weight ]
to go
clear-all
create-turtles 5
ask turtle 0 [ create-link-with turtle 1 [ set
ask turtle 1 [ create-link-with turtle 2 [ set
ask turtle 0 [ create-link-with turtle 3 [ set
ask turtle 3 [ create-link-with turtle 4 [ set
ask turtle 4 [ create-link-with turtle 2 [ set
ask turtle 0 [ show nw:weighted-path-to turtle
end
weight 2.0
weight 2.0
weight 0.5
weight 0.5
weight 0.5
2 weight ]
Will output:
(turtle 0): [(link 0 3) (link 3 4) (link 2 4)]
nw:turtles-on-weighted-path-to
nw:turtles-on-weighted-path-to target-turtle weight-variable
Like nw:turtles-on-path-to, but takes link weight into account.
]
]
]
]
]
]
]
]
]
]
Example:
links-own [ weight ]
to go
clear-all
create-turtles 5
ask turtle 0 [ create-link-with turtle 1 [ set
ask turtle 1 [ create-link-with turtle 2 [ set
ask turtle 0 [ create-link-with turtle 3 [ set
ask turtle 3 [ create-link-with turtle 4 [ set
ask turtle 4 [ create-link-with turtle 2 [ set
ask turtle 0 [ show nw:weighted-path-to turtle
end
weight 2.0
weight 2.0
weight 0.5
weight 0.5
weight 0.5
2 weight ]
]
]
]
]
]
]
]
]
]
]
Will output:
(turtle 0): [(turtle 0) (turtle 3) (turtle 4) (turtle 2)]
nw:mean-path-length
nw:mean-path-length
Reports the average shortest-path length between all distinct pairs of nodes in the current context.
Reports false unless paths exist between all pairs.
Example:
links-own [ weight ]
to go
clear-all
create-turtles 3
ask turtle 0 [ create-link-with turtle 1 [ set weight 2.0 ] ]
ask turtle 1 [ create-link-with turtle 2 [ set weight 2.0 ] ]
show nw:mean-path-length
create-turtles 1 ; create a new, disconnected turtle
show nw:mean-path-length
end
Will ouput:
observer: 1.3333333333333333
observer: false
nw:mean-weighted-path-length
nw:mean-weighted-path-length weight-variable
Like nw:mean-path-length, but takes into account link weights.
Example:
links-own [ weight ]
to go
clear-all
create-turtles 3
ask turtle 0 [ create-link-with turtle 1 [ set weight 2.0 ] ]
ask turtle 1 [ create-link-with turtle 2 [ set weight 2.0 ] ]
show nw:mean-path-length
show nw:mean-weighted-path-length weight
create-turtles 1 ; create a new, disconnected turtle
show nw:mean-path-length
show nw:mean-weighted-path-length weight
end
Will ouput:
observer: 2.6666666666666665
observer: false
nw:betweenness-centrality
nw:betweenness-centrality
To calculate the betweenness centrality of a turtle, you take every other possible pairs of turtles and, for each pair,
you calculate the proportion of shortest paths between members of the pair that passes through the current turtle.
The betweenness centrality of a turtle is the sum of these.
As of now, link weights are not taken into account.
nw:eigenvector-centrality
nw:eigenvector-centrality
The Eigenvector centrality of a node can be thought of as the amount of influence a node has on a network. In
practice, turtles that are connected to a lot of other turtles that are themselves well-connected (and so on) get a
higher Eigenvector centrality score.
In this implementation, the eigenvector centrality is normalized such that the highest eigenvector centrality a node
can have is 1. This implementation is designed to agree with Gephi’s implementation out to at least 3 decimal
places. If you discover that it disagrees with Gephi on a particular network, please report it.
The primitive respects link direction, even in mixed-directed networks. This is the one place where it should disagree
with Gephi; Gephi refuses to treat directed links as directed in mixed-networks.
As of now, link weights are not taken into account.
nw:page-rank
nw:page-rank
The page rank of a node can be thought of as the proportion of time that an agent walking forever at random on the
network would spend at this node. The agent has an equal chance of taking any of a nodes edges, and will jump
around the network completely randomly 15% of the time. In practice, like with eigenvector centrality, turtles that are
connected to a lot of other turtles that are themselves well-connected (and so on) get a higher page rank.
Page rank is one of the several algorithms that search engines use to determine the importance of a website.
The sum of all page rank values should be approximately one. Unlike eigenvector centrality, page rank is defined for
all networks, no matter the connectivity. Currently, it treats all links as undirected links.
As of now, link weights are not taken into account.
nw:closeness-centrality
nw:closeness-centrality
The closeness centrality of a turtle is defined as the inverse of the average of it’s distances to all other turtles. (Some
people use the sum of distances instead of the average, but the extension uses the average.)
Note that this primitive reports the intra-component closeness of a turtle, that is, it takes into account only the
distances to the turtles that are part of the same component as the current turtle, since distance to turtles in other
components is undefined. The closeness centrality of an isolated turtle is defined to be zero.
nw:weighted-closeness-centrality
nw:weighted-closeness-centrality link-weight-variable
This is identical to nw:closeness-centrality, except that weights provided by the given variable are treated as the
distances of links.
nw:clustering-coefficient
nw:clustering-coefficient
Reports the local clustering coefficient of the turtle. The clustering coefficient of a node measures how connected its
neighbors are. It is defined as the number of links between the node’s neighbors divided by the total number of
possible links between its neighbors.
takes the directedness of links into account. A directed link counts as a single link
whereas an undirected link counts as two links (one going one-way, one going the other).
nw:clustering-coefficient
The global clustering coefficient measures how much nodes tend to cluster together in the network in general. It is
defined based on the types of triplets in the network. A triplet consists of a central node and two of its neighbors. If its
neighbors are also connected, it’s a closed triplet. If its neighbors are not connected, it’s an open triplet. The global
clustering coefficient is simply the number of closed triplets in a network divided by the total number of triplets. It can
be calculated from the local clustering coefficient quite easily with the following code
to-report global-clustering-coefficient
let closed-triplets sum [ nw:clustering-coefficient * count my-links * (count my-links - 1) ] of turtles
let triplets sum [ count my-links * (count my-links - 1) ] of turtles
report closed-triplets / triplets
end
Note that the above will only work with the default context, and may need to tweaked if you’ve set the turtles or links
in the network to something other than turtles and links.
The average local clustering coefficient is another popular method for measuring the amount of clustering in the
network as a whole. It may be calculated with
mean [ nw:clustering-coefficient ] of turtles
nw:modularity
nw:modularity
[Modularity](https://en.wikipedia.org/wiki/Modularity_(networks)) is a measurement of community structure in the
network. It is defined based on the number of in-community links versus the number of between-community links.
This primitive takes as input a list of agentsets, where each of the agentsets is one the communities that you’re
separating the network into.
This measurement works on undirected, directed, and mixed-directedness networks. In the case of mixeddirectedness, undirected links are treated essentially the same as two opposing directed links. It does not take
weight into account.
Example:
nw:modularity (list (turtles with [ color = blue ]) (turtles with [ color = red ]))
nw:bicomponent-clusters
nw:bicomponent-clusters
Reports the list of bicomponent clusters in the current network context. A bicomponent (also known as a maximal
biconnected subgraph) is a part of a network that cannot be disconnected by removing only one node (i.e. you need
to remove at least two to disconnect it). The result is reported as a list of agentsets, in random order. Note that one
turtle can be a member of more than one bicomponent at once.
nw:weak-component-clusters
nw:weak-component-clusters
Reports the list of “weakly” connected components in the current network context. A weakly connected component is
simply a group of nodes where there is a path from each node to every other node. A “strongly” connected
component would be one where there is a directed path from each node to every other. The extension does not
support the identification of strongly connected components at the moment.
The result is reported as a list of agentsets, in random order. Note that one turtlecannot be a member of more than
one weakly connected component at once.
nw:louvain-communities
nw:louvain-communities
Detects community structure present in the network. It does this by maximizingmodularity using the Louvain method.
The communities are reported as a list of turtle-sets.
Often you’ll want to tell turtles about the community that they are in. You can do this like so:
turtles-own [ community ]
...
foreach ls:louvain-communities [ [comm] ->
ask comm [ set community comm ]
]
You can give each community its own color with something like this:
let communities ls:louvain-communities
let colors sublist 0 (length communities) base-colors
(foreach communities colors [ [community col] ->
ask community [ set color col ]
])
nw:maximal-cliques
nw:maximal-cliques
A clique is a subset of a network in which every node has a direct link to every other node. A maximal clique is a
clique that is not, itself, contained in a bigger clique.
The result is reported as a list of agentsets, in random order. Note that one turtle can be a member of more than one
maximal clique at once.
The primitive uses the Bron–Kerbosch algorithm and only works with undirected links.
nw:biggest-maximal-cliques
nw:biggest-maximal-cliques
The biggest maximal cliques are, as the name implies, the biggest cliques in the current context. Often, more than
one clique are tied for the title of biggest clique, so the result is reported as a list of agentsets, in random order. If you
want only one clique, use one-of nw:biggest-maximal-cliques .
The primitive uses the Bron–Kerbosch algorithm and only works with undirected links.
nw:generate-preferential-attachment
nw:generate-preferential-attachment turtle-breed link-breed num-nodes optional-command-block
Generates a new network using the Barabási–Albert algorithm. This network will have the property of being “scale
free”: the distribution of degrees (i.e. the number of links for each turtle) should follow a power law.
In this version of the primitive, turtles are added, one by one, each forming one link to a previously added turtle, until
num-nodes is reached. The more links a turtle already has, the greater the probability that new turtles form links with it
when they are added. Future versions of the primitive might provide more flexibility in the way the network is
generated.
If you specify an optional-command-block, it is executed for each turtle in the newly created network. For example:
nw:generate-preferential-attachment turtles links 100 [ set color red ]
nw:generate-random
nw:generate-random turtle-breed link-breed num-nodes connection-probability optional-command-block
Generates a new random network of num-nodes turtles in which each one has a connection-probability (between 0
and 1) of being connected to each other turtles. The algorithm uses the G(n, p) variant of the Erdős–Rényi model.
The algorithm is O(n²) for directed networks and O(n²/2) for undirected networks, so generating more than a couple
thousand nodes will likely take a very long time.
If you specify an optional-command-block, it is executed for each turtle in the newly created network. For example:
nw:generate-random turtles links 100 0.5 [ set color red ]
nw:generate-watts-strogatz
nw:generate-watts-strogatz turtle-breed link-breed num-nodes neighborhood-size rewire-probability
optional-command-block
Generates a new Watts-Strogatz small-world network.
The algorithm begins by creating a ring of nodes, where each node is connected toneighborhood-size nodes on
either side. Then, each link is rewired with probability rewire-prob.
If you specify an optional-command-block, it is executed for each turtle in the newly created network. Furthermore,
the turtles are generated in the order they appear as in create-ordered-turtles . So, in order to lay the ring out as a
ring, you can do something like:
nw:generate-watts-strogatz turtles links 50 2 0.1 [ fd 10 ]
nw:generate-small-world
nw:generate-small-world turtle-breed link-breed row-count column-count clustering-exponent is-toroidal
optional-command-block
Generates a new small-world network using the Kleinberg Model. Note that nw:generate-watts-strogatz generates a
more traditional small-world network.
The algorithm proceeds by generating a lattice of the given number of rows and columns (the lattice will wrap around
itself if is-toroidal is true). The “small world effect” is created by adding additional links between the nodes in the
lattice. The higher the clustering-exponent, the more the algorithm will favor already close-by nodes when adding
new links. A clustering exponent of 2.0 is typically used.
If you specify an optional-command-block, it is executed for each turtle in the newly created network. For example:
nw:generate-small-world turtles links 10 10 2.0 false [ set color red ]
The turtles are generated in the order that they appear in the lattice. So, for instance, to generate a kleinberg lattice
accross the entire world, and lay it out accordingly, try the following:
nw:generate-small-world turtles links world-width world-height 2.0 false
(foreach (sort turtles) (sort patches) [ [t p] -> ask t [ move-to p ] ])
nw:generate-lattice-2d
nw:generate-lattice-2d turtle-breed link-breed row-count column-count is-toroidal optional-command-block
Generates a new 2D lattice network (basically, a grid) of row-count rows and column-count columns. The grid will
wrap around itself if is-toroidal is true.
If you specify an optional-command-block, it is executed for each turtle in the newly created network. For example:
nw:generate-lattice-2d turtles links 10 10 false [ set color red ]
The turtles are generated in the order that they appear in the lattice. So, for instance, to generate a lattice accross
the entire world, and lay it out accordingly, try the following:
nw:generate-lattice-2d turtles links world-width world-height false
(foreach (sort turtles) (sort patches) [ [t p] -> ask t [ move-to p ] ])
nw:generate-ring
nw:generate-ring turtle-breed link-breed num-nodes optional-command-block
Generates a ring network of num-nodes turtles, in which each turtle is connected to exactly two other turtles.
The number of nodes must be at least three.
If you specify an optional-command-block, it is executed for each turtle in the newly created network. For example:
nw:generate-ring turtles links 100 [ set color red ]
nw:generate-star
nw:generate-star turtle-breed link-breed num-nodes optional-command-block
Generates a star network in which there is one central turtle and every other turtle is connected only to this central
node. The number of turtles can be as low as one, but it won’t look much like a star.
If you specify an optional-command-block, it is executed for each turtle in the newly created network. For example:
nw:generate-star turtles links 100 [ set color red ]
nw:generate-wheel
nw:generate-wheel turtle-breed link-breed num-nodes optional-command-block
Variants:
nw:generate-wheel-inward
nw:generate-wheel-outward
Generates a wheel network, which is basically a ring network with an additional “central” turtle that is connected to
every other turtle.
The number of nodes must be at least four.
The nw:generate-wheel only works with undirected link breeds. The nw:generate-wheel-inward and nw:generatewheel-outward versions only work with directed link-breed. The inward and outward part of the primitive names refer
to the direction that the “spokes” of the wheel point to relative to the central turtle.
If you specify an optional-command-block, it is executed for each turtle in the newly created network. For example:
nw:generate-wheel turtles links 100 [ set color red ]
nw:save-matrix
nw:save-matrix file-name
Saves the current network, as defined bynw:set-context , to file-name, as a text file, in the form of a simple
connection matrix.
Here is, for example, a undirected ring network with four nodes:
0.00
1.00
0.00
1.00
1.00
0.00
1.00
0.00
0.00
1.00
0.00
1.00
1.00
0.00
1.00
0.00
And here is the directed version:
0.00
0.00
0.00
1.00
1.00
0.00
0.00
0.00
0.00
1.00
0.00
0.00
0.00
0.00
1.00
0.00
At the moment, nw:save-matrix does not support link weights. Every link is represented as a “1.00” in the connection
matrix. This will change in a future version of the extension.
nw:load-matrix
nw:load-matrix file-name optional-command-block
Generates a new network according to the connection matrix saved infile-name, using turtle-breed and link-breed to
create the new turtles and links.
At the moment, nw:load-matrix does not support link weights.
Please be aware that the breeds that use use to load the matrix may be different from those that you used when you
saved it.
For example:
extensions [ nw ]
directed-link-breed [ dirlinks dirlink ]
to go
clear-all
crt 5 [ create-dirlinks-to other turtles ]
nw:set-context turtles dirlinks
nw:save-matrix "matrix.txt"
clear-all
nw:load-matrix "matrix.txt" turtles links
layout-circle turtles 10
end
…will give you back undirected links, even if you saved directed links into the matrix.
If you specify an optional-command-block, it is executed for each turtle in the newly created network. For example:
nw:load-matrix "matrix.txt" turtles links [ set color red ]
nw:save-graphml
nw:save-graphml file-name
You can save the current graph to GraphML. The following NetLogo code:
extensions [ nw ]
breed [ bankers banker ]
bankers-own [ bank-name ]
breed [ clients client ]
clients-own [ hometown ]
undirected-link-breed [ friendships friendship ]
directed-link-breed [ accounts account ]
accounts-own [ amount ]
to go
clear-all
create-bankers 1 [
set bank-name "The Bank"
]
create-clients 1 [
set hometown "Turtle City"
create-friendship-with banker 0
create-account-to banker 0 [
set amount 9999.99
]
]
nw:set-context turtles links
nw:save-graphml "example.graphml"
end
Will produce the following GraphML file:
up
0
1
default
clients
1
false
9.9
356
Turtle City
115
0
1
up
0
1
default
bankers
0
false
9.9
32
The Bank
85
0
1
(client 1)
none
(banker 0)
9.9
0
default
accounts
5
9999.99
false
(banker 0)
none
(client 1)
9.9
0
default
friendships
5
false
A few things to notice:
The breed is stored as data field, both for nodes and edges.
The data includes both NetLogo’s internal variables and the variables that were defined as eitherbreeds-own,
turtles-own, linkbreeds-own or links-own.
Each key gets an attr.type based on the actual types of the values contained in the agent variables. The three
possible types are "string", "double" and "boolean". To determine the attribute type of a particular agent variable,
the extension will look at the first agent in the graph. To see which agent is first, you can look at the result of
nw:get-context . Note that variables containing other types of values, such as turtles, patches, lists, etc., will be
stored as strings.
This example only has a directed link, and you will notice the element. If we had
only undirected links, we would have . What if we try to mix both kinds of link?
At the moment, the extension will save such a “mixed” graph as if it were an undirected graph (see this issue for
more details). The order of the source and target will be respected, however, so if you know which breeds
represent directed links, you can figure it out a posteriori.
nw:load-graphml
nw:load-graphml file-name optional-command-block
Loading a GraphML file into NetLogo with the network extension should be as simple as callingnw:load-graphml
"example.graphml" , but there is a bit of preparation involved.
The key idea is that nw:load-graphml will try to assign the attribute values defined in the GraphML file to NetLogo
agent variables of the same names (this is not case sensitive). The first one it tries to set is breed if it is there, so the
turtle or link will get the right breed and, hence, the right breed variables.
One special case is the who number, which is ignored by the importer if it is present as a GraphML attribute: NetLogo
does not allow you to modify this number once a turtle is created and, besides, there could already be an existing
turtle with that number.
The simplest case to handle is when the original GraphML file has been saved from NetLogo by usingnw:savegraphml . In this case, all you should have to do is to make sure that you have the same breed and variables
definition as when you saved the file and you should get back your original graph. For example, if you want to load
the file from the nw:save-graphml example above, you should have the following definitions:
breed [ bankers banker ]
bankers-own [ bank-name ]
breed [ clients client ]
clients-own [ hometown ]
undirected-link-breed [ friendships friendship ]
directed-link-breed [ accounts account ]
accounts-own [ amount ]
Loading a graph that was saved from a different program than NetLogo is quite possible as well, but it may take a bit
of tinkering to get all the attribute-variable match up right. If you encounter major problems, please do not hesitate to
open an issue.
The extension will try to assign the type defined byattr.type to each variable that it loads. If it’s unable to convert it
to that type, it will load it as a string. If attr.type is not defined, or is set to an unknown value, the extension will first
try to load the value as a double, then try it as a boolean, and finally fall back on a string.
If you specify an optional-command-block, it is executed for each turtle in the newly created network. For example:
nw:load-graphml "example.graphml" [ set color red ]
Note that this command block can be used to build a list or an agentset containing the newly created nodes:
let node-list []
nw:load-graphml "example.graphml" [
set node-list lput self node-list
]
let node-set turtle-set node-list
nw:load
nw:load file-name default-turtle-breed default-link-breed optional-command-block
Filetype specific variants:
nw:load
nw:load-dl
nw:load-gdf
nw:load-gexf
nw:load-gml
nw:load-vna
Import the given file into NetLogo. Likenw:load-graphml, the importer will do its best to match node and edge
attributes in the file with turtle and link variables in NetLogo. If breed is specified for nodes and edges in the file and
exists in NetLogo, it will be used. Otherwise, the default turtle and link breeds are used.
Limitations:
Multigraphs are not supported in importing. Even if the file format supports it (and many don’t), only the first link
will be used on import. This is due to a limitation in the parsing libraries NW uses. nw:load-graphml does support
multigraphs with the normal NetLogo limitation that two turtles can share more than one link only if all the links are
of different breeds.
determines the file-type of given file based on the extension and calls the correspondingload-* primitive on
it. Note that GraphML must be imported with nw:load-graphml.
nw:load
nw:save
nw:save file-name
Filetype specific variants:
nw:save-dl
nw:save-gdf
nw:save-gexf
nw:save-gml
nw:save-vna
Export the network context in the given format to the given file. Turtle and link attributes will be exported to formats
that support node and edge properties.
Limitations:
and y (not xcor and ycor) can only be numbers. x and y are commonly used in formats pertaining to position and
behind the scenes NW uses Gephi’s libraries for exporting. Furthermore, x and y will be added even if they didn’t
exist in the model. Again, this is because NW uses Gephi’s libraries which assume that nodes have positions
stored in x and y. If you wish to export to Gephi specifically, we recommend creatingx and y turtles variables and
setting them to xcor and ycor before export.
Color will be exported in a standard RGB format. This should hopefully increase compatibility with other programs.
Turtle and link variables that contain values of different types will be stored as strings. Unfortunately, most network
formats require that node and attributes have a single type.
Many programs use label to store the id of nodes. Thus, if you’re having trouble importing data exported from
NetLogo into another program, you might try setting turtles’ labels to their who number.
Multigraphs are not supported. Thus, two turtles can share at most one link.nw:save-graphml does support
multigraphs, so use that if turtles can have more than one type of link connecting them.
x
determines the file-type of the given file based on the extension and calls the correspondingsave-* primitive
on it. Note that GraphML must be exported with nw:save-graphml.
nw:save
NetLogo Palette Extension
Using the Palette Extension
The NetLogo palette extension allows to map values to colors. The colors go beyond NetLogo colors, including
ColorBrewer color schemes or arbitrary RGB colors. Additionally, it provides a primitive to map to color gradients and a
primitive to launch a ColorBrewer dialog for easy scheme selection.
Getting Started
To get started with palettes add to the top of your Code tab:
extensions [palette]
you can then call any of the primitives by adding palette: before the primitive:
palette:scale-gradient
palette:scale-scheme
palette:scheme-color
palette:scheme-dialog
The palette extension primitives return a list containing RGB colors [[r g b][r g b]...[r g b]] , except for
palette:scheme-dialog which opens a dialog.
What colors should I use ?
ColorBrewer has many colors where to start. ColorBrewer has three schemes Sequential, Divergent and Qualitative. The
use of ColorBrewer for maps is discussed at length in this paper (Harrower, Brewer 2003). Choosing the right colors is a
design problem, thus, there are many acceptable solution. However, these guidelines might be useful for choosing colors
in Agent Based Models:
Sequential colors are best for continuous natural phenomena models such as as heat diffusion in physics or fire in
earth sciences.
Divergent colors are useful for highlighting a middle value in a model. It can be also applied to the heat diffusion model
if the goal is to highlight the middle temperature.
Qualitative colors are best for choosing colors in models where color denotes category and not value.
For agents that cover large areas avoid strong colors and try to use pastel colors. However, for a low number of small
isolated agents try to use strong colors such as such a accent.
The main goal is to avoid having a large area covered with agents with a bright color and or having small areas having
a muted pastel color.
If you are coloring both turtles and patches, make sure they have different ranges of hue, saturation and value. E.g.
Use different hues of pastel for patches and accent for turtles
Should I use a continuous color gradient or just a discrete color set ?
The answer depends on the task that your will be asking from your user.
For example, gradients are more aesthetic thus are more memorable than discrete colors. Consequently, a gradient can
be a better choice for presentations where the main goal of the image is to be attractive and memorable. However,
binning values in a discrete set of colors simplifies tasks such as estimation and counting by removing unnecessary
detail to display the big picture. Thus, discrete colors can be a better choice for a paper where the user will have the time
and interest to study the visualization.
In order to see the difference you can turn on and off the gradient in the Heat Diffusion model. You can observe that
turning gradient on makes the model more aesthetic, but it becomes harder to estimate the value of a patch at a given
position.
Example Models
There is an example of using the palette primitives in the Code Examples section of the models library:
Palette Example
And one Sample Model that uses the extension:
Heat Diffusion - Alternative Gradient
Further Reading
Be sure to check the ColorBrewer web page
To get a deeper understanding of how to use the color schemes read the ColorBrewer paper (Harrower, Brewer 2003)
Primitives
palette:scale-gradient palette:scale-scheme palette:scheme-colors palette:scale-gradient
palette:scale-gradient
palette:scale-gradient rgb-color-list number range1 range2
Reports an RGB color proportional to number using a gradient generated with rgb-color-list. An rgb-color-list consist of a
list containing RGB list with three values between 0 and 255: [[r1 g1 b1] [r2 g2 b2] [r3 g3 b3] …]
If range1 is less than range2, the color will be directly mapped to gradient colors. While, ifrange2 is less than range1, the
color gradient is inverted.
If number is less than range1, then the first color of is RGB-color-list is chosen.
If number is grater than range2, then the last color of is RGB-color-list is chosen.
Example:
ask patches
[
set pcolor palette:scale-gradient [[255 0 0] [0 0 255]] pxcor min-pxcor max-pxcor
]
;; colors each patch with a color proportional to the gradient
palette:scale-scheme
palette:scale-scheme scheme-type scheme-color number-of-classes range1 range2
Reports an RGB color proportional to number using the color brewer schemes. It takes six arguments the first three
arguments define the ColorBrewer legend. Fir the user should select a scheme-type which can be “Sequential”,
“Divergent, Qualitative”. Then it should select a variety of scheme-colors which depending on the scheme-color can have
names such as “Reds”, “Divergent”, “Set1”. Finally the user should select the number of classes with a minimum of 3 and
a maximum between 9 and 11. For more information go to http://www.colorbrewer.org or consult the scheme-dialog
primitive.
If range1 is less than range2, the color will be directly mapped to scheme colors. While, ifrange2 is less than range1, the
color scheme selection is inverted.
If number is less than range1, then the first color of the resulting ColorBrewer legend is chosen.
If number is grater than range2, then the last color of the resulting ColorBrewer legend is chosen.
Example:
ask patches
[
set pcolor palette:scale-scheme [[255 0 0] [0 0 255]] pxcor min-pxcor max-pxcor
]
;; colors each patch with a color from the Color Brewer Schemes
palette:scheme-colors
palette:scheme-colors scheme-type scheme-color number-of-classes
report a list of RGB colors with the size specified in the a number of classes
Example:
show palette:scheme-colors "Divergent" "Spectral" 3
=> [[252 141 89] [255 255 191] [153 213 148]]
; The schemes-color primitive can be used with the scale-gradient primitive
ask patches
[set pcolor palette:scale-gradient palette:scheme-colors "Divergent" "Spectral" 9 pxcor min-pxcor max-pxcor]
palette:scale-gradient
palette:scale-gradient rgb-color-list number range1 range2
Reports an RGB color proportional to number using a gradient generated withrgb-color-list. An rgb-color-list consist of a
list containing RGB list with three values between 0 and 255: [[r1 g1 b1] [r2 g2 b2] [r3 g3 b3] …]
If range1 is less than range2, the color will be directly mapped to gradient colors. While, ifrange2 is less than range1, the
color gradient is inverted.
If number is less than range1, then the first color of is RGB-color-list is chosen.
If number is grater than range2, then the last color of is RGB-color-list is chosen.
Example:
ask patches
[
set pcolor palette:scale-gradient [[255 0 0] [0 0 255]] pxcor min-pxcor max-pxcor
]
;; colors each patch with a color proportional to the gradient
References
ColorBrewer http://www.colorbrewer.org
HARROWER, M. and C. BREWER (2003). ColorBrewer: An online tool for selecting color schemes for maps. The
Cartographic Journal 40(1): 27-37. )
HEALEY, C G (2006) Perception in Visualization, (comprehensive review updated regularly).
HEALEY, C G, BOOTH K S, and ENNS, J T (1995). Visualizing Real-Time Multivariate Data Using Preattentive
Processing ACM Transactions on Modeling and Computer Simulation 5, 3, 190-221.
TUFTE, E (1983) The Visual Display of Quantitative Information , Graphics Press.
WARE, C (2004) Information Visualization, 2nd Ed., Morgan Kaufmann. Feedback
NetLogo Profiler Extension
Using the Profiler Extension
If you’d like your model to run faster, the profiler extension may be useful to you. It
includes primitives that measure how many times the procedures in your model are called
during a run and how long each call takes. You can use this information to where to focus
your speedup efforts.
Caution:
The profiler extension is experimental. It is not yet well tested or user friendly.
Nonetheless, we think some users will find it useful.
How to use
The profiler extension comes preinstalled. To use the extension in your model, add a line
to the top of your Code tab:
extensions [profiler]
If your model already uses other extensions, then it already has anextensions line in it, so
just add profiler to the list.
For more information on using NetLogo extensions, see theExtensions Guide
Example
setup
profiler:start
repeat 20 [ go ]
profiler:stop
print profiler:report
profiler:reset
;;
;;
;;
;;
;;
;;
set up the model
start profiling
run something you want to measure
stop profiling
view the results
clear the data
Thanks to Roger Peppe for his contributions to the code.
Primitives
profiler:calls profiler:exclusive-time profiler:inclusive-time profiler:start
profiler:stop profiler:reset profiler:report
profiler:calls
profiler:calls procedure-name
Reports the number of times that procedure-name was called. If procedure-name is not
defined, then reports 0.
profiler:exclusive-time
profiler:exclusive-time procedure-name
Reports the exclusive time, in milliseconds, that procedure-name was running for.
Exclusive time is the time from when the procedure was entered, until it finishes, but does
not include any time spent in other user-defined procedures which it calls.
If procedure-name is not defined, then reports 0.
profiler:inclusive-time
profiler:inclusive-time procedure-name
Reports the inclusive time, in milliseconds, that procedure-name was running for. Inclusive
time is the time from when the procedure was entered, until it finishes.
If procedure-name is not defined, then reports 0.
profiler:start
profiler:start
Instructs the profiler to begin recording user-defined procedure calls.
profiler:stop
profiler:stop
Instructs the profiler to stop recording user-defined procedure calls.
profiler:reset
profiler:reset
Instructs the profiler to erase all collected data.
profiler:report
profiler:report
Reports a string containing a breakdown of all user-defined procedure calls. TheCalls
column contains the number of times a user-defined procedure was called. The Incl
T(ms) column is the total time, in milliseconds, it took for the call to complete, including the
time spent in other user-defined procedures. The Excl T(ms) column is the total time, in
milliseconds, spent within that user-defined procedure, not counting other user-define
procedures it called. The Excl/calls column is an estimate of the time, in milliseconds,
spent in that user-defined procedure for each call.
Here is example output:
Sorted by Exclusive Time
Name
Calls Incl T(ms) Excl T(ms) Excl/calls
CALLTHEM
CALLME
REPORTME
13
13
13
26.066
6.413
0.177
19.476
6.413
0.177
1.498
0.493
0.014
Sorted by Inclusive Time
Name
CALLTHEM
CALLME
REPORTME
Calls Incl T(ms) Excl T(ms) Excl/calls
13
26.066
19.476
1.498
13
6.413
6.413
0.493
13
0.177
0.177
0.014
Sorted by Number of Calls
Name
CALLTHEM
Calls Incl T(ms) Excl T(ms) Excl/calls
13
26.066
19.476
1.498
NetLogo R Extension
The R-Extension of NetLogo provides primitives to use the statistical software R (Gnu S) (seethe R Project website) within a
NetLogo model. There are primitives to create R-Variables with values from NetLogo variables or agents and others to
evaluate commands in R with and without return values.
Using
To use the extension in your model, add a line to the top of your procedures tab:
extensions [ r ]
If your model already uses other extensions, then it already has anextensions line in it, so just add r to the list.
For more information on using NetLogo extensions, see theExtensions Guide.
For examples of the usage of the R-Extension, models can be downloadedfrom the project repository. These models are
installed with NetLogo in the “models” directory of the R extension. Please note that (as of NetLogo 6.0) these models are
not included in the NetLogo models library.
Some Tips
Plotting
If you want to use the plot function of R, you could activate the JavaGD plot device viar:setPlotDevice, see the “plotexample1.nlogo” model. This is the prefered method!
But you can also use the standard R device, but then, you have to give R some cpu time, e.g. by run an evalulation of
sys.sleep(0.01) with a forever button. See the “plot-example2.nlogo”. (Many thanks to Thomas Petzold!). The creation of
plots into files is also possible. See the “plot-into-file-example.nlogo” in the examples folder.
Load and Save data from/into file(s)
It’s possible to load and save data from file directly in R. This code snippet illustrates:
r:eval "dataname <- read.table('')" ; read file
r:eval "write.table(dataname, file='')" ; write file
Data.frame with vector in cells
Normally, a data.frame cell contains only a single value. Each column is represented as a vector and if you would put a
vector of vectors to a data.frame, it would be splitted into several columns. With the R-Extension it is possible to put a vector
into a data.frame cell, when you assign a NetLogo List to a column which contains nested NetLogo Lists for each row. If you
want, for example, to use write.table on this data.frame, you have to mark this column as class="AsIs" . You can do this by
using the I(x)-function.
Example: If the column of interest has the name “col1” of the data.frame “df1” you could executer:eval "df1$col1 ')".
Load a Package
It’s also possible to load R packages viar:eval "library()" .
When you compile your code containing extensions [r] you will create a new R workspace. Until you reload the extension,
open a new model or submit the primitive [r:clear](#rclear), all R variables assigned in this session will be available like
you would use R from the command line or in the R Console.
Interactive Shell
You can open an Interactive R Shell via r:interactiveShell. This shell is a port to the underlaying R instance. This shell
works on the global environment (see Environments in the R Extension below) while the extension itself work on a custom
local environment. But there is one automatic variable “nl.env” in the global environment, which is a reference to the local
environment of the extension. Don’t delete this variable!
You can access a variable created by the extension via get("",nl.env), for example myvar ,,envir=.GlobalEnv). If you work with the Interactive Shell, see the notes at the top of the output text
area after opening the shell.
Type help(environment) in an R shell to learn more about environments.
You can/should clear (i.e. remove all variable and free memory) the local environment via[r:clearLocal](#rclearLocal). If
you want to clear also the global environment (the whole workspace), call [r:clear](#rclear).
Memory
With the R-Extension you can load R into the process of NetLogo. Because of the architecture of R, both software share one
system process and therefore the memory given to NetLogo.
In some circumstances it can happen that you receive an out of memory error due to Java’s heap space. You can increase
the heap space before starting NetLogo by adapting the -Xmx JVM-parameter (see also the NetLogo manual section on
Windows memory). But on 32-bit systems, this is very limited. Therefore, it is a good idea to use a 64-bit system if you
want/need to use high amount of RAM. You can see the memory usage of R by starting the interactive shell
(r:interactiveShell) and type there: memory.size(max=F) and memory.size(max=T). Furthermore, you can check the memory
limit by typing: memory.limit().
See also:
R manual page for memory.profile
R manual page for object.size
R manual page for memory.size
If you call the garbage collector in the interactive shell by typing gc(), you will get some information about the current
memory usage (see also http://stat.ethz.ch/R-manual/R-patched/library/base/html/gc.html).
If you type gc(nl.env) you will see the percentage of memory used for cons cells and vectors.
Don’t forget to call the r:gc primitive after removing an R variable and don’t forget to remove R variable you don’t need
anymore! See how the memory usage changes after removing variable and calling r:gc.
If you use too much memory, it can happen, that NetLogo will close abruptly. In such a case, check if there is a way to
reduce the memory used. If not, try to switch over to the Rserve-extension. With the Rserve-Extension both software,
NetLogo and R, run independently. There is, of cause, also a limit of transferable data amount with one request, but it is less
restrictive.
One last note to this topic: Keep in mind that R is a vector-oriented language. Prevent mass calls with single values
whenever possible and replace them by vector operations. This is much faster and more stable.
Headless
Since R-Extension version 1.1 it is possible use the extension when NetLogo is running in headless mode. This is for
example the case, when you run BehaviorSpace experiments from the command line (see here). The difference is, that the
interactiveShell is not initialized/instanciated. You can use the extension as you know it from GUI mode, but it is not
possible to open the interactiveShell (r:interactiveShell) and to set the plot device (r:setPlotDevice). But one additional
things has to be done: You have to call r:stop finally when running NetLogo headless to stop the R engine. Otherwise
NetLogo will not be closed and you will not get back to the command line prompt. When setting up a BehaviorSpace
experiment, there is the option to set final commands. This is a good place to add the r:stop command (see image).
Installing
The R Extension is bundled with NetLogo 6. To use it, you will need a compatible R installation and you may need to
configure the extension.
Installing R
Standard R 3 installations should work (sometimes without configuration). As of NetLogo 6, the following operating system /
R versions were tested:
Mac OS X, R 3.3.2
Windows 10, R 3.3.2
Ubuntu 14.04 (64-bit), R 3.0.2
Once R is installed, you will need to install the rJava package. Certain features of the R extension rely on theJavaGD
package.
To install, start the RGui from your program list, click on the item “Packages” in the menu bar and then on “Install
Package(s)”. Select your favorite server and find “rJava”, as well as “JavaGD” and/or “CommonJavaJars” (both optional) in
the list of packages.
If you prefer using the console, you can install the same packages by running the following commands in the console (and
following the prompts they generate, as appropriate).
install.packages("rJava")
install.packages("JavaGD") # Optional
install.packages("CommonJavaJars") # Optional
Configuring the R extension
If you are using Linux or Mac OS and one of the above R versions, you may not need to perform any further configuration.
An easy way to determine whether you need to configure the extension it to open a new NetLogo model, add extensions [
r ] to the code tab and press “Check.” If you see an error, you need to configure theR extension. The R extension can be
configured by editing the “user.properties” file in a text editor (“user.properties” is located in the r extension directory as part
of the NetLogo installation). The following keys are used to configure the extension:
r.home: Controls which installation of r is used.
jri.home.paths: Controls the path to the jri subdirectory of the rJava library.
r.lib.paths: Controls additional library path(s) with which to initialize R.
Note that you will have to exit NetLogo and restart to see configuration changes take effect, as the configuration file is only
loaded once per NetLogo instance. See below on how to determine the appropriate values for each of these settings.
Configuring the Windows PATH
Windows requires an additional configuration step to make the R extension fully functional. The appropriate directory from
your R installation needs to be added to your PATH. To do this, determine where your R installation is located (here we’ll
use the location C:\Program Files\R\R-), then follow these steps.
1. Open the System Properties dialog. You can type “Environment Variable” into Cortana or navigate there through “Control
Panel” > System > “Advanced system settings”.
2. Click the “Environment variables…” button in the lower right of the dialog.
3. Click the “Path” variable in the lower panel, then click the lower “Edit…” button.
4. Windows 10 allows you to choose “New” and enter a separate path. If you’re using Windows 7, append the value, using a
semicolon to separate it from the entry before.
If you’re using 32-bit NetLogo, enter the location C:\Program Files\R\R-\bin\i386\
If you’re using 64-bit NetLogo, enter the location C:\Program Files\R\R-\bin\x64\
1. Choose OK, and OK again
2. Log out of your user and back in or restart Windows to let the setting take affect.
Note that you will need to update this setting if you wish to upgrade the version of R used by NetLogo.
Notes on editing “user.properties” on Windows
“user.properties” is a newline-delimited file. This means if it is opened in “Notepad” it will look like all the text is on a single
line. For this reason, it is recommended to open first in “WordPad” and resave before editing in Notepad. Alternatively, if you
have a full-featured text editor (like Notepad++, Vim, or Emacs) installed, you can use that to edit the file.
To reiterate a warning given in the “user.properties” file, the directory separator for Windows must be entered in
user.properties as double-backslash (“\”) or single-forward-slash (“/”).
Determining r.home, jri.home.paths, r.lib.paths
is the path to the “R” installation directory which contains the “bin” directory. If you’re having trouble finding this, you
can run R.home(component = "home") in R, or R RHOME on the command line (if R is on your path).
r.home
R.home(component = "home")
# Returns "C:/PROGRA~1/R/R-33~1.2/bin/x64" on Windows.
# Will return other results on other platforms or configurations
jri.home.paths is a list of directories to check for jri. It’s in thejri directory
the jri directory in the rJava package by running the following in R:
under the rJava library installation. You can find
system.file("jri", package = "rJava")
# Returns "C:/Users/username/Documents/R/win-library/3.3/rJava/jri" on Windows.
# Will return other results on other platforms or configurations
is a list of directories that will be set as the rlibPath . Note that the system library (part of the R installation) is
automatically included in the library Path. You can find the directories to include by running the following in R:
r.lib.paths
.libPaths()
# Returns:
# [1] "C:/Users/username/Documents/R/win-library/3.3"
# [2] "C:/Program Files/R/R-3.3.2/library"
Take the path and edit the user.properties file, uncommenting and editing one set ofr.home, jri.home.paths, and
r.lib.paths to match the values obtained in R. When you’re done, the user.properties file should have the following lines
(given the above results):
r.home=C:/PROGRA~1/R/R-33~1.2/bin/x64
jri.home.paths=C:/Users/username/Documents/R/win-library/3.3/rJava/jri
r.lib.paths=C:/Users/username/Documents/R/win-library/3.3
Save user.properties and load a model using the R extension. You should see it start and run properly.
Primitives
r:clear r:clearLocal r:eval r:__evaldirect r:gc r:get r:interactiveShell r:put r:putagent r:putagentdf r:putdataframe
r:putlist r:putnamedlist r:setPlotDevice r:stop
r:clear
r:clear
Clears the R-Workspace. All variables in R will be deleted. It evaluates the R commandrm(list=ls()) and
rm(list=ls(nl.env)). This deletes variables created in global as well as local environment (seeR Environments for details
about environments). It’s always a good idea to add this command to your setup procedure under your “clear-all” call.
;; clear the R workspace
r:clear
r:clearLocal
r:clearLocal
It clears the local R environment, which is used by the extension. All variables which have been created in the local
environment will be deleted. It evaluates the R command rm(list=ls(nl.env)). See R Environments for details about
environments. See r:clear for deleting all variables, i.e. the globals as well.
;; delete the local variables
r:clearLocal
r:eval
r:eval R-command
It evaluates the submitted R command. The R command shouldn’t return a value.
;; creates a new vector in R with a sequence from 1 to 10
r:eval "x <- seq(1,10)"
show r:get "x"
r:__evaldirect
r:__evaldirect R-command
Evaluates the submitted R command in the global environment (not in the local environment liker:eval does) and without a
check (not using try-function internally). This can be necessary for some R packages, like gglopt2. Please note, that you can
produce name clashes when creating new variables using this primitive. The variable will be created into the global
environment and will not overwrite variable with the same name that have been created into the local environment. If you
request a variable with r:get it will search in the local environment first. Therefore, if there are variables with the same name
in the local and the global environment, it will report the variable from the local environment and not the variable created via
r:__evaldirect.
If there is only a variable with the requested name in the global environment, everything will be fine r:get
will report the value of this variable. If you want to remove a variable created via r:__evaldirect, i.e. in the global
environment, call r:eval "rm(myvar, envir=.GlobalEnv)", replace myvar by the name of your variable. The R command
shouldn’t return a value. This primitive is experimental.
;; creates a new vector in R with a sequence from 1 to 10
r:__evaldirect "x <- seq(1,10)"
show r:get "x"
r:gc
r:gc
Calls the garbage collector of Java (i.e. the R-Extension) and R. Call this primitive after removing an R variable to free the
memory.
;; create a variable
r:eval "x <- 1:10"
;; remove the variable
r:eval "rm(x)"
;; call the garbage collector
r:gc
r:get
r:get R-command
Reports the return value of the submitted R command. Return type could be a String, Number, Boolean, NetLogo List or a
NetLogo List of Lists.
R lists will be converted into a NetLogo List. If the R list itself contains further lists, it will be converted into a NetLogo List
with nested NetLogo lists. Lists containing values of different data types are also supported (e.g. mixed Strings, Numbers
and Booleans/Logicals).
Data.frames will be converted into a NetLogo List with nested List for each column, but the column names will be lost (same
for named R lists).
R matrices can be received, but they are converted into one NetLogo list. NULL and NA values are not converted and will
throw an error, because NetLogo has no corresponding value.
;; returns a list with 10 variables
show r:get "rnorm(10)"
r:interactiveShell
r:interactiveShell
Opens a window with two textareas. The upper one is the R output stream and in the lower one you can type R commands.
This is the access to the underlaying R session. You can type multi-line commands. To submit commands press Ctrl+Enter.
With “PageUp” and “PageDown” in the input area you can browse through the histroy of submitted commands. With rightmouseclick context menu, you can save and load an RHistory (interchangeable with R terminal and other R GUIs).
Please note, that the Interactive Shell works on the global environment, while commands submitted from NetLogo lives in an
local environment. A reference to this local environment is automatically added to the global environment (named nl.env,
please do not delete this variable. With a call of r:clear you can restore it but this will empty your workspace). You can use
this to have access to variables which you have created from NetLogo by get("",nl.env). To copy for
example an variable with the name var1 from the local environment to the global environment, typevar n ]
rnd:weighted-n-of-list-with-repeats 100 candidates [ [w] -> w ]
n-values 100 [ rnd:weighted-one-of-list candidates [ [w] -> w ] ]
…the line using rnd:weighted-n-of-list-with-repeats will likely run 100 times faster than the
line using a combination of n-values and rnd:weighted-one-of-list. This is because
rnd:weighted-n-of-list-with-repeats only initializes the algorithm once and rnd:weightedone-of does it each time it is called.
(Note that composing n-values with rnd:weighted-one-of-list does not preserve the order of
the original candidate list, while rnd:weighted-n-of-list-with-repeats does.)
Things are a bit more complicated if you are choosingwithout repeats, however. In this case,
the algorithm may have to discard some picks because the candidates have already been
selected. When this starts happening too often (maybe because some weights are much
bigger than others), the extension re-initializes the algorithm with the already-picked
candidates excluded. This should not happen too often, however, so while picking without
repeats has an upper bound of O(m * n) in theory, it should usually not be much more than
O(m + n) in practice.
The previous remarks apply to agentset primitives as much as they apply to list primitives.
Primitives
AgentSet Primitives
rnd:weighted-one-of rnd:weighted-n-of rnd:weighted-n-of-with-repeats
List Primitives
rnd:weighted-one-of-list rnd:weighted-n-of-list rnd:weighted-n-of-list-with-repeats
rnd:weighted-one-of
rnd:weighted-one-of agentset reporter
Reports a random agent from agentset.
The probability of each agent being picked is proportional to the weight given by thereporter
for that agent. The weights must not be negative.
If the agentset is empty, it reports nobody.
Here is a full rewrite of the Lottery Example model using the rnd:weighted-one-of primitive:
extensions [ rnd ]
to setup
clear-all
; create a turtle on every fifth patch
ask patches with [ pxcor mod 5 = 0 and pycor mod 5 = 0 ] [
sprout 1 [
set size 2 + random 6 ; vary the size of the turtles
set label 0
; start them out with no wins
set color color - 2
; make turtles darker so the labels stand out
]
]
reset-ticks
end
to go
ask rnd:weighted-one-of turtles [ size ] [
set label label + 1
]
tick
end
rnd:weighted-n-of
rnd:weighted-n-of size agentset [ reporter ]
Reports an agentset of the given size randomly chosen from the agentset, with no repeats.
The probability of each agent being picked is proportional to the weight given by thereporter
for that agent. The weights must be non-negative numbers.
It is an error for size to be greater than the size of theagentset.
If, at some point during the selection, there remains only candidates with a weight of0.0, they
all have an equal probability of getting picked.
rnd:weighted-n-of-with-repeats
rnd:weighted-n-of-with-repeats size agentset [ reporter ]
Reports a list of the given size randomly chosen from the agentset, with repeats. (Why a list
instead of an agentset? Because an agentset cannot contain the same agent more than
once.)
The probability of each agent being picked is proportional to the weight given by thereporter
for that agent. The weights must be non-negative numbers.
It is not an error for size to be greater than the size of theagentset, but there has to be at
least one candidate.
If, at some point during the selection, there remains only candidates with a weight of0.0, they
all have an equal probability of getting picked.
If all weights are 0.0, each candidate has an equal probability of being picked.
rnd:weighted-one-of-list
rnd:weighted-one-of-list list anonymous-reporter
Reports a random item from list.
The probability of each item being picked is proportional to the weight given by theanonymousreporter for that item. The weights must not be negative. The first argument passed to the
anonymous procedure refers to the list item. (See the Anonymous Procedures section of the
Programming Guide for more details.)
It is an error for the list to be empty.
A common way to use the primitive is to have a list of lists, where the first item of each sublist
is the thing you want to choose and the second item is the weight. Here is a short example:
let pairs [ [ "A" 0.2 ] [ "B" 0.8 ] ]
repeat 25 [
; report the first item of the pair selected using
; the second item (i.e., `last p`) as the weight
type first rnd:weighted-one-of-list pairs [ [p] -> last p ]
]
This should print B roughly four times more often than it printsA.
If you happen to have your items and your weights in two separate lists, you can combine
them into pairs by using a combination of map and list:
let items [ "A" "B" "C" ]
let weights [ 0.1 0.2 0.7 ]
let pairs (map list items weights)
Since we apply map to both the items list and the weights list, the parentheses are needed in
(map list items weights). We also use the concise anonymous procedure syntax (see the
programming guide) to pass list as the reporter for map. The same thing could have been
written (map [ [a b] -> list a b ] items weights) .
rnd:weighted-n-of-list
rnd:weighted-n-of-list size list anonymous-reporter
Reports a list of the given size randomly chosen from the list of candidates, with no repeats.
The probability of each item being picked is proportional to the weight given by theanonymousreporter for that item. The weights must not be negative. The first argument passed to the
anonymous procedure refers to the list item. (See the Anonymous Procedures section of the
Programming Guide for more details.)
It is an error for size to be greater than the size of thelist of candidates .
If, at some point during the selection, there remains only candidates with a weight of0.0, they
all have an equal probability of getting picked.
The items in the resulting list appear in the same order that they appeared in the list of
candidates. (If you want them in random order, use shuffle on the result).
Example:
let candidates n-values 8 [ [n] -> 2 ^ (n + 1) ] ; make a list with the powers of two
print rnd:weighted-n-of-list 4 candidates [ [w] -> w ]
This should print a list of four numbers, where the bigger numbers (32, 64, 128, 256) have a
much better chance to show up than the smaller ones (2, 4, 8, 16).
rnd:weighted-n-of-list-with-repeats
rnd:weighted-n-of-list-with-repeats size list anonymous-reporter
Reports a list of the given size randomly chosen from the list of candidates, with repeats.
The probability of each item being picked is proportional to the weight given by theanonymousreporter for that item. The weights must not be negative. The first argument passed to the
anonymous procedure refers to the list item. (See the Anonymous Procedures section of the
Programming Guide for more details.)
It is not an error for size to be greater than the size of thelist of candidates, but there has to
be at least one candidate.
If, at some point during the selection, there remains only candidates with a weight of0.0, they
all have an equal probability of getting picked.
If all weights are 0.0, each candidate has an equal probability of being picked.
The items in the resulting list appear in the same order that they appeared in the list of
candidates. (If you want them in random order, use shuffle on the result).
Example:
let pairs [ [ "A" 0.2 ] [ "B" 0.8 ] ]
print map first rnd:weighted-n-of-list-with-repeats 25 pairs [ [p] -> last p ]
This should print a list of 25 As and Bs, with roughly four times as manyBs than As.
NetLogo Sound Extension
Using
The Sound Extension lets NetLogo models make two kinds of sounds: MIDI sounds and
playback of pre-recorded sound files.
The Java APIs used are javax.sound.midi and java.applet.AudioClip.
How to Use
The sound extension comes preinstalled. To use the extension in your model, add this at
the top of your Code tab:
extensions [sound]
If your model already uses other extensions, then it already has anextensions line in it, so
just add sound to the list.
For more information on using NetLogo extensions, see theExtensions Guide
For examples that use the sound extension, see the Sound section under Code Examples
in the NetLogo Models Library.
MIDI support
The MIDI part of the extension simulates a 128-key electronic keyboard with47 drums and
128 melodic instruments, as provided by General MIDI Level 1 specification.
It supports 15 polyphonic instrument channels and a single percussion channel. Using
more than 15 different melodic instruments simultaneously in a model will cause some
sounds to be lost or cut off.
The pitch of a melodic instrument is specified by a key number. The keys on the keyboard
are numbered consecutively from 0 to 127, where 0 is the left-most key. Middle C is key
number 60.
The loudness of an instrument is specified by a velocity, which represents the force with
which the keyboard key is depressed. Velocity ranges from 0 to 127, where 64 is the
standard velocity. A higher velocity results in a louder sound.
Primitives
sound:drums sound:instruments sound:play-drum sound:play-note sound:play-note-later
sound:drums
sound:drums
Reports a list of the names of the 47 drums for use with sound:play-drum.
sound:instruments
sound:instruments
Reports a list of the names of the 128 instruments for use with sound:play-note,
sound:play-note-later, sound:start-note and sound:stop-note.
sound:play-drum
sound:play-drum drum velocity
Plays a drum.
Example:
sound:play-drum "ACOUSTIC SNARE" 64
sound:play-note
sound:play-note instrument keynumber velocity duration
Plays a note for a specified duration, in seconds. The agent does not wait for the note to
finish before continuing to next command.
;; play a trumpet at middle C for two seconds
sound:play-note "TRUMPET" 60 64 2
sound:play-note-later
sound:play-note-later delay instrument keynumber velocity duration
Waits for the specified delay before playing the note for a specified duration, in seconds.
The agent does not wait for the note to finish before continuing to next command.
Example:
;; in one second, play a trumpet at middle C for two seconds
sound:play-note-later 1 "TRUMPET" 60 64 2
Drum Names
35.
36.
37.
38.
39.
40.
41.
42.
43.
44.
Acoustic Bass Drum
Bass Drum 1
Side Stick
Acoustic Snare
Hand Clap
Electric Snare
Low Floor Tom
Closed Hi Hat
Hi Floor Tom
Pedal Hi Hat
59.
60.
61.
62.
63.
64.
65.
66.
67.
68.
Ride Cymbal 2
Hi Bongo
Low Bongo
Mute Hi Conga
Open Hi Conga
Low Conga
Hi Timbale
Low Timbale
Hi Agogo
Low Agogo
45.
47.
47.
48.
49.
50.
51.
52.
53.
54.
55.
56.
57.
58.
Low Tom
Open Hi Hat
Low Mid Tom
Hi Mid Tom
Crash Cymbal 1
Hi Tom
Ride Cymbal 1
Chinese Cymbal
Ride Bell
Tambourine
Splash Cymbal
Cowbell
Crash Cymbal 2
Vibraslap
69.
70.
71.
72.
73.
74.
75.
76.
77.
78.
79.
80.
81.
Cabasa
Maracas
Short Whistle
Long Whistle
Short Guiro
Long Guiro
Claves
Hi Wood Block
Low Wood Block
Mute Cuica
Open Cuica
Mute Triangle
Open Triangle
Instrument Names
*Piano*
1. Acoustic Grand Piano
2. Bright Acoustic Piano
3. Electric Grand Piano
4. Honky-tonk Piano
5. Electric Piano 1
6. Electric Piano 2
7. Harpsichord
8. Clavi
*Reed*
65. Soprano Sax
66. Alto Sax
67. Tenor Sax
68. Baritone Sax
69. Oboe
70. English Horn
71. Bassoon
72. Clarinet
*Chromatic Percussion*
9. Celesta
10. Glockenspiel
11. Music Box
12. Vibraphone
13. Marimba
14. Xylophone
15. Tubular Bells
16. Dulcimer
*Pipe*
73. Piccolo
74. Flute
75. Recorder
76. Pan Flute
77. Blown Bottle
78. Shakuhachi
79. Whistle
80. Ocarina
*Organ*
17. Drawbar Organ
18. Percussive Organ
19. Rock Organ
20. Church Organ
21. Reed Organ
22. Accordion
23. Harmonica
24. Tango Accordion
*Synth Lead*
81. Square Wave
82. Sawtooth Wave
83. Calliope
84. Chiff
85. Charang
86. Voice
87. Fifths
88. Bass and Lead
*Guitar*
25. Nylon String Guitar
26. Steel Acoustic Guitar
27. Jazz Electric Guitar
28. Clean Electric Guitar
29. Muted Electric Guitar
30. Overdriven Guitar
31. Distortion Guitar
32. Guitar harmonics
*Synth Pad*
89. New Age
90. Warm
91. Polysynth
92. Choir
93. Bowed
94. Metal
95. Halo
96. Sweep
*Bass*
33. Acoustic Bass
34. Fingered Electric Bass
35. Picked Electric Bass
36. Fretless Bass
37. Slap Bass 1
38. Slap Bass 2
39. Synth Bass 1
40. Synth Bass 2
*Synth Effects*
97. Rain
98. Soundtrack
99. Crystal
100. Atmosphere
101. Brightness
102. Goblins
103. Echoes
104. Sci-fi
*Strings*
41. Violin
42. Viola
43. Cello
44. Contrabass
45. Tremolo Strings
47. Pizzicato Strings
*Ethnic*
105. Sitar
106. Banjo
107. Shamisen
108. Koto
109. Kalimba
110. Bag pipe
47. Orchestral Harp
48. Timpani
111. Fiddle
112. Shanai
*Ensemble*
49. String Ensemble 1
50. String Ensemble 2
51. Synth Strings 1
52. Synth Strings 2
53. Choir Aahs
54. Voice Oohs
55. Synth Voice
56. Orchestra Hit
*Percussive*
113. Tinkle Bell
114. Agogo
115. Steel Drums
116. Woodblock
117. Taiko Drum
118. Melodic Tom
119. Synth Drum
120. Reverse Cymbal
*Brass*
57. Trumpet
58. Trombone
59. Tuba
60. Muted Trumpet
61. French Horn
62. Brass Section
63. Synth Brass 1
64. Synth Brass 2
*Sound Effects*
121. Guitar Fret Noise
122. Breath Noise
123. Seashore
124. Bird Tweet
125. Telephone Ring
126. Helicopter
127. Applause
128. Gunshot
NetLogo Table Extension
Using
The table extension is pre-installed in NetLogo.
To use the table extension in your model, add a line to the top of your Code tab:
extensions [table]
If your model already uses other extensions, then it already has anextensions line in it, so
just add table to the list.
For more information on using NetLogo extensions, see theExtensions Guide
When to Use
In general, anything you can do with an table in NetLogo, you could also just use a list for.
But you may want to consider using an table instead for speed reasons. Lists and tables
have different performance characteristics, so you may be able to make your model run
faster by selecting the appropriate data structure.
Tables are useful when you need to do associate values with other values. For example,
you might make a table of words and their definitions. Then you can look up the definition
of any word. Here, the words are the "keys". You can easily retrieve the value for any key
in the table, but not vice versa.
Unlike NetLogo’s lists and strings, tables are “mutable”. That means that you can actually
modify them directly, rather than constructing an altered copy as with lists. If the table is
used in more than one place in your code, any changes you make will show up
everywhere. It’s tricky to write code involving mutable structures and it’s easy to make
subtle errors or get surprising results, so we suggest sticking with lists and strings unless
you’re certain you want and need mutability.
Example
let dict table:make
table:put dict "turtle" "cute"
table:put dict "bunny" "cutest"
print dict
=> {{table: "turtle" -> "cute", "bunny" -> "cutest" }}
print table:length dict
=> 2
print table:get dict "turtle"
=> "cute"
print table:get dict "leopard"
=> (error)
print table:keys dict
=> ["turtle" "bunny"]
Primitives
table:clear table:counts table:from-list table:get table:has-key? table:keys
table:length table:make table:put table:remove table:to-list table:values
table:clear
table:clear table
Removes all key-value pairs from table.
table:counts
table:counts list
Counts the occurrences of each element of the given list and reports the counts in a table.
table:from-list
table:from-list list
Reports a new table with the contents oflist. list must be a list of two element lists, or
pairs. The first element in the pair is the key and the second element is the value.
table:get
table:get table key
Reports the value that key is mapped to in the table. Causes an error if there is no entry
for the key.
table:has-key?
table:has-key? table key
Reports true if key has an entry in table.
table:keys
table:keys table
Reports a list of all the keys in table, in the same order the keys were inserted.
table:length
table:length table
Reports the number of entries in table.
table:make
table:make
Reports a new, empty table.
table:put
table:put table key value
Maps key to value in table. If an entry already exists in the table for the given key, it is
replaced.
table:remove
table:remove table key
Removes the mapping in table for key.
table:to-list
table:to-list table
Reports a list with the content of table. The list will be a list of two element lists, or pairs.
The first element in the pair is the key and the second element is the value. The keys
appear in the same order they were inserted.
table:values
table:values table
Reports a list with the entries of table. The entries will appear in the same order they were
inserted, with duplicates included.
NetLogo Vid Extension
Concepts
Video Source
The vid extension has a built-in concept of a video source. At the moment, the only video sources
available are movies in the directory the model lives in and cameras attached to the computer. The
vid extension opens a new video source with thevid:-open and vid:-select.
These primitives change the source to the selected source. If a source is already open, it closes it
before opening a new one.
Source Lifecycle
Movie sources are “stopped” after being created by vid:movie-select or vid:movie-open. Camera
sources start off as “playing” after being created by vid:camera-select or vid:camera-open. If a
source is in status “stopped” it can be started with vid:start. Conversely, if the source is “playing” it
can be stopped with vid:stop. When a source is “stopped”, each call to vid:capture-image will
return the same image.
Video Recorder
The vid extension also has the concept of a recording, a series of frames which can be sewn into
an “mp4” movie. The recorder status can be queried using vid:recorder-status. The recorder
status is “inactive” until started with vid:start-recorder, which sets it to “recording”. While the
recorder is “recording” the vid:record-view, vid:record-interface, and vid:record-source can be
used to save frames to the recording. You can choose to save the recording while recording using
vid:save-recording which saves the movie to the specified file and reset the recording status to
“inactive”. If you would prefer to throw away the recorded frames without saving, use vid:resetrecorder.
Primitives
vid:camera-names vid:camera-open vid:camera-select vid:movie-select vid:movie-open vid:movieopen-remote vid:close vid:start vid:stop vid:status vid:capture-image vid:set-time vid:showplayer vid:hide-player vid:record-view vid:record-interface vid:record-source vid:recorderstatus vid:start-recorder vid:save-recording
vid:camera-names
vid:camera-names
Provides a list of all available cameras.
Example:
vid:camera-names => []
vid:camera-names => ["Mac Camera"]
vid:camera-names => ["Logitech Camera"]
vid:camera-open
vid:camera-open
Opens the named camera as a video source. If no name is provided, opens the first camera that
would be listed by camera-names .
Example:
vid:camera-open ; opens first camera
(vid:camera-open "Logitech Camera")
Errors:
Message "vid: no cameras found" : no cameras are available.
Message "vid: camera "\" not found" : if the named camera is not available.
vid:camera-select
vid:camera-select
Prompts the user to select a camera as video source. This command does not error if the user
cancels. Use vid:status to see if a user selected a camera.
Example:
vid:camera-select
Errors:
Message “vid: no cameras found”: no cameras are available.
vid:movie-select
vid:movie-select
Prompts the user to select a movie to use as a video source. The formats supported are those
supported by JavaFX2. This command does not error if the user cancels. Usevid:status to see if
the user selected a movie.
Example:
vid:movie-select
Errors:
Message "vid: format not supported" : the user selected a movie with an unsupported format.
vid:movie-open
vid:movie-open filename
Opens a video from the file system. If the provided path is not absolute the extension searches for
the given path relative to the current model directory. If the provided path is absolute the extension
opens the file.
Example:
vid:movie-open "foo.mp4"
; Opens foo.mp4 in the directory containing the model
vid:movie-open user-file
; Opens a dialog for the user to select a movie
vid:movie-open "/tmp/foo.mp4" ; Opens a movie from the "/tmp" directory
Errors:
Message "vid: no movie found" : the movie could not be found.
Message "vid: format not supported" : the user selected a movie with an unsupported format.
vid:movie-open-remote
vid:movie-open-remote url
Opens a remote video from a website or ftp server.
Example:
vid:movie-open-remote "http://example.org/foo.mp4"
Errors:
Message "vid: no movie found" : The specified URL could not be loaded or errored while
loading.
Message "vid: format not supported" : The file type of the remote movie is not supported.
Message "vid: protocol not supported": The movie was at an unsupported URL protocol.
Supported protocols are ftp and http.
vid:close
vid:close
Closes the currently selected video source. Has no effect if there is no active video source.
Example:
vid:close
vid:start
vid:start
Starts the selected video source. A video source must have been selected before callingvid:start.
Example:
vid:start
Errors:
Message "vid: no selected source" : There is no currently selected video source. Select a
source with vid:movie-open, vid:movie-select, vid:camera-open, or vid:camera-select .
vid:stop
vid:stop
Stops the currently running video source.
Example:
vid:stop
vid:status
vid:status
Reports the current status of an active video. Note that after callingvid:movie-open or vid:movieselect the status will be set to “stopped”, while after callingvid:camera-open or vid:camera-select
the status will be “playing”.
Example:
vid:status
; => "inactive"
vid:movie-open "foobar.mp4"
vid:status
; => "stopped"
vid:movie-start
vid:status
; => "playing"
vid:capture-image
vid:capture-image width height
Captures an image from the currently selected active source.
If width and height are not specified, the image is captured at the current source resolution.
Example:
extensions [ vid bitmap ]
to capture
; capture an image if a video source is open,
; have the user select a camera if no video source found
carefully [
; when camera open, take an image
let image vid:capture-image ; returns image suitable for use with bitmap extension
bitmap:copy-to-drawing image 0 0
] [
if error-message = "Extension exception: vid: no selected source" [
vid:camera-select
vid:start
let image vid:capture-image
bitmap:copy-to-drawing image 0 0
]
]
end
If you want to capture images at a different resolution, simply replacevid:capture-image with, e.g.,
(vid:capture-image 640 480).
Errors:
Message "vid: no selected source" : There is no currently selected video source. Select a
source with vid:movie-open, vid:movie-select, vid:camera-open, or vid:camera-select .
Message "vid: invalid dimensions" : The selected dimensions are invalid (one of the
dimensions is zero or negative).
vid:set-time
vid:set-time seconds
Sets the time of the current video source to*seconds*. This has no effect when the current video
source is a camera.
Example:
vid:set-time 100
Errors:
Message "vid: no selected source" : There is no currently selected video source. Select a
source with vid:movie-open, vid:movie-select, vid:camera-open, or vid:camera-select .
Message "vid: invalid time" : The currently active video does not contain the specified second.
The second may be negative, or greater than the length of the video.
vid:show-player
vid:show-player width height
Shows a player in a separate window. If there is no video source, the window will be an empty black
frame. If there is an active video source, it will be displayed in the window with the specified width
and height. If there is a playing video source, it will be displayed in the window at its specified width
and height. If width and height are omitted, the video will be displayed in its native resolution.
Example with native resolution:
vid:show-player
Example with custom resolution:
(vid:show-player 640 480)
Errors:
Message "vid: invalid dimensions" : The selected dimensions are invalid (one of the
dimensions is zero or negative).
vid:hide-player
vid:hide-player
Hides the player if open. Does nothing if there is no player window.
Example:
vid:hide-player
vid:record-view
vid:record-view
Records the current image shown in the NetLogo view to the active recording.
Example:
vid:record-view
Errors:
Message "vid: recorder not started": The recorder has not been started. Start the recorder
with vid:start-recorder.
vid:record-interface
vid:record-interface
Records the NetLogo interface view to the active recording.
Example:
vid:record-interface
Errors:
Message "vid: recorder not started": The recorder has not been started. Start the recorder
with vid:start-recorder.
Message "vid: export interface not supported" : The calling NetLogo version does not support
interface exports. This will occur when running NetLogo headlessly.
vid:record-source
vid:record-source
Records a frame to the active recording from the currently active source.
Example:
vid:record-source
Errors:
Message "vid: recorder not started": The recorder has not been started. Start the recorder
with vid:start-recorder.
Message "vid: no selected source" : There is no currently selected video source. Select a
source with vid:movie-open, vid:movie-select, vid:camera-open, or vid:camera-select .
vid:recorder-status
vid:recorder-status
Reports the current status of the recorder. Initially and after the recorder is saved (viavid:saverecording) or reset (via vid:reset-recorder) the recorder status is “inactive”. After calling
vid:start-recorder the status will be “recording”.
Example:
vid:recorder-status ; => "inactive"
vid:start-recorder
vid:recorder-status ; => "recording"
vid:reset-recorder
vid:recorder-status ; => "inactive"
vid:start-recorder
vid:start-recorder
Starts the recorder. If the recorder is already running this will cause an error to be raised. If desired,
a recording width and height can be supplied. If width and height are not supplied, they will be
determined from the first frame recorded.
Example:
vid:start-recorder
(vid:start-recorder 640 480)
Errors:
Message "vid: recorder already started": The recorder has already been started. The existing
recording should be saved or reset before starting the recording.
Message "vid: invalid dimensions" : The selected dimensions are invalid (one of the
dimensions is zero or negative).
vid:save-recording
vid:save-recording filename
Saves the recording to the specified path. If the recorder is not running this will cause an error to be
raised. Note that at present the recording will always be saved in the “mp4” format. If the supplied
filename does not end in “.mp4”, the “.mp4” suffix will be added. Note that vid:save-recording will
overwrite existing files of the same name. vid:save-recording will error if the recorder has not been
started or if the file cannot be written since the containing directory does not exist.
Example:
vid:save-recording "foo.mp4"
; Saves to foo.mp4 in the directory containing the model
vid:save-recording user-new-file ; Opens a dialog for the user to select a save path
vid:save-recording "/tmp/foo.mp4" ; Saves the recording to the "/tmp" directory
Errors:
Message "vid: recorder not started": The recorder has not been started. Start the recorder
with vid:start-recorder.
Message "vid: no such directory" : The directory containing the specified save file does not
exist.
Message "vid: no frames recorded" : You tried to save a recording with no frames recorded.
Check that you are recording properly or use vid:reset-recording to to change the recording
format without saving.
NetLogo View2.5d Extension
The View2.5D extension offers visualization for Patch and Turtle reporters, in real time, in a
simulation’s context.
How to Use
The view2.5d extension is pre-installed in NetLogo.
To use the view2.5d extension in your model, add a line to the top of your Code tab:
extensions [view2.5d]
If your model already uses other extensions, then it already has anextensions line in it, so just add
view2.5d to the list.
For more information on using NetLogo extensions, see theExtensions Guide
Incorporating Into Models
open a window using either the view2.5d:patch-view or view2.5d:turtle-view commands (it can be a
good idea to put these in your ‘SETUP’ procedure or a separate button).
update your window’s view using one of the update commands (put these in your ‘GO’ procedure).
See the View2.5d Code Examples in the NetLogo models library.
Feedback
Send comments, bugs, or other feedback toCCL Feedback and/or Corey Brady.
Primitives
view2.5d:patch-view view2.5d:decorate-patch-view view2.5d:undecorate-patch-view view2.5d:turtleview view2.5d:update-all-patch-views view2.5d:update-patch-view view2.5d:update-turtle-view
view2.5d:get-z-scale view2.5d:set-z-scale view2.5d:set-turtle-stem-thickness view2.5d:getobserver-angles view2.5d:set-observer-angles view2.5d:get-observer-xy-focus view2.5d:set-observerxy-focus view2.5d:get-observer-distance view2.5d:set-observer-distance view2.5d:remove-patch-view
view2.5d:remove-turtle-view view2.5d:remove-all-patch-views view2.5d:remove-all-turtle-views
view2.5d:count-windows
view2.5d:patch-view
view2.5d:patch-view Title Reporter
This command must be called from the Observer context. (Attempting to call from another context
causes an error) The Title is a string, which will be used to label the new Window and to call for
subsequent updates and modifications. Specification of the Reporter uses the NetLogo anonymous
procedure syntax, from the Observer perspective.
Example:
view2.5d:patch-view "Test" [ [the-turtle] -> [pxcor] of the-turtle]
view2.5d:decorate-patch-view
view2.5d:decorate-patch-view Title
This command must be called from the Observer context. (Attempting to call from another context
causes an error) The Title is a string, the label of an existing Patch View Window. Effect: draws the
turtles of the model at their current location, on top of the Patch view display
NOTE: only has an effect in the “structures” patch view (in the others, the patch value is
inclined based on neighbors & gradient)
NOTE: for negative patch values, the turtle shapes are drawn below (orbit underneath to
see them)
Example:
view2.5d:decorate-patch-view "Test"
view2.5d:undecorate-patch-view
view2.5d:undecorate-patch-view Title
This command must be called from the Observer context. (Attempting to call from another context
causes an error)
The Title is a string, the label of an existing Patch View Window. Effect: STOPS drawing the turtles of
the model at their current location, on top of the Patch view display
Example:
view2.5d:undecorate-patch-view "Test"
view2.5d:turtle-view
view2.5d:turtle-view Title Agents Reporter
This command must be called from the Observer context. (Attempting to call from another context
causes an error) The Title is a string, which will be used to label the new Window and to call for
subsequent updates. The turtle-set is any selector for turtles. Specification of the Reporter uses the
NetLogo task syntax, from the Observer perspective.
Example:
view2.5d:turtle-view "Test" turtles with [color = red] [[energy] of ?1]
; This would create a new 2.5d window, plotting the ENERGY value of all turtles that are red.
view2.5d:update-all-patch-views
view2.5d:update-all-patch-views
This command must be called from the Observer context. Updates all existing patch-view windows
according to the latest values.
view2.5d:update-patch-view
view2.5d:update-patch-view Title
This command must be called from the Observer context. Updates only the patch-view window with the
specified title (if any).
view2.5d:update-turtle-view
view2.5d:update-turtle-view Title Agents
This command must be called from the Observer context. Updates only the turtle-view window with the
specified title (if any). The turtle-set selector must be supplied to refresh the set of turtles.
view2.5d:get-z-scale
view2.5d:get-z-scale title
This reporter must be called from the Observer context. Returns the current z-scale of the turtle-view or
patch-view window with the specified title (if any).
view2.5d:set-z-scale
view2.5d:set-z-scale Title new-z-scale
This command must be called from the Observer context. Updates only the turtle-view or patch-view
window with the specified title (if any). The view is now displayed with the new z-scale.
view2.5d:set-turtle-stem-thickness
view2.5d:set-turtle-stem-thickness Title thickness
This command must be called from the Observer context. Updates only the turtle-view window with the
specified title (if any). Turtles are now drawn with “pins” or “stems” that have the specified thickness
(instead of the hairline default)
view2.5d:get-observer-angles
view2.5d:get-observer-angles Title
This reporter must be called from the Observer context. Returns a list reflecting the observer’s angular
perspective { heading pitch } (the place on an imaginary sphere at the zoom distance is updated to
obey heading & pitch given)
view2.5d:set-observer-angles
view2.5d:set-observer-angles Title heading pitch
This command must be called from the Observer context. Updates only the turtle-view window with the
specified title (if any). Sets the observer’s angular perspective (the place on an imaginary sphere at the
zoom distance is updated to obey heading & pitch given)
view2.5d:get-observer-xy-focus
view2.5d:get-observer-xy-focus Title
This reporter must be called from the Observer context. Returns a list reflecting the x and y coordinates
the observer is “looking at” in the patch plane.
view2.5d:set-observer-xy-focus
view2.5d:set-observer-xy-focus Title number ycor
This command must be called from the Observer context. Updates only the turtle-view window with the
specified title (if any). Sets the x and y coordinates the observer that is “looking at” in the patch plane.
view2.5d:get-observer-distance
view2.5d:get-observer-distance Title
This reporter must be called from the Observer context. Returns the observer’s distance from its “focus
point”
view2.5d:set-observer-distance
view2.5d:set-observer-distance Title new-distance
This command must be called from the Observer context. Updates only the turtle-view window with the
specified title (if any). Sets the observer’s distance from its “focus point”
view2.5d:remove-patch-view
view2.5d:remove-patch-view Title
This command closes and removes the specified patch view programmatically (equivalent to closing
the window manually).
view2.5d:remove-turtle-view
view2.5d:remove-turtle-view Title
This command closes and removes the specified turtle view programmatically (equivalent to closing
the window manually).
view2.5d:remove-all-patch-views
view2.5d:remove-all-patch-views
This command closes and removes all patch views programmatically (equivalent to closing the
windows manually).
view2.5d:remove-all-turtle-views
view2.5d:remove-all-turtle-views
This command closes and removes all turtle views programmatically (equivalent to closing the
windows manually).
view2.5d:count-windows
view2.5d:count-windows
This reporter returns the number of turtle and patch views that are currently active.
FAQ (Frequently Asked Questions)
Feedback from users is very valuable to us in designing and improving NetLogo. We'd like to
hear from you. (See Contacting Us.)
Questions
General
Why is it called NetLogo?
How do I cite NetLogo or HubNet in a publication?
How do I cite a model from the Models Library in a publication?
Where and when was NetLogo created?
What programming language was NetLogo written in?
What's the difference between StarLogo and NetLogo?
Under what license is NetLogo released? Is the source code available?
Do you offer any workshops or other training opportunities for NetLogo?
Are there any NetLogo textbooks?
Is NetLogo available in other languages besides English?
Is NetLogo compiled or interpreted?
Has anyone built a model of ?
Are NetLogo models runs scientifically reproducible?
Will NetLogo and NetLogo 3D remain separate applications?
Can I run NetLogo on my tablet or phone?
Downloading
Can I have multiple versions of NetLogo installed at the same time?
I'm on a UNIX system and I can't untar the download. Why?
How do I install NetLogo unattended?
Running
Can I run NetLogo from a CD, a network drive, or a USB drive?
Why is NetLogo so much slower when I unplug my Windows laptop?
Why does NetLogo bundle Java?
How come NetLogo won't start up on my Linux machine?
When I try to install NetLogo on Windows, I see "Windows protected your PC"
When I try to start NetLogo on Windows I get an error "The JVM could not be started". Help!
NetLogo won't start on Mac OS Sierra (or later)
NetLogo won't start on Windows or crashes suddenly on Mac OS Sierra
Can I run NetLogo from the command line, without the GUI?
Does NetLogo take advantage of multiple processors/cores?
Can I distribute NetLogo model runs across a cluster or grid of computers?
Is there any way to recover lost work if NetLogo crashes or freezes?
Usage
When I move the speed slider all the way to the right, why does my model seem to stop?
Can I use the mouse to "paint" in the view?
How big can my model be? How many turtles, patches, procedures, buttons, and so on can my
model contain?
Can I use GIS data in NetLogo?
My model runs slowly. How can I speed it up?
Can I have more than one model open at a time?
Can I change the choices in a chooser on the fly?
Can I divide the code for my model up into several files?
Programming
How does the NetLogo language differ from other Logos?
How come my model from an earlier NetLogo doesn't work right?
How do I take the negative of a number?
My turtle moved forward 1, but it's still on the same patch. Why?
How do I keep my turtles on patch centers?
patch-ahead 1 is reporting the same patch my turtle is already standing on. Why?
How do I give my turtles "vision"?
Can agents sense what's in the drawing layer?
I'm getting numbers like 0.10000000004 and 0.799999999999 instead of 0.1 and 0.8. Why?
The documentation says that random-float 1.0 might return 0.0 but will never return 1.0. What if I want
1.0 to be included?
How can I use different patch "neighborhoods" (circular, Von Neumann, Moore, etc.)?
How can I keep two turtles from occupying the same patch?
How can I find out if a turtle is dead?
Does NetLogo have arrays?
Does NetLogo have hash tables or associative arrays?
How can I convert an agentset to a list, or vice versa?
How do I stop foreach?
I'm trying to make a list. Why do I keep getting the error "Expected a constant"?
BehaviorSpace
Why are the rows in my BehaviorSpace table results out of order?
How do I gather data every n ticks?
I'm varying a global variable I declared in the Code tab, but it doesn't work. Why?
Why are some of my results cut off in Excel?
NetLogo 3D
Does NetLogo 3D work with my stereoscopic device?
Extensions
I'm writing an extension. Why does the compiler say it can't find org.nlogo.api?
General
Why is it called NetLogo?
The "Logo" part is because NetLogo is a dialect of the Logo language.
"Net" is meant to evoke the decentralized, interconnected nature of the phenomena you can
model with NetLogo, including network phenomena. It also refers to HubNet, the multiuser
participatory simulation environment included in NetLogo.
How do I cite NetLogo or HubNet in a publication?
If you use or refer to NetLogo, HubNet or a model from the NetLogo models library, we ask
that you cite it as follows:
NetLogo itself: Wilensky, U. 1999. NetLogo. http://ccl.northwestern.edu/netlogo/. Center for
Connected Learning and Computer-Based Modeling, Northwestern University. Evanston, IL.
HubNet: Wilensky, U. & Stroup, W., 1999. HubNet.
http://ccl.northwestern.edu/netlogo/hubnet.html. Center for Connected Learning and
Computer-Based Modeling, Northwestern University. Evanston, IL.
How do I cite a model from the Models Library in a publication?
The correct citation is included in the "Credits and References" section of each model's Info
tab.
Where and when was NetLogo created?
NetLogo was first created in 1999 by Uri Wilensky at the Center for Connected Learning and
Computer-Based Modeling, then at Tufts University in the Boston area. NetLogo grew out of
StarLogoT, which was authored by Wilensky in 1997. In 2000, the CCL moved to
Northwestern University, in the Chicago area. NetLogo 1.0 came out in 2002, 2.0 in 2003, 3.0
in 2005, 4.0 in 2007, 4.1 in 2009, and 5.0 in 2012.
What programming language was NetLogo written in?
NetLogo is written mostly in Scala, with some parts in Java. (Scala code compiles to Java
byte code and is fully interoperable with Java and other JVM languages.)
What's the relationship between StarLogo and NetLogo?
The original StarLogo began at the MIT Media Lab in 1989 and ran on the Connection
Machine. Later versions were developed for Macintosh computers: MacStarLogo (1994, MIT)
and StarLogoT (1997, Tufts).
Today there are two StarLogo descendants under active development: NetLogo (from the
CCL at Northwestern University) and StarLogo TNG (from MIT). NetLogo is the most widely
used agent-based modeling environment in both education and research. StarLogo TNG is
distinguished by its programming interface based on colored blocks.
Under what license is NetLogo released? Is the source code
available?
NetLogo is free, open source software under the GPL (GNU General Public License), version
2, or (at your option) any later version.
Commercial licenses are also available. To inquire about commercial licenses, please contact
Uri Wilensky at uri@northwestern.edu.
The source code is on GitHub, here. Development discussion is on the netlogo-devel group.
The User Manual is published under a Creative Commons Attribution-ShareAlike license (CC
BY-SA 3.0).
Source code for all of the extensions bundled with NetLogo is on GitHub, here. Most of the
extensions are in the public domain (CC0 notice). Other extensions are released under open
source licenses. See each extension's README for details.
The Code Examples in the Models Library are in the public domain (CC0 notice).
The rest of the models in the Models Library are provided under a variety of licenses. Some
are public domain and some are open source, but most are under the Creative Commons
Attribution-ShareAlike license (CC BY-NC-SA), which is not an open source license, though
the models are free for noncommercial distribution and use.
See each model's Info tab to check its particular license.
The models are in a public Git repository here.
Do you offer any workshops or other training opportunities for
NetLogo?
We offer workshops from time to time. If a workshop has been scheduled, we will announce it
on the NetLogo Users Group.
Are there any NetLogo textbooks?
The CCL has published a textbook (written by the author of NetLogo) that gives an
introduction to agent-based modeling methods using NetLogo. It goes step by step with
coding examples how to design, build, revise, and analyze models. And it presents some
advanced techniques.
See www.intro-to-abm.com for more information on that textbook.
See the Textbooks section of our Resources page.
We at the CCL have hoped to write several more NetLogo textbooks. These could be aimed
at different audiences, such as: middle school, high school, undergraduate course in modeling
or complexity, practical guide for interested adults.
Unfortunately, we have not yet been able to find the time to make these happen. If anyone
from the user community would like to collaborate on such a venture, please let us know. We
would welcome it.
Is NetLogo available in other languages besides English?
Volunteers have translated the user manual into Chinese and Czech. The translated versions
are available from the NetLogo web site.
So far, the NetLogo user interface has been localized in English, Spanish, Chinese, Russian,
and Japanese. All five languages are included in the standard download.
We are seeking volunteers to complete and improve these localizations and to translate the
NetLogo software and manual into as many other languages as possible. If you're able to help
in this endeavor, please contact us.
Is NetLogo compiled or interpreted?
Short answer: some of both.
Long answer: NetLogo does include a compiler that generates Java byte code. However, this
compiler does not yet support the entire language, so some parts of user code remain
interpreted. Note that our compiler generates Java byte code, and Java virtual machines have
"just-in-time" compilers that in turn compile Java byte code all the way to native code, so
much user code is ultimately translated to native code.
Has anyone built a model of ?
Try looking at the NetLogo Models Library, the NetLogo Modeling Commons, our Community
Models page, and our list of references to NetLogo in outside works.
You might also ask the question on the NetLogo Users Group and/or search past messages
on the group.
Are NetLogo models runs scientifically reproducible?
Yes. NetLogo's pseudorandom number generator and agent scheduling algorithms are
deterministic, and NetLogo always uses Java's "strict math" library, which gives bit-for-bit
identical results regardless of platform. But keep the following cautions in mind:
If your model uses random numbers, then in order to get reproducible behavior, you
must use the random-seed command to set the random seed in advance, so that your
model will receive the exact same sequence of random numbers every time.
Remember that agentsets are always in random order, so anything you do with
agentsets uses random numbers.
If your model uses the every or wait commands in such a way that affects the outcome
of the model, then you may get different results on different computers, or even on the
same computer, since the model may run at a different speed.
In order to reproduce model runs exactly, you must be using the exact same version of
NetLogo. The details of the agent scheduling mechanism and the random number
generator may change between NetLogo versions, and other changes (bugfixes in the
engine, language changes, and so forth) may also affect the behavior of your model.
(Then again, they may not.)
We have expended every effort to make NetLogo model runs fully reproducible, but of
course this can never truly be an iron-clad guarantee, due not only to the possibility of
random hardware failure, but also the possibility of human error in the design of: your
model, NetLogo, your Java VM, your hardware, and so on.
Will NetLogo and NetLogo 3D remain separate?
For now, yes. NetLogo 3D is included with NetLogo, but it is still a separate application.
Ideally a single unified application would support both 2D and 3D modeling. We would design
the 3D world support so it doesn't get in the way when you are building 2D models. Models
built in NetLogo 3D might require changes in order to run in the hypothetical unified
application.
Can I run NetLogo on my phone or tablet?
No. Neither iOS, nor Android, nor Windows RT supports running Java applications such as
NetLogo.
We are working on an alternate implementation of NetLogo on a JavaScript and HTML5
base, instead of Java. It will work on a variety of tablets and phones. We don't know yet when
it will be ready, and we expect that for a long time it will only support a subset of the features
in desktop NetLogo. The many person-years of development effort that have gone into the
Java version can't cheaply or easily be replicated on another platform.
For technical details on this new project, go here.
Downloading
Can I have multiple versions of NetLogo installed at the same time?
Yes. When you install NetLogo, the folder that is created contains has the version number in
its name, so multiple versions can coexist.
On Windows systems, whichever version you installed last will be the version that opens
when you double click a model file in Windows Explorer. On Macs, you can control what
version opens via "Get Info" in the Finder.
I'm on a UNIX system and I can't untar the download. Why?
Some of the files in the tarball have long pathnames, too long for the standard tar format. You
must use the GNU version of tar instead (or another program which understands the GNU tar
extensions). On some systems, the GNU version of tar is available under the name "gnutar".
You can find out if you are already using the GNU version by typing tar --version and
seeing if the output says "tar (GNU tar)".
How do I install NetLogo unattended
It depends on which platform you are using.
Linux: Untar NetLogo into the appropriate place.
Mac: Copy the NetLogo directory from the disk image into the Applications folder.
Windows:
Run the installer from the command line using the -q option:
NetLogo6.0.1Installer.exe -q
Running
Can I run NetLogo from a CD, a network drive, or a USB drive?
Yes. NetLogo runs fine from any file system, including read-only file systems.
Why is NetLogo so much slower when I unplug my Windows laptop?
Your computer is switching to power saving mode when unplugged. It's normal for this to
reduce speed a little, but unfortunately there is a bug in Java that drastically slows down
Swing applications, including NetLogo.
One workaround is to change the power settings on your computer so it doesn't go into power
saving mode when you unplug it. (If you do this, your battery won't last as long.)
Another workaround is to run NetLogo with an option recommended by Oracle, by editing the
NetLogo 6.0.1.vmoptions file, found in the NetLogo directory (under Program Files on your
hard drive, unless you installed NetLogo in a different location). Add on a new line:
-Dsun.java2d.ddoffscreen=false
You can see the details of the Java bug and vote for Oracle to fix it here.
Why does NetLogo bundle Java?
Since Mac OS X Lion, Apple have encouraged Mac application developers to bundle Java.
NetLogo bundles Java because it allows us to deliver a consistent, convenient experience to
our users. Bundling Java allows us to test for compatibility once and avoid any bugs caused
by version mismatches or Java configuration incompatibilities.
If users are interested in using Java on their system instead of the version of Java bundled
with NetLogo, they can configure NetLogo to use a different Java runtime. Please note that
this change is done at your own risk. We are unable to offer support for problems caused
by running NetLogo with an alternate Java Runtime. To change the Java runtime used by
NetLogo, open the NetLogo.cfg file and modify the app.runtime property to the path of your
preferred Java Runtime.
How come NetLogo won't start up on my Linux machine?
We bundle Oracle's Java runtime when using NetLogo on Linux. If you would like to change
the version of linux used, you can modify the .cfg files to point to a different version of java
(see How big can my model be? for more information).
In theory, any Java 8 or later runtime will run NetLogo. In practice, some Java
implementations aren't high enough quality. Recent versions of OpenJDK should work; older
ones may not. GNU libgcj does not work.
Ubuntu users should consult http://help.ubuntu.com/community/Java.
When I try to install NetLogo on Windows, I see "Windows protected
your PC"
Windows attempts to protect users from downloading malicious software by maintaining a list
of "good" and "malicious" software. The first users to install any NetLogo release will see this
warning. Later users may or may not see this warning. Before going any further, ensure you
are protected. The CCL can only vouch for NetLogo downloads hosted on the CCL Website.
NetLogo can be freely downloaded from the official NetLogo download page. If you obtain
NetLogo from anywhere else, you install it at your own risk!
You can continue past the Windows prompt by taking the following steps:
In the "Windows protected your PC" prompt, click "More Info", the prompt will change
In the changed prompt, click "Run Anyway" and continue with installation as normal
Note in order to see the "More Info" or "Run Anyway" options, you will need to run the
installer as an administrator. If you do not see those options, right-click and choose "Run as
administrator" and/or change your user account to an administrator account before installing.
We at the CCL are working on solving this problem and hope to free our users of the added
installation difficulty soon!
When I try to start NetLogo on Windows I get an error "The JVM
could not be started". Help!
A nearly certain fix is to use a text editor to edit the NetLogo.cfg file, changing 1024m to a
smaller number, like 512m. This should permit NetLogo to start, although the lower heap size
limit may affect your ability to run models with many agents. See How big can my model be?
for information on model size and how to edit the cfg file.
If running with the lower heap size limit is unacceptable, read on.
Some Windows systems have trouble allocating large amounts of contiguous virtual memory.
Upgrading to a newer version of Windows may help.
Running Windows in 64-bit mode instead of 32-bit mode may also help. Double check that
Windows is actually running in 64-bit mode; see Microsoft's FAQ page on 64-bit Windows.
NetLogo won't start on Mac OS Sierra (or later)
Some users have reported problems opening NetLogo 6 on Mac OS Sierra. We've been
unable to determine a root cause for this problem, but we're continuing to investigate. We're
looking for assistance from you if you run into this problem. It would be extremely helpful if
you could run the following command in the "Terminal" application and send the output in an
email to bugs@ccl.northwestern.edu.
xattr -pl com.apple.quarantine /Applications/NetLogo\ 6.0/NetLogo\ 6.0.app
running it should give you a single line of output (something like com.apple.quarantine:
01e1;58ac6af2;Firefox;F2E0B1E2-D203-4B05-8DF9-ABA58B52EFEA, but yours will have different
numbers, letters, and words). Please copy and paste this string into the email you send us.
There is also a partial workaround! Running the following command in the Terminal will
enable users to run NetLogo without turning Gatekeeper completely off. The command is:
sudo xattr -dr com.apple.quarantine /Applications/NetLogo\ 6.0/NetLogo\ 6.0.app
Note that if you plan to run NetLogo 3D, HubNet Client, or NetLogo Logging, you may also
need to re-run that command once for each of those applications. If the workaround was not
effective for you, please send us an email and let us know.
NetLogo won't start on Windows or crashes suddenly on Mac OS
Sierra
Some users on Mac OS with discrete graphics cards experience sudden crashes of NetLogo
when switching between integrated and discrete graphics. It's possible to prevent these
crashes by disabling automatic graphics switching in System Preferences.
Some Windows users may also be unable to open NetLogo due to graphics card settings or
drivers. If you are unable to open NetLogo on Windows, you might be able to fix this by
updating or reinstalling your graphics driver and/or disabling any graphics card utilities.
Because NetLogo might be unable to start for a number of reasons, we encourage you to
contact us if these steps aren't effective in resolving the problem.
Can I run NetLogo from the command line, without the GUI?
Yes. The easiest way is to set up your model run or runs as a BehaviorSpace experiment. No
additional programming is required. See the BehaviorSpace Guide for details.
Another option is to use our Controlling API. Some light Java programming is required. See
the Controlling API Guide for details and sample code.
Does NetLogo take advantage of multiple processors?
Only when using BehaviorSpace. BehaviorSpace does parallel runs, one per processor.
For a single model run, only one processor is used.
We are seeking funding to make it possible to split a single model run across multiple
processors or multiple computers.
Can I distribute NetLogo model runs across a cluster or grid of
computers?
Many of the same comments in the previous answer apply. It is not possible to split a single
model run across multiple computers, but you can have each machine in a cluster doing one
or more separate, independent model runs, using either BehaviorSpace or our Controlling
API. We don't have automated support for splitting the runs across clusters, so you'll need to
arrange that yourself.
Various users are already using NetLogo on clusters, with a variety of hardware and software.
You can seek them out on the NetLogo Users Group.
Is there any way to recover lost work if NetLogo crashes or freezes?
Yes. NetLogo auto-saves files as you are working on them. The path to the auto-save file
depends on whether or not the NetLogo model has been saved.
For NetLogo models which have been saved, a hidden file with the name
".filename.tmp.nlogo" will be created in the same directory as the NetLogo model.
For unsaved NetLogo models, autosave files can be found in your OS-specific java temporary
directory. The files are named according to the following format: autosave_yyyy-MMdd.HH_mm_ss.nlogo where the time and date are the time and date the model was opened.
The exact path will depend on your operating system:
On Mac OS, the temporary directory is /var/folders/68/<30-character-alphanumericsequence>/T/ . The 30-character-alphanumeric-sequence is unique to each machine.
On Windows the logs can be found in C:\Users\\AppData\Local\Temp, where
is the logged in user.
On most non-Mac Unix-like systems the temp directory is /tmp.
Usage
When I move the speed slider all the way to the right, why does my
model seem to stop?
The only way NetLogo can make your model run faster is by updating the view less
frequently. As you move the speed slider to the right, view updates become less and less
frequent. Since view updates take time, that means more speed.
However, fewer updates also means that the updates come farther apart. When several
seconds pass between updates, it may seem like your model has stopped. It hasn't. It's
running at full speed. Watch the tick counter! (If your model uses it. If it doesn't, watch
something else, like a plot.)
To get a feel for what's going on, try moving the slider to the right gradually rather than
suddenly. If you find the updates too infrequent at the rightmost position, just don't push the
slider that far.
Can I use the mouse to "paint" in the view?
NetLogo does not have a built-in set of painting tools for painting in the view. But with only a
few lines of code, you can add painting capability to your model. To see how it's done, look at
Mouse Example, in the Code Examples section of the Models Library. The same techniques
can be used to let the user interact with your model using the mouse in other ways, too.
Another possibility is to create an image in another program and import it using the import
items on the File menu or the import-* primitives.
How big can my model be? How many turtles, patches, procedures,
buttons, and so on can my model contain?
We have tested NetLogo with models that use hundreds of megabytes of RAM and they work
fine. We haven't tested models that use gigabytes of RAM, though. Theoretically it should
work, but you might hit some limits that are inherent in the underlying Java VM and/or
operating system (either designed-in limits, or bugs).
The NetLogo engine has no fixed limits on size. By default, though, NetLogo ships with a onegigabyte ceiling on how much total RAM it can use. If your model exceeds that limit, you'll get
an OutOfMemoryError dialog.
If you are using BehaviorSpace, note that doing runs in parallel will multiply your RAM usage
accordingly.
Each platform contains ".cfg" files containing JVM settings. There is one cfg file for each subapplication (NetLogo, NetLogo 3D, HubNet Client, etc.) Although the file location varies by
platform, the process for changing it is the same. Locate the section of the file that looks like
the following:
[JVMOptions]
# there may be one or more lines, leave them unchanged
-Xmx1024m
# there may be one or more lines, leave them unchanged
Modify the value immediately following
-Xmx
, changing it to the amount of space you need, save the file, and restart NetLogo. Platform
specific notes follow:
Windows: The cfg files will be in
C:\Program Files (x86)\NetLogo 6.0.1\app
if you are running 64-bit windows, and
C:\Program Files\NetLogo 6.0.1\app
otherwise.
Mac OS X: The file for NetLogo will be located at:
/Application/NetLogo 6.0.1/NetLogo.app/Contents/Java/NetLogo.cfg
For NetLogo 3D and the other applications, you will find the file in the corresponding
location for each application package. You can reach the cfg file by control-clicking the
application in the Finder and choosing "Show Package Contents" from the popup menu.
Please note that depending on your version of Mac OS X, changing the cfg file *may*
break application signing. If this happens, follow Apple's directions on this page to
temporarily allow apps from "Anywhere", run NetLogo once, then restore the setting to
"Mac App Store and Identified Developers".
Other: The cfg files will be located in the
netlogo-6.0.1/app
folder after untarring.
By default, Mac builds of NetLogo bundle a 64-bit JVM, which should be able to make use of
as much memory as the lesser of available system memory and the value following
-Xmx
. Windows and Linux will bundle a 32-bit or 64-bit JVM, depending on which version you have
downloaded. It is recommended that you install 64-bit NetLogo on all 64-bit operating systems
for best performance.
Can I use GIS data in NetLogo?
Yes, many users are using GIS data with NetLogo. The most complete way to do that is with
the GIS extension. See the GIS Extension Guide.
A simpler way is to use import-pcolors , but that only works for importing maps that are
images, not maps in other formats.
It is also possible to write NetLogo code that reads GIS data using our file I/O primitives such
as file-open. For example, see the Grand Canyon model in the Earth Science section of
Sample Models.
My model runs slowly. How can I speed it up?
Here's some ways to make it run faster without changing the structure of the code:
Use tick-based view updates, not continuous updates.
Decrease the frequency of view updates by pushing the speed slider to the right, or turn
updates off using the checkbox.
If your model is using all available RAM on your computer, then installing more RAM
should help. If your hard drive makes a lot of noise while your model is running, you
probably need more RAM.
Use turtle size 1, 1.5, or 2, as the 2D renderings for these sizes are cached by NetLogo.
(This only affects graphics speed in the 2D view, not computation speed.)
In many cases, though, if you want your model to run faster, you may need to make some
changes to the code. Usually the most obvious opportunity for speedup is that you're doing
too many computations that involve all the turtles or all the patches. Often this can be reduced
by reworking the model so that it does less computation per time step. The members of the
NetLogo Users Group may be able to help with this.
The profiler extension is useful for identifying which parts of your code are taking the most
time.
Unless you are running the exact same strings over and over, using run and runresult are
much slower than running code directly; you should avoid using these primitives on fresh
strings in performance-critical code.
Can I have more than one model open at a time?
One instance of NetLogo can only have one model open at a time. (Unfortunately, it is unlikely
that this will change in a future version, due to the engineering difficulties involved.)
You can have multiple models open by opening multiple instances of NetLogo, though. On
Windows and Linux, simply start the application again. On a Mac, you'll need to duplicate the
application (not the whole folder, just the application itself) in the Finder, then open the copy.
(The copy takes up only a very small amount of additional disk space.)
Can I change the choices in a chooser on the fly?
No.
Can I divide the code for my model up into several files?
On an experimental basis, this is available using the __includes keyword.
Programming
How does the NetLogo language differ from other Logos?
This is answered in detail at the end of the Programming Guide.
How come my model from an earlier NetLogo doesn't work right?
See the Transition Guide for help.
How do I take the negative of a number?
Any of these ways:
(- x)
-1 * x
0 - x
With the first way, the parentheses are required.
My turtle moved forward 1, but it's still on the same patch. Why?
If you have disabled wrapping at the world edges in your model, then the turtle might be at a
world edge and unable to move any further. You can test for this using can-move?.
Assuming the turtle isn't hitting a world edge, moving forward 1 is only guaranteed to take a
turtle to a new patch if the turtle's heading is a multiple of 90 (that is, exactly north, south,
east, or west).
It's because the turtle might not be standing in the center of a patch. It might be near the
corner of a patch. For example, suppose your turtle is close to the southwest corner of a
patch and is facing northeast. The length of the patch diagonal is 1.414... (the square root of
two), so fd 1 will leave the turtle near the northeast corner of the same patch.
If you don't want to have to think about these issues, one possibility is to write your model in
such a way that your turtles always come to rest on patch centers. See next question.
How do I keep my turtles on patch centers?
A turtle is on a patch center when its xcor and ycor are integers.
You can move a turtle to the center of its current patch with either of these two equivalent
commands:
move-to patch-here
setxy pxcor pycor
But you'll never need to do that if you never allow turtles off of patch centers in the first place.
The sprout command creates turtles on patch centers. For example:
ask n-of 50 patches [ sprout 1 [ face one-of neighbors4 ] ]
Another way for a turtle to start on a patch center is with a command such as this line of turtle
code, which moves it to the center of a random patch:
move-to one-of patches
Once a turtle is on a patch center, as long as its heading always stays an exact multiple of 90
(that is to say, due north, east, south, or west), and as it long as it moves forward or back by
integer amounts, it will always land on patch centers.
See Random Grid Walk Example, in the Code Examples section of the Models Library, to see
these code snippets in use.
is reporting the same patch my turtle is already
standing on. Why?
patch-ahead 1
See the answer two answers up. It's the same issue.
This might not be the meaning of "ahead" you were expecting. With patch-ahead, you must
specify the distance ahead that you want to look. If you want to know the next patch a turtle
would cross into if it moved forward continuously, it is possible to find that out. See Next Patch
Example, in the Code Examples section of the Models Library.
How do I give my turtles "vision"?
You can use in-radius to let a turtle see a circular area around it.
Several primitives let the turtle "look" at specific points. The patch-ahead primitive is useful for
letting a turtle see what is directly in front of it. If you want the turtle to look in another direction
besides straight ahead, try patch-left-and-ahead and patch-right-and-ahead.
If you want the turtle to have a full "cone" of vision, use the in-cone primitive.
You can also find out the next patch a turtle would cross into if it moved forward continuously.
See Next Patch Example, in the Code Examples section of the Models Library.
Can agents sense what's in the drawing layer?
No. If you want to make marks that agents can sense, use patch colors.
I'm getting numbers like 0.10000000004 and 0.799999999999 instead
of 0.1 and 0.8. Why?
See the "Math" section of the Programming Guide for a discussion of this issue.
The documentation says that random-float 1 might return 0 but will
never return 1. What if I want 1 to be included?
It really doesn't matter. Even if 1 were a possible result, it would only come up approximately
1 in 2^64 tries, which means you'd be waiting hundreds of years before it ever came up
exactly 1.
Nonetheless, if you are convinced that it really must be possible to get 1, you can use
precision to round your answer to a certain number of decimal places. For example:
print precision (random-float 1) 10
0.2745173723
(If you use this method, note that 0 and 1 are only half as likely to come up as other answers.
To see why this is so, consider the case where you only keep one digit after the decimal
point. Results between 0 and 0.5 get rounded to 0, but results between 0.5 and 1.5 get
rounded to 1; the latter range is twice as large. If you want 0, 0.1, 0.2, ..., 0.9, and 1 to all be
equally likely, an alternative is to write random 11 / 10 ; this gives all 11 answers with equal
probability.)
How can I keep two turtles from occupying the same patch?
See One Turtle Per Patch Example, in the Code Examples section of the Models Library.
How can I find out if a turtle is dead?
When a turtle dies, it turns into nobody. nobody is a special value used in NetLogo used to
indicate the absence of a turtle or patch. So for example:
if turtle 0 != nobody [ ... ]
You could also use is-turtle?:
if is-turtle? turtle 0 [ ... ]
Does NetLogo have arrays?
Nearly all models should just use lists for this.
The usual motivation for using arrays in other programming languages is that they provide
fast random access (item) and mutation (replace-item). But NetLogo's lists, even though they
are immutable, now provide near constant time performance on these operations.
Lists in earlier versions of NetLogo (4.1 and 4.0) were simple singly-linked lists and therefore
these operations took linear time. The data structure underlying NetLogo's lists now is the
immutable Vector class from the Scala collections library. It uses 32-wide hash array mapped
tries, as implemented by Tiark Rompf, based in part on work by Phil Bagwell and Rich Hickey.
If you are certain you want to use raw, mutable JVM arrays in your model, they are provided
by the array extension. See the Arrays & Tables section of the User Manual.
Does NetLogo have hash tables or associative arrays?
Yes, using the table extension. See the Arrays & Tables section of the User Manual.
How can I use different patch "neighborhoods" (circular, Von
Neumann, Moore, etc.)?
The in-radius primitives lets you access circular neighborhoods of any radius.
The neighbors primitive gives you a Moore neighborhood of radius 1, and the neighbors4
primitive gives you a Von Neumann neighborhood of radius 1.
For Moore or Von Neumann neighborhoods of a larger radius, see Moore & Von Neumann
Example in the Code Examples section of the Models Library.
How can I convert an agentset to a list of agents, or vice versa?
If you want the list in a particular order, use the sort or sort-by primitives. The Lists section of
the Programming Guide explains how to do this. See also Ask Ordering Example, in the Code
Examples section of the Models Library.
If you want the list in a random order, here's how:
[self] of
Because all operations on agentsets are in random order, the resulting list is in random order.
To convert a list of agents to an agentset, use the turtle-set, patch-set, or link-set
primitives.
How do I stop foreach?
To stop a foreach from executing you need to define a separate procedure that contains only
the foreach, for example:
to test
foreach [1 2 3] [
if ? = 2 [ stop ]
print ?
]
end
This code will only print the number 1. The stop returns from the current procedure so nothing
after the foreach will be executed either. (If the procedure is a reporter procedure, use report
instead of stop.)
I'm trying to make a list. Why do I keep getting the error "Expected a
constant"?
If a list contains only constants, you can write it down just by putting square brackets around
it, like [1 2 3] .
If you want your list to contain items that may vary at runtime, the list cannot be written down
directly. Instead, you build it using the list primitive.
BehaviorSpace
Why are the rows in my BehaviorSpace table results out of order?
This is normal when doing multiple runs in parallel. For a discussion of the issue, see the
section on parallel runs in the BehaviorSpace Guide section of the User Manual.
How do I measure runs every n ticks?
Use repeat in your experiment's go commands, e.g.:
repeat 10 [ go ]
to measure the run after every 10 ticks. Essentially you are making one experiment step
equal 10 ticks.
I'm varying a global variable I declared in the Code tab, but it doesn't
work. Why?
It's probably because your setup commands or setup procedure are using clear-all, causing
the values set by BehaviorSpace to be cleared.
One possible workaround is to change your experiment's setup commands to preserve the
value of the variable, e.g.:
let old-var1 var1
setup
set var1 old-var1
This works because even clear-all doesn't clear the values of local variables made with let
Another possible workaround is to change your model's setup procedure to use more specific
clearing commands to clear only what you want cleared.
Why are some of my results cut off in Excel?
In some versions of Excel, spreadsheets can't have more than 256 columns. (See a Microsoft
support article on the subject.)
Possible workarounds include:
Use a newer version of Excel, such as Excel 2007 (Windows) or Excel 2008 (Mac).
Use a different program besides Excel.
Ask BehaviorSpace to generate results in table format instead of, or in addition to,
spreadsheet format. (Excel can read our table format, too.)
Change your experiment so the result has fewer columns.
NetLogo 3D
Does NetLogo work with my stereoscopic device?
NetLogo supports fullscreen exclusive mode. If that is all your device needs then, possibly
yes. However, it can be tricky to get it working. We don't have any such devices so it is difficult
for us to make the process easier. If your device needs something else, for example,
quadbuffers enabled, the answer is probably no.
Extensions
I'm writing an extension. Why does the compiler say it can't find
org.nlogo.api?
You need to add NetLogo.jar to your classpath when compiling. NetLogo.jar is included with
NetLogo.
NetLogo Dictionary
Alphabetical: A B C D E F G H I J L M N O P R S T U V W X Y ->
Categories: Turtle - Patch - Links - Agentset - Color - Anonymous Procedures - Control/Logic - World
Perspective - Input/Output - File - List - String - Math - Plotting - System - HubNet
Special: Variables - Keywords - Constants
Categories
This is an approximate grouping. Remember that a turtle-related primitive might still be used by patches or the observer, and vice versa. To
see which agents (turtles, patches, links, observer) can actually run a primitive, consult its dictionary entry.
Turtle-related
back (bk) -at -here -on can-move? clear-turtles (ct) create- create-ordered- create-orderedturtles (cro) create-turtles (crt) die distance distancexy downhill downhill4 dx dy face facexy forward (fd) hatch hatch- hide-turtle (ht)
home inspect is-? is-turtle? jump layout-circle left (lt) move-to myself nobody no-turtles of other patch-ahead patch-at patch-atheading-and-distance patch-here patch-left-and-ahead patch-right-and-ahead pen-down (pd) pen-erase (pe) pen-up (pu) random-xcor
random-ycor right (rt) self set-default-shape __set-line-thickness setxy shapes show-turtle (st) sprout sprout- stamp stamp-erase
stop-inspecting subject subtract-headings tie towards towardsxy turtle turtle-set turtles turtles-at turtles-here turtles-on turtles-own untie uphill
uphill4
Patch-related
clear-patches (cp) diffuse diffuse4 distance distancexy import-pcolors import-pcolors-rgb inspect is-patch? myself neighbors neighbors4
nobody no-patches of other patch patch-at patch-ahead patch-at-heading-and-distance patch-here patch-left-and-ahead patch-right-andahead patch-set patches patches-own random-pxcor random-pycor self sprout sprout- stop-inspecting subject turtles-here
Link-related
both-ends clear-links create--from create--from create--to create--to create--with create-with create-link-from create-links-from create-link-to create-links-to create-link-with create-links-with die hide-link in-neighbor? in--neighbors in--from in-link-neighbor? in-link-neighbors in-link-from is-directed-link? is-link? is-link-set? is-? is-undirected-link? layout-radial layout-spring layout-tutte -neighbor? -neighbors -with link-heading linklength link-neighbor? link links links-own -own link-neighbors link-with my- my-in- my-in-links my-links myout- my-out-links no-links other-end out--neighbor? out--neighbors out--to out-link-neighbor? out-linkneighbors out-link-to show-link tie untie
Agentset
all? any? ask ask-concurrent at-points -at -here -on count in-cone in-radius is-agent? is-agentset? is-patch-set?
is-turtle-set? link-set max-n-of max-one-of member? min-n-of min-one-of n-of neighbors neighbors4 no-links no-patches no-turtles of one-of
other patch-set patches sort sort-by sort-on turtle-set turtles turtles-at turtles-here turtles-on with with-max with-min
Color
approximate-hsb approximate-rgb base-colors color extract-hsb extract-rgb hsb import-pcolors import-pcolors-rgb pcolor rgb scale-color
shade-of? wrap-color
Control flow and logic
and ask ask-concurrent carefully end error error-message every if ifelse ifelse-value let loop not or repeat report run runresult ; (semicolon) set
stop startup to to-report wait while with-local-randomness without-interruption xor
Anonymous Procedures
-> (anonymous procedure) filter foreach is-anonymous-command? is-anonymous-reporter? map n-values reduce run runresult sort-by
World
clear-all (ca) clear-drawing (cd) clear-globals clear-patches (cp) clear-ticks clear-turtles (ct) display import-drawing import-pcolors importpcolors-rgb no-display max-pxcor max-pycor min-pxcor min-pycor patch-size reset-ticks resize-world set-patch-size stop-inspecting-deadagents tick tick-advance ticks world-width world-height
Perspective
follow follow-me reset-perspective (rp) ride ride-me subject watch watch-me
HubNet
hubnet-broadcast hubnet-broadcast-clear-output hubnet-broadcast-message hubnet-clear-override hubnet-clear-overrides hubnet-clients-list
hubnet-enter-message? hubnet-exit-message? hubnet-kick-all-clients hubnet-kick-client hubnet-fetch-message hubnet-message hubnetmessage-source hubnet-message-tag hubnet-message-waiting? hubnet-reset hubnet-reset-perspective hubnet-send hubnet-send-clearoutput hubnet-send-follow hubnet-send-message hubnet-send-override hubnet-send-watch
Input/output
beep clear-output date-and-time export-view export-interface export-output export-plot export-all-plots export-world import-drawing import-
pcolors import-pcolors-rgb import-world mouse-down? mouse-inside? mouse-xcor mouse-ycor output-print output-show output-type outputwrite print read-from-string reset-timer set-current-directory show timer type user-directory user-file user-new-file user-input user-message
user-one-of user-yes-or-no? write
File
file-at-end? file-close file-close-all file-delete file-exists? file-flush file-open file-print file-read file-read-characters file-read-line file-show filetype file-write user-directory user-file user-new-file
List
but-first but-last empty? filter first foreach fput histogram is-list? item last length list lput map max member? min modes n-of n-values of
position one-of range reduce remove remove-duplicates remove-item replace-item reverse sentence shuffle sort sort-by sort-on sublist
String
Operators (<, >, =, !=, <=, >=) but-first but-last empty? first is-string? item last length member? position remove remove-item read-from-string
replace-item reverse substring word
Mathematical
Arithmetic Operators (+, *, -, /, ^, <, >, =, !=, <=, >=)abs acos asin atan ceiling cos e exp floor int is-number? ln log max mean median min mod
modes new-seed pi precision random random-exponential random-float random-gamma random-normal random-poisson random-seed
remainder round sin sqrt standard-deviation subtract-headings sum tan variance
Plotting
autoplot? auto-plot-off auto-plot-on clear-all-plots clear-plot create-temporary-plot-pen export-plot export-all-plots histogram plot plot-name
plot-pen-exists? plot-pen-down plot-pen-reset plot-pen-up plot-x-max plot-x-min plot-y-max plot-y-min plotxy set-current-plot set-current-plotpen set-histogram-num-bars set-plot-pen-color set-plot-pen-interval set-plot-pen-mode set-plot-x-range set-plot-y-range setup-plots updateplots
BehaviorSpace
behaviorspace-experiment-name behaviorspace-run-number
System
netlogo-version netlogo-web?
Built-In Variables
Turtles
breed color heading hidden? label label-color pen-mode pen-size shape size who xcor ycor
Patches
pcolor plabel plabel-color pxcor pycor
Links
breed color end1 end2 hidden? label label-color shape thickness tie-mode
Other
->
Keywords
breed directed-link-breed end extensions globals __includes links-own patches-own to to-report turtles-own undirected-link-breed
Constants
Mathematical Constants
e = 2.718281828459045
pi = 3.141592653589793
Boolean Constants
false
true
Color Constants
black = 0
gray = 5
white = 9.9
red = 15
orange = 25
brown = 35
yellow = 45
green = 55
lime = 65
turquoise = 75
cyan = 85
sky = 95
blue = 105
violet = 115
magenta = 125
pink = 135
See the Colors section of the Programming Guide for more details.
A
abs
Since 1.0
abs number
Reports the absolute value of number.
show abs -7
=> 7
show abs 5
=> 5
acos
Since 1.3
acos number
Reports the arc cosine (inverse cosine) of the given number. The input must be in the range -1 to 1. The result is in degrees, and lies in the
range 0 to 180.
all?
Since 4.0
all? agentset [reporter]
Reports true if all of the agents in the agentset report true for the given reporter. Otherwise reports false as soon as a counterexample is
found.
If the agentset is empty, reports true.
The reporter must report a boolean value for every agent (either true or false), otherwise an error occurs.
if all? turtles [color = red]
[ show "every turtle is red!" ]
See also any?.
and
Since 1.0
condition1 and condition2
Reports true if both condition1 and condition2 are true.
Note that if condition1 is false, then condition2 will not be run (since it can't affect the result).
if (pxcor > 0) and (pycor > 0)
[ set pcolor blue ] ;; the upper-right quadrant of
;; patches turn blue
any?
Since 2.0
any? agentset
Reports true if the given agentset is non-empty, false otherwise.
Equivalent to "count agentset > 0", but more efficient (and arguably more readable).
if any? turtles with [color = red]
[ show "at least one turtle is red!" ]
Note: nobody is not an agentset. You only get nobody back in situations where you were expecting a single agent, not a whole agentset. If
any? gets nobody as input, an error results.
See also all?, nobody.
approximate-hsb
Since 4.0
approximate-hsb hue saturation brightness
Reports a number in the range 0 to 140, not including 140 itself, that represents the given color, specified in the HSB spectrum, in NetLogo's
color space.
The first value (hue) should be in the range of 0 to 360, the second and third (saturation and brightness) in the range between 0 and 100.
The color reported may be only an approximation, since the NetLogo color space does not include all possible colors.
show approximate-hsb 0 0 0
=> 0 ;; (black)
show approximate-hsb 180 57.143 76.863
=> 85 ;; (cyan)
See also extract-hsb, approximate-rgb, extract-rgb.
approximate-rgb
Since 4.0
approximate-rgb red green blue
Reports a number in the range 0 to 140, not including 140 itself, that represents the given color, specified in the RGB spectrum, in NetLogo's
color space.
All three inputs should be in the range 0 to 255.
The color reported may be only an approximation, since the NetLogo color space does not include all possible colors. (See approximate-hsb
for a description of what parts of the HSB color space NetLogo colors cover; this is difficult to characterize in RGB terms.)
show approximate-rgb 0 0 0
=> 0 ;; black
show approximate-rgb 0 255 255
=> 85.2 ;; cyan
See also extract-rgb, approximate-hsb, and extract-hsb.
Arithmetic Operators
+
*
/
^
<
>
=
!=
<=
>=
Since 1.0
Since 1.0
Since 1.0
Since 1.0
Since 1.0
Since 1.0
Since 1.0
Since 1.0
Since 1.0
Since 1.0
Since 1.0
All of these operators take two inputs, and all act as "infix operators" (going between the two inputs, as in standard mathematical use).
NetLogo correctly supports order of operations for infix operators.
The operators work as follows: + is addition, * is multiplication, - is subtraction, / is division, ^ is exponentiation, < is less than, > is greater
than, = is equal to, != is not equal to, <= is less than or equal, >= is greater than or equal.
Note that the subtraction operator (-) always takes two inputs unless you put parentheses around it, in which case it can take one input. For
example, to take the negative of x, write (- x), with the parentheses.
All of the comparison operators also work on strings.
All of the comparison operators work on agents. Turtles are compared by who number. Patches are compared top to bottom left to right, so
patch 0 10 is less than patch 0 9 and patch 9 0 is less than patch 10 0. Links are ordered by end points and in case of a tie by breed. So link
0 9 is before link 1 10 as the end1 is smaller, and link 0 8 is less than link 0 9. If there are multiple breeds of links unbreeded links will come
before breeded links of the same end points and breeded links will be sorted in the order they are declared in the Code tab.
Agentsets can be tested for equality or inequality. Two agentsets are equal if they are the same type (turtle or patch) and contain the same
agents.
If you are not sure how NetLogo will interpret your code, you should add parentheses.
show 5 * 6 + 6 / 3
=> 32
show 5 * (6 + 6) / 3
=> 20
Many extension objects may be tested for equality and inequality using = and !=. For instance, the array, matrix, and table objects returned by
their respective extensions may be compared for equality / inequality. Extension objects may not be tested using <, >, <=, or >=.
asin
Since 1.3
asin number
Reports the arc sine (inverse sine) of the given number. The input must be in the range -1 to 1. The result is in degrees, and lies in the range
-90 to 90.
ask
Since 1.0
ask agentset [commands]
ask agent [commands]
The specified agent or agentset runs the given commands.
ask turtles [ fd 1 ]
;; all turtles move forward one step
ask patches [ set pcolor red ]
;; all patches turn red
ask turtle 4 [ rt 90 ]
;; only the turtle with id 4 turns right
Note: only the observer can ask all turtles or all patches. This prevents you from inadvertently having all turtles ask all turtles or all patches
ask all patches, which is a common mistake to make if you're not careful about which agents will run the code you are writing.
Note: Only the agents that are in the agentset at the time the ask begins run the commands.
ask-concurrent
Since 4.0
ask-concurrent agentset [commands]
This primitive exists only for backwards compatibility. We don't recommend using it new models.
The agents in the given agentset run the given commands, using a turn-taking mechanism to produce simulated concurrency. See the AskConcurrent section of the Programming Guide for details on how this works.
Note: Only the agents that are in the agentset at the time the ask begins run the commands.
See also without-interruption.
at-points
Since 1.0
agentset at-points [[x1 y1] [x2 y2] ...]
Reports a subset of the given agentset that includes only the agents on the patches at the given coordinates (relative to this agent). The
coordinates are specified as a list of two-item lists, where the two items are the x and y offsets.
If the caller is the observer, then the points are measured relative to the origin, in other words, the points are taken as absolute patch
coordinates.
If the caller is a turtle, the points are measured relative to the turtle's exact location, and not from the center of the patch under the turtle.
ask turtles at-points [[2 4] [1 2] [10 15]]
[ fd 1 ] ;; only the turtles on the patches at the
;; coordinates (2,4), (1,2) and (10,15),
;; relative to the caller, move
atan
Since 1.0
atan x y
Converts x and y offsets to a turtle heading in degrees (from 0 to 360).
Note that this version of atan is designed to conform to the geometry of the NetLogo world, where a heading of 0 is straight up, 90 is to the
right, and so on clockwise around the circle. (Normally in geometry an angle of 0 is right, 90 is up, and so on, counterclockwise around the
circle, and atan would be defined accordingly.)
When y is 0: if x is positive, it reports 90; if x is negative, it reports 270; if x is zero, you get an error.
show atan 1 -1
=> 135
show atan -1 1
=> 315
crt 1 [ set heading 30
=> 30
fd 1
print atan xcor ycor ]
In the final example, note that the result of atan equals the turtle's heading.
If you ever need to convert a turtle heading (obtained with atan or otherwise) to a normal mathematical angle, the following should be helpful:
to-report heading-to-angle [ h ]
report (90 - h) mod 360
end
autoplot?
Since 1.0
autoplot?
Reports true if auto-plotting is on for the current plot, false otherwise.
auto-plot-off
auto-plot-on
Since 1.0
Since 1.0
auto-plot-off
auto-plot-on
This pair of commands is used to control the NetLogo feature of auto-plotting in the current plot. Auto-plotting will automatically update the x
and y axes of the plot whenever the current pen exceeds these boundaries. It is useful when wanting to show all plotted values in the current
plot, regardless of the current plot ranges.
B
back
bk
Since 1.0
Since 1.0
back number
The turtle moves backward by number steps. (If number is negative, the turtle moves forward.)
Turtles using this primitive can move a maximum of one unit per time increment. So bk 0.5 and bk 1 both take one unit of time, but bk 3
takes three.
If the turtle cannot move backward number steps because it is not permitted by the current topology the turtle will complete as many steps of
1 as it can and stop.
See also forward, jump, can-move?.
base-colors
Since 4.0
base-colors
Reports a list of the 14 basic NetLogo hues.
print base-colors
=> [5 15 25 35 45 55 65 75 85 95 105 115 125 135]
ask turtles [ set color one-of base-colors ]
;; each turtle turns a random base color
ask turtles [ set color one-of remove gray base-colors ]
;; each turtle turns a random base color except for gray
beep
Since 2.1
beep
Emits a beep. Note that the beep sounds immediately, so several beep commands in close succession may produce only one audible sound.
Example:
beep
repeat 3 [ beep ]
;;
;;
;;
repeat 3 [ beep wait 0.1 ] ;;
;;
emits one beep
emits 3 beeps at once,
so you only hear one sound
produces 3 beeps in succession,
separated by 1/10th of a second
When running headless, this command has no effect.
behaviorspace-experiment-name
Since 5.2
behaviorspace-experiment-name
Reports the current experiment name in the current experiment.
If no BehaviorSpace experiment is running, reports "".
behaviorspace-run-number
behaviorspace-run-number
Reports the current run number in the current BehaviorSpace experiment, starting at 1.
If no BehaviorSpace experiment is running, reports 0.
Since 4.1.1
both-ends
Since 4.0
both-ends
Reports the agentset of the 2 nodes connected by this link.
crt 2
ask turtle 0 [ create-link-with turtle 1 ]
ask link 0 1 [
ask both-ends [ set color red ] ;; turtles 0 and 1 both turn red
]
breed
breed
This is a built-in turtle and link variable. It holds the agentset of all turtles or links of the same breed as this turtle or link. (For turtles or links
that do not have any particular breed, this is the turtles agentset of all turtles or the links agentset of all links respectively.)
You can set this variable to change a turtle or link's breed. (When a turtle changes breeds, its shape is reset to the default shape for that
breed. See set-default-shape.)
See also breed, directed-link-breed, undirected-link-breed
Example:
breed [cats cat]
breed [dogs dog]
;; turtle code:
if breed = cats [ show "meow!" ]
set breed dogs
show "woof!"
directed-link-breed [ roads road ]
;; link code
if breed = roads [ set color gray ]
breed
breed []
This keyword, like the globals, turtles-own, and patches-own keywords, can only be used at the beginning of the Code tab, before any
procedure definitions. It defines a breed. The first input defines the name of the agentset associated with the breed. The second input defines
the name of a single member of the breed.
Any turtle of the given breed:
is part of the agentset named by the breed name
has its breed built-in variable set to that agentset
Most often, the agentset is used in conjunction with ask to give commands to only the turtles of a particular breed.
breed [mice mouse]
breed [frogs frog]
to setup
clear-all
create-mice 50
ask mice [ set color white ]
create-frogs 50
ask frogs [ set color green ]
show [breed] of one-of mice
show [breed] of one-of frogs
end
;; prints mice
;; prints frogs
show mouse 1
;; prints (mouse 1)
show frog 51
;; prints (frog 51)
show turtle 51
;; prints (frog 51)
See also globals, patches-own, turtles-own, -own, create-, -at, -here.
but-first
butfirst
bf
but-last
butlast
bl
but-first list
but-first string
but-last list
but-last string
Since 1.0
Since 1.0
Since 1.0
Since 1.0
Since 1.0
Since 1.0
When used on a list, but-first reports all of the list items of list except the first, and but-last reports all of the list items of list except the last.
On strings, but-first and but-last report a shorter string omitting the first or last character of the original string.
;; mylist is [2 4 6 5 8 12]
set mylist but-first mylist
;; mylist is now [4 6 5 8 12]
set mylist but-last mylist
;; mylist is now [4 6 5 8]
show but-first "string"
;; prints "tring"
show but-last "string"
;; prints "strin"
C
can-move?
Since 3.1
can-move? distance
Reports true if this turtle can move distance in the direction it is facing without violating the topology; reports false otherwise.
It is equivalent to:
patch-ahead distance != nobody
carefully
Since 2.1
carefully [ commands1 ] [ commands2 ]
Runs commands1. If a runtime error occurs inside commands1, NetLogo won't stop and alert the user that an error occurred. It will suppress
the error and run commands2 instead.
The error-message reporter can be used in commands2 to find out what error was suppressed in commands1. See error-message.
carefully [ print one-of [1 2 3] ] [ print error-message ]
=> 3
observer> carefully [ print one-of [] ] [ print error-message ]
=> ONE-OF got an empty list as input.
ceiling
Since 1.0
ceiling number
Reports the smallest integer greater than or equal to number.
show ceiling 4.5
=> 5
show ceiling -4.5
=> -4
See also floor, round, precision.
clear-all
ca
Since 1.0
Since 1.0
clear-all
Combines the effects of clear-globals, clear-ticks, clear-turtles, clear-patches, clear-drawing, clear-all-plots, and clear-output.
clear-all-plots
Since 1.0
clear-all-plots
Clears every plot in the model. See clear-plot for more information.
clear-drawing
cd
Since 3.0
Since 3.0
clear-drawing
Clears all lines and stamps drawn by turtles.
clear-globals
Since 5.2
clear-globals
Sets all global variables to 0.
clear-links
Since 4.0
clear-links
Kills all links.
See also die.
clear-output
Since 1.0
clear-output
Clears all text from the model's output area, if it has one. Otherwise does nothing.
clear-patches
cp
Since 1.0
Since 1.0
clear-patches
Clears the patches by resetting all patch variables to their default initial values, including setting their color to black.
clear-plot
clear-plot
In the current plot only, resets all plot pens, deletes all temporary plot pens, resets the plot to its default values (for x range, y range, etc.), and
resets all permanent plot pens to their default values. The default values for the plot and for the permanent plot pens are set in the plot Edit
dialog, which is displayed when you edit the plot. If there are no plot pens after deleting all temporary pens, that is to say if there are no
permanent plot pens, a default plot pen will be created with the following initial settings:
Pen: down
Color: black
Mode: 0 (line mode)
Name: "default"
Interval: 1
See also clear-all-plots.
clear-ticks
Since 5.0
clear-ticks
Clears the tick counter.
Does not set the counter to zero. After this command runs, the tick counter has no value. Attempting to access or update it is an error until
reset-ticks is called.
See also reset-ticks.
clear-turtles
ct
Since 1.0
Since 1.0
clear-turtles
Kills all turtles.
Also resets the who numbering, so the next turtle created will be turtle 0.
See also die.
color
color
This is a built-in turtle or link variable. It holds the color of the turtle or link. You can set this variable to make the turtle or link change color.
Color can be represented either as a NetLogo color (a single number), or an RGB color (a list of 3 numbers). See details in the Colors section
of the Programming Guide.
See also pcolor.
cos
Since 1.0
cos number
Reports the cosine of the given angle. Assumes the angle is given in degrees.
show cos 180
=> -1
count
Since 1.0
count agentset
Reports the number of agents in the given agentset.
show count turtles
;; prints the total number of turtles
show count patches with [pcolor = red]
;; prints the total number of red patches
create-ordered-turtles
cro
Since 4.0
Since 4.0
create-ordered-turtles number
create-ordered-turtles number [ commands ]
create-ordered number
create-ordered number [ commands ]
Creates number new turtles. New turtles start at position (0, 0), are created with the 14 primary colors, and have headings from 0 to 360,
evenly spaced.
If the create-ordered- form is used, the new turtles are created as members of the given breed.
If commands are supplied, the new turtles immediately run them. This is useful for giving the new turtles a different color, heading, or
whatever. (The new turtles are created all at once then run one at a time, in random order.)
cro 100 [ fd 10 ]
;; makes an evenly spaced circle
create--to
create--to
create--from
create--from
create--with
create--with
create-link-to
create-links-to
create-link-from
create-links-from
create-link-with
create-links-with
create--to turtle
create--to turtle [ commands ]
create--from turtle
create--from turtle [ commands ]
create--with turtle
create--with turtle [ commands ]
create--to turtleset
create--to turtleset [ commands ]
create--from turtleset
create--from turtleset [ commands ]
create--with turtleset
create--with turtleset [ commands ]
create-link-to turtle
create-link-to turtle [ commands ]
create-link-from turtle
create-link-from turtle [ commands ]
create-link-with turtle
create-link-with turtle [ commands ]
create-links-to turtleset
create-links-to turtleset [ commands ]
create-links-from turtleset
create-links-from turtleset [ commands ]
create-links-with turtleset
create-links-with turtleset [ commands ]
Since 4.0
Since 4.0
Since 4.0
Since 4.0
Since 4.0
Since 4.0
Used for creating breeded and unbreeded links between turtles.
create-link-with
create-link-from
creates an undirected link between the caller and agent. create-link-to creates a directed link from the caller to agent.
creates a directed link from agent to the caller.
When the plural form of the breed name is used, an agentset is expected instead of an agent and links are created between the caller and all
agents in the agentset.
The optional command block is the set of commands each newly formed link runs. (The links are created all at once then run one at a time, in
random order.)
A node cannot be linked to itself. Also, you cannot have more than one undirected link of the same breed between the same two nodes, nor
can you have more than one directed link of the same breed going in the same direction between two nodes.
If you try to create a link where one (of the same breed) already exists, nothing happens. If you try to create a link from a turtle to itself you get
a runtime error.
to setup
clear-all
create-turtles 5
;; turtle 1 creates links with all other turtles
;; the link between the turtle and itself is ignored
ask turtle 0 [ create-links-with other turtles ]
show count links ;; shows 4
;; this does nothing since the link already exists
ask turtle 0 [ create-link-with turtle 1 ]
show count links ;; shows 4 since the previous link already existed
ask turtle 2 [ create-link-with turtle 1 ]
show count links ;; shows 5
end
directed-link-breed [red-links red-link]
undirected-link-breed [blue-links blue-link]
to setup
clear-all
create-turtles 5
;; create links in both directions between turtle 0
;; and all other turtles
ask turtle 0 [ create-red-links-to other turtles ]
ask turtle 0 [ create-red-links-from other turtles ]
show count links ;; shows 8
;; now create undirected links between turtle 0 and other turtles
ask turtle 0 [ create-blue-links-with other turtles ]
show count links ;; shows 12
end
create-turtles
crt
Since 1.0
Since 1.0
create-turtles number
create-turtles number [ commands ]
create- number
create- number [ commands ]
Creates number new turtles at the origin. New turtles have random integer headings and the color is randomly selected from the 14 primary
colors.
If the create- form is used, the new turtles are created as members of the given breed.
If commands are supplied, the new turtles immediately run them. This is useful for giving the new turtles a different color, heading, or
whatever. (The new turtles are created all at once then run one at a time, in random order.)
crt 100 [ fd 10 ]
;; makes a randomly spaced circle
breed [canaries canary]
breed [snakes snake]
to setup
clear-all
create-canaries 50 [ set color yellow ]
create-snakes 50 [ set color green ]
end
See also hatch, sprout.
create-temporary-plot-pen
Since 1.1
create-temporary-plot-pen string
A new temporary plot pen with the given name is created in the current plot and set to be the current pen.
Few models will want to use this primitive, because all temporary pens disappear when clear-plot or clear-all-plots are called. The normal way
to make a pen is to make a permanent pen in the plot's Edit dialog.
If a pen with that name already exists in the current plot, no new pen is created, and the existing pen is set to the current pen.
The new temporary plot pen has the following initial settings:
Pen: down
Color: black
Mode: 0 (line mode)
Interval: 1
See: clear-plot, clear-all-plots, and set-current-plot-pen.
D
date-and-time
Since 3.0
date-and-time
Reports a string containing the current date and time. The format is shown below. All fields are fixed width, so they are always at the same
locations in the string. The potential resolution of the clock is milliseconds. (Whether you get resolution that high in practice may vary from
system to system, depending on the capabilities of the underlying Java Virtual Machine.)
show date-and-time
=> "01:19:36.685 PM 19-Sep-2002"
die
Since 1.0
die
The turtle or link dies.
if xcor > 20 [ die ]
;; all turtles with xcor greater than 20 die
ask links with [color = blue] [ die ]
;; all the blue links will die
A dead agent ceases to exist. The effects of this include:
The agent will not execute any further code. So if you write ask turtles [ die print "last words?" ] , no last words will be printed,
because the turtles are already dead before they have a chance to print anything.
The agent will disappear from any agentsets it was in, reducing the size of those agentsets by one.
Any variable that was storing the agent will now instead have nobody in it. So for example let x one-of turtles ask x [ die ] print x
prints nobody.
If the dead agent was a turtle, every link connected to it also dies.
If the observer was watching or following the agent, the observer's perspective resets, as if reset-perspective had been run.
See also: clear-turtles clear-links
diffuse
Since 1.0
diffuse patch-variable number
Tells each patch to give equal shares of (number * 100) percent of the value of patch-variable to its eight neighboring patches. number
should be between 0 and 1. Regardless of topology the sum of patch-variable will be conserved across the world. (If a patch has fewer than
eight neighbors, each neighbor still gets an eighth share; the patch keeps any leftover shares.)
Note that this is an observer command only, even though you might expect it to be a patch command. (The reason is that it acts on all the
patches at once -- patch commands act on individual patches.)
diffuse chemical 0.5
;; each patch diffuses 50% of its variable
;; chemical to its neighboring 8 patches. Thus,
;; each patch gets 1/8 of 50% of the chemical
;; from each neighboring patch.)
diffuse4
Since 1.0
diffuse4 patch-variable number
Like diffuse, but only diffuses to the four neighboring patches (to the north, south, east, and west), not to the diagonal neighbors.
diffuse4 chemical 0.5
;; each patch diffuses 50% of its variable
;; chemical to its neighboring 4 patches. Thus,
;; each patch gets 1/4 of 50% of the chemical
;; from each neighboring patch.)
directed-link-breed
directed-link-breed []
This keyword, like the globals and breeds keywords, can only be used at the beginning of the Code tab, before any procedure definitions. It
defines a directed link breed. Links of a particular breed are always all directed or all undirected The first input defines the name of the
agentset associated with the link breed. The second input defines the name of a single member of the breed. Directed links can be created
using create-link(s)-to, and create-link(s)-from, but not create-link(s)-with
Any link of the given link breed:
is part of the agentset named by the link breed name
has its built-in variable breed set to that agentset
is directed or undirected as declared by the keyword
Most often, the agentset is used in conjunction with ask to give commands to only the links of a particular breed.
directed-link-breed [streets street]
directed-link-breed [highways highway]
to setup
clear-all
crt 2
;; create a link from turtle 0 to turtle 1
ask turtle 0 [ create-street-to turtle 1 ]
;; create a link from turtle 1 to turtle 0
ask turtle 0 [ create-highway-from turtle 1 ]
end
ask turtle 0 [ show one-of my-in-links ]
;; prints (street 0 1)
ask turtle 0 [ show one-of my-out-links ]
;; prints (highway 1 0)
See also breed, undirected-link-breed
display
Since 1.0
display
Causes the view to be updated immediately. (Exception: if the user is using the speed slider to fast-forward the model, then the update may
be skipped.)
Also undoes the effect of the no-display command, so that if view updates were suspended by that command, they will resume.
no-display
ask turtles [ jump 10 set color blue set size 5 ]
display
;; turtles move, change color, and grow, with none of
;; their intermediate states visible to the user, only
;; their final state
Even if no-display was not used, "display" can still be useful, because ordinarily NetLogo is free to skip some view updates, so that fewer
total updates take place, so that models run faster. This command lets you force a view update, so whatever changes have taken place in the
world are visible to the user.
ask turtles [ set color red ]
display
ask turtles [ set color blue]
;; turtles turn red, then blue; use of "display" forces
;; red turtles to appear briefly
Note that display and no-display operate independently of the switch in the view control strip that freezes the view.
See also no-display.
distance
Since 1.0
distance agent
Reports the distance from this agent to the given turtle or patch.
The distance to or a from a patch is measured from the center of the patch. Turtles and patches use the wrapped distance (around the edges
of the world) if wrapping is allowed by the topology and the wrapped distance is shorter.
ask turtles [ show max-one-of turtles [distance myself] ]
;; each turtle prints the turtle farthest from itself
distancexy
Since 1.0
distancexy x y
Reports the distance from this agent to the point (x, y).
The distance from a patch is measured from the center of the patch. Turtles and patches use the wrapped distance (around the edges of the
world) if wrapping is allowed by the topology and the wrapped distance is shorter.
if (distancexy 0 0) > 10
[ set color green ]
;; all turtles more than 10 units from
;; the center of the world turn green.
downhill
downhill4
Since 1.0
Since 1.0
downhill patch-variable
downhill4 patch-variable
Moves the turtle to the neighboring patch with the lowest value for patch-variable. If no neighboring patch has a smaller value than the
current patch, the turtle stays put. If there are multiple patches with the same lowest value, the turtle picks one randomly. Non-numeric
values are ignored.
downhill considers the eight neighboring patches; downhill4 only considers the four neighbors.
Equivalent to the following code (assumes variable values are numeric):
move-to patch-here ;; go to patch center
let p min-one-of neighbors [patch-variable]
if [patch-variable] of p < patch-variable [
face p
move-to p
]
;; or neighbors4
Note that the turtle always ends up on a patch center and has a heading that is a multiple of 45 (downhill) or 90 (downhill4).
See also uphill, uphill4.
dx
dy
Since 1.0
Since 1.0
dx
dy
Reports the x-increment or y-increment (the amount by which the turtle's xcor or ycor would change) if the turtle were to take one step
forward in its current heading.
Note: dx is simply the sine of the turtle's heading, and dy is simply the cosine. (If this is the reverse of what you expected, it's because in
NetLogo a heading of 0 is north and 90 is east, which is the reverse of how angles are usually defined in geometry.)
Note: In earlier versions of NetLogo, these primitives were used in many situations where the new patch-ahead primitive is now more
appropriate.
E
empty?
Since 1.0
empty? list
empty? string
Reports true if the given list or string is empty, false otherwise.
Note: the empty list is written []. The empty string is written "".
end
end
Used to conclude a procedure. See to and to-report.
end1
Since 4.0
end1
This is a built-in link variable. It indicates the first endpoint (turtle) of a link. For directed links this will always be the source for undirected links
it will always be the turtle with the lower who number. You cannot set end1.
crt 2
ask turtle 0
[ create-link-to turtle 1 ]
ask links
[ show end1 ] ;; shows turtle 0
end2
Since 4.0
end2
This is a built-in link variable. It indicates the second endpoint (turtle) of a link. For directed links this will always be the destination for
undirected links it will always be the turtle with the higher who number. You cannot set end2.
crt 2
ask turtle 1
[ create-link-with turtle 0 ]
ask links
[ show end2 ] ;; shows turtle 1
error
Since 5.0
error value
Causes a runtime error to occur.
The given value is converted to a string (if it isn't one already) and used as the error message.
See also error-message, carefully.
error-message
Since 2.1
error-message
Reports a string describing the error that was suppressed by carefully.
This reporter can only be used in the second block of a carefully command.
See also error, carefully.
every
Since 1.0
every number [ commands ]
Runs the given commands only if it's been more than number seconds since the last time this agent ran them in this context. Otherwise, the
commands are skipped.
By itself, every doesn't make commands run over and over again. You need to use every inside a loop, or inside a forever button, if you want
the commands run over and over again. every only limits how often the commands run.
Above, "in this context" means during the same ask (or button press or command typed in the Command Center). So it doesn't make sense
to write ask turtles [ every 0.5 [ ... ] ], because when the ask finishes the turtles will all discard their timers for the "every". The correct
usage is shown below.
every 0.5 [ ask turtles [ fd 1 ] ]
;; twice a second the turtles will move forward 1
every 2 [ set index index + 1 ]
;; every 2 seconds index is incremented
See also wait.
exp
Since 1.0
exp number
Reports the value of e raised to the number power.
Note: This is the same as e ^ number.
export-view
export-interface
export-output
export-plot
export-all-plots
export-world
Since 3.0
Since 2.0
Since 1.0
Since 1.0
Since 1.2.1
Since 1.0
export-view filename
export-interface filename
export-output filename
export-plot plotname filename
export-all-plots filename
export-world filename
export-view writes the current contents of the current view to an external file given by the string filename. The file is saved in PNG (Portable
Network Graphics) format, so it is recommended to supply a filename ending in ".png".
export-interface is similar, but for the whole interface tab.
Note that export-view still works when running NetLogo in headless mode, but export-interface doesn't.
export-output writes the contents of the model's output area to an external file given by the string filename. (If the model does not have a
separate output area, the output portion of the Command Center is used.)
export-plot writes the x and y values of all points plotted by all the plot pens in the plot given by the string plotname to an external file given by
the string filename. If a pen is in bar mode (mode 0) and the y value of the point plotted is greater than 0, the upper-left corner point of the bar
will be exported. If the y value is less than 0, then the lower-left corner point of the bar will be exported.
export-all-plots writes every plot in the current model to an external file given by the string filename. Each plot is identical in format to the
output of export-plot.
export-world writes the values of all variables, both built-in and user-defined, including all observer, turtle, and patch variables, the drawing,
the contents of the output area if one exists, the contents of any plots and the state of the random number generator, to an external file given
by the string filename. (The result file can be read back into NetLogo with the import-world primitive.) export-world does not save the state of
open files.
export-plot, export-all-plots and export-world save files in in plain-text, "comma-separated values" (.csv) format. CSV files can be read by
most popular spreadsheet and database programs as well as any text editor.
If you wish to export to a file in a location other than the model's location, you should include the full path to the file you wish to export. (Use
the forward-slash "/" as the folder separator.)
Note that the functionality of these primitives is also available directly from NetLogo's File menu.
export-world "fire.csv"
;; exports the state of the model to the file fire.csv
;; located in the NetLogo folder
export-plot "Temperature" "c:/My Documents/plot.csv"
;; exports the plot named
;; "Temperature" to the file plot.csv located in
;; the C:\My Documents folder
export-all-plots "c:/My Documents/plots.csv"
;; exports all plots to the file plots.csv
;; located in the C:\My Documents folder
If the file already exists, it is overwritten. To avoid this you may wish to use some method of generating fresh names. Examples:
export-world user-new-file
export-world (word "results " date-and-time ".csv") ;; Colon characters in the time cause errors on Windows
export-world (word "results " random-float 1.0 ".csv")
extensions
extensions [name ...]
Allows the model to use primitives from the extensions with the given names. See the Extensions guide for more information.
extract-hsb
Since 1.0
extract-hsb color
Reports a list of three values, the first (hue) in the range of 0 to 360, the second and third (brightness and saturation) in the range of in the
range 0 to 100, of the given NetLogo color in the range 0 to 140, not including 140 itself.
show extract-hsb red
=> [3.103 80.93 84.314]
show extract-hsb cyan
=> [180 57.143 76.863]
See also approximate-hsb, approximate-rgb, extract-rgb.
extract-rgb
Since 1.0
extract-rgb color
Reports a list of three values in the range 0 to 255 representing the levels of red, green, and blue, respectively, of the given NetLogo color in
the range 0 to 140, not including 140 itself.
show extract-rgb red
=> [215 50 41]
show extract-rgb cyan
=> [84 196 196]
See also approximate-rgb, approximate-hsb, extract-hsb.
F
face
Since 3.0
face agent
Set the caller's heading towards agent.
If wrapping is allowed by the topology and the wrapped distance (around the edges of the world) is shorter, face will use the wrapped path.
If the caller and the agent are at the exact same position, the caller's heading won't change.
facexy
Since 3.0
facexy x y
Set the caller's heading towards the point (x,y).
If wrapping is allowed by the topology and the wrapped distance (around the edges of the world) is shorter and wrapping is allowed, facexy
will use the wrapped path.
If the caller is on the point (x,y), the caller's heading won't change.
file-at-end?
Since 2.0
file-at-end?
Reports true when there are no more characters left to read in from the current file (that was opened previously with file-open). Otherwise,
reports false.
file-open "my-file.txt"
print file-at-end?
=> false ;; Can still read in more characters
print file-read-line
=> This is the last line in file
print file-at-end?
=> true ;; We reached the end of the file
See also file-open, file-close-all.
file-close
Since 2.0
file-close
Closes a file that has been opened previously with file-open.
Note that this and file-close-all are the only ways to restart to the beginning of an opened file or to switch between file modes.
If no file is open, does nothing.
See also file-close-all, file-open.
file-close-all
Since 2.0
file-close-all
Closes all files (if any) that have been opened previously with file-open.
See also file-close, file-open.
file-delete
Since 2.0
file-delete string
Deletes the file specified as string
string must be an existing file with writable permission by the user. Also, the file cannot be open. Use the command file-close to close an
opened file before deletion.
Note that the string can either be a file name or an absolute file path. If it is a file name, it looks in whatever the current directory is. This can
be changed using the command set-current-directory. It is defaulted to the model's directory.
file-exists?
Since 2.0
file-exists? string
Reports true if string is the name of an existing file on the system. Otherwise it reports false.
Note that the string can either be a file name or an absolute file path. If it is a file name, it looks in whatever the current directory is. This can
be changed using the command set-current-directory. It defaults to to the model's directory.
file-flush
Since 4.0
file-flush
Forces file updates to be written to disk. When you use file-write or other output commands, the values may not be immediately written to
disk. This improves the performance of the file output commands. Closing a file ensures that all output is written to disk.
Sometimes you need to ensure that data is written to disk without closing the file. For example, you could be using a file to communicate with
another program on your machine and want the other program to be able to see the output immediately.
file-open
file-open string
Since 2.0
This command will interpret string as a path name to a file and open the file. You may then use the reporters file-read, file-read-line, and fileread-characters to read in from the file, or file-write, file-print, file-type, or file-show to write out to the file.
Note that you can only open a file for reading or writing but not both. The next file i/o primitive you use after this command dictates which
mode the file is opened in. To switch modes, you need to close the file using file-close.
Also, the file must already exist if opening a file in reading mode.
When opening a file in writing mode, all new data will be appended to the end of the original file. If there is no original file, a new blank file will
be created in its place. (You must have write permission in the file's directory.) (If you don't want to append, but want to replace the file's
existing contents, use file-delete to delete it first, perhaps inside a carefully if you're not sure whether it already exists.)
Note that the string can either be a file name or an absolute file path. If it is a file name, it looks in whatever the current directory is. This can
be changed using the command set-current-directory. It is defaulted to the model's directory.
file-open "my-file-in.txt"
print file-read-line
=> First line in file ;; File is in reading mode
file-open "C:\\NetLogo\\my-file-out.txt"
;; assuming Windows machine
file-print "Hello World" ;; File is in writing mode
Opening a file does not close previously opened files. You can use file-open to switch back and forth between multiple open files.
See also file-close See also file-close-all.
file-print
Since 2.0
file-print value
Prints value to an opened file, followed by a carriage return.
This agent is not printed before the value, unlike file-show.
Note that this command is the file i/o equivalent of print, and file-open needs to be called before this command can be used.
See also file-show, file-type, and file-write.
file-read
Since 2.0
file-read
This reporter will read in the next constant from the opened file and interpret it as if it had been typed in the Command Center. It reports the
resulting value. The result may be a number, list, string, boolean, or the special value nobody.
Whitespace separates the constants. Each call to file-read will skip past both leading and trailing whitespace.
Note that strings need to have quotes around them. Use the command file-write to have quotes included.
Also note that the file-open command must be called before this reporter can be used, and there must be data remaining in the file. Use the
reporter file-at-end? to determine if you are at the end of the file.
file-open "my-file.data"
print file-read + 5
;; Next value is the number 1
=> 6
print length file-read
;; Next value is the list [1 2 3 4]
=> 4
See also file-open and file-write.
file-read-characters
Since 2.0
file-read-characters number
Reports the given number of characters from an opened file as a string. If there are fewer than that many characters left, it will report all of the
remaining characters.
Note that it will return every character including newlines and spaces.
Also note that the file-open command must be called before this reporter can be used, and there must be data remaining in the file. Use the
reporter file-at-end? to determine if you are at the end of the file.
file-open "my-file.txt"
print file-read-characters 5
;; Current line in file is "Hello World"
=> Hello
See also file-open.
file-read-line
file-read-line
Since 2.0
Reads the next line in the file and reports it as a string. It determines the end of the file by a carriage return, an end of file character or both in
a row. It does not return the line terminator characters.
Also note that the file-open command must be called before this reporter can be used, and there must be data remaining in the file. Use the
reporter file-at-end? to determine if you are at the end of the file.
file-open "my-file.txt"
print file-read-line
=> Hello World
See also file-open.
file-show
Since 2.0
file-show value
Prints value to an opened file, preceded by this agent agent, and followed by a carriage return. (This agent is included to help you keep track
of what agents are producing which lines of output.) Also, all strings have their quotes included similar to file-write.
Note that this command is the file i/o equivalent of show, and file-open needs to be called before this command can be used.
See also file-print, file-type, and file-write.
file-type
Since 2.0
file-type value
Prints value to an opened file, not followed by a carriage return (unlike file-print and file-show). The lack of a carriage return allows you to print
several values on the same line.
This agent is not printed before the value. unlike file-show.
Note that this command is the file i/o equivalent of type, and file-open needs to be called before this command can be used.
See also file-print, file-show, and file-write.
file-write
Since 2.0
file-write value
This command will output value, which can be a number, string, list, boolean, or nobody to an opened file, not followed by a carriage return
(unlike file-print and file-show).
This agent is not printed before the value, unlike file-show. Its output also includes quotes around strings and is prepended with a space. It
will output the value in such a manner that file-read will be able to interpret it.
Note that this command is the file i/o equivalent of write, and file-open needs to be called before this command can be used.
file-open "locations.txt"
ask turtles
[ file-write xcor file-write ycor ]
See also file-print, file-show, and file-type.
filter
Since 1.3
filter reporter list
Reports a list containing only those items of list for which the reporter reports true -- in other words, the items satisfying the given condition.
reporter may be an anonymous reporter or the name of a reporter.
show filter is-number? [1 "2" 3]
=> [1 3]
show filter [ i -> i < 3 ] [1 3 2]
=> [1 2]
show filter [ s -> first s != "t" ] ["hi" "there" "everyone"]
=> ["hi" "everyone"]
See also map, reduce, -> (anonymous procedure).
first
Since 1.0
first list
first string
On a list, reports the first (0th) item in the list.
On a string, reports a one-character string containing only the first character of the original string.
floor
Since 1.0
floor number
Reports the largest integer less than or equal to number.
show floor 4.5
=> 4
show floor -4.5
=> -5
See also ceiling, round, precision.
follow
Since 3.0
follow turtle
Similar to ride, but, in the 3D view, the observer's vantage point is behind and above turtle.
The observer may only watch or follow a single subject. Calling follow will alter the highlight created by prior calls to watch and watch-me ,
highlighting the followed turtle instead.
See also follow-me, ride, reset-perspective, watch, subject.
follow-me
Since 3.0
follow-me
Asks the observer to follow this turtle.
The observer may only watch or follow a single subject. Calling follow-me will remove the highlight created by prior calls to watch and watchme , highlighting this turtle instead.
See also follow.
foreach
Since 1.3
foreach list command
(foreach list1 ... command)
With a single list, runs the command for each item of list. command may be the name of a command, or an anonymous command created
with ->.
foreach [1.1 2.2 2.6] show
=> 1.1
=> 2.2
=> 2.6
foreach [1.1 2.2 2.6] [ x -> show (word x " -> " round x) ]
=> 1.1 -> 1
=> 2.2 -> 2
=> 2.6 -> 3
With multiple lists, runs command for each group of items from each list. So, they are run once for the first items, once for the second items,
and so on. All the lists must be the same length.
Some examples make this clearer:
(foreach [1 2 3] [2 4 6]
[ [a b] -> show word "the sum is: " (a + b) ])
=> "the sum is: 3"
=> "the sum is: 6"
=> "the sum is: 9"
(foreach list (turtle 1) (turtle 2) [3 4]
[ [the-turtle num-steps] -> ask the-turtle [ fd num-steps ] ])
;; turtle 1 moves forward 3 patches
;; turtle 2 moves forward 4 patches
See also map, -> (anonymous procedure).
forward
fd
Since 1.0
Since 1.0
forward number
The turtle moves forward by number steps, one step at a time. (If number is negative, the turtle moves backward.)
fd 10
is equivalent to repeat 10 [ jump 1 ] . fd 10.5 is equivalent to repeat 10 [ jump 1 ] jump 0.5.
If the turtle cannot move forward number steps because it is not permitted by the current topology the turtle will complete as many steps of 1
as it can, then stop.
See also jump, can-move?.
fput
Since 1.0
fput item list
Adds item to the beginning of a list and reports the new list.
;; suppose mylist is [5 7 10]
set mylist fput 2 mylist
;; mylist is now [2 5 7 10]
G
globals
globals [var1 ...]
This keyword, like the breed, -own, patches-own, and turtles-own keywords, can only be used at the beginning of a program, before
any function definitions. It defines new global variables. Global variables are "global" because they are accessible by all agents and can be
used anywhere in a model.
Most often, globals is used to define variables or constants that need to be used in many parts of the program.
H
hatch
Since 1.0
hatch number [ commands ]
hatch- number [ commands ]
This turtle creates number new turtles. Each new turtle inherits of all its variables, including its location, from its parent. (Exceptions: each
new turtle will have a new who number, and it may be of a different breed than its parent if the hatch- form is used.)
The new turtles then run commands. You can use the commands to give the new turtles different colors, headings, locations, or whatever.
(The new turtles are created all at once, then run one at a time, in random order.)
If the hatch- form is used, the new turtles are created as members of the given breed. Otherwise, the new turtles are the same
breed as their parent.
hatch 1 [ lt 45 fd 1 ]
;; this turtle creates one new turtle,
;; and the child turns and moves away
hatch-sheep 1 [ set color black ]
;; this turtle creates a new turtle
;; of the sheep breed
See also create-turtles, sprout.
heading
heading
This is a built-in turtle variable. It indicates the direction the turtle is facing. This is a number greater than or equal to 0 and less than 360. 0 is
north, 90 is east, and so on. You can set this variable to make a turtle turn.
See also right, left, dx, dy.
Example:
set heading 45
;; turtle is now facing northeast
set heading heading + 10 ;; same effect as "rt 10"
hidden?
hidden?
This is a built-in turtle or link variable. It holds a boolean (true or false) value indicating whether the turtle or link is currently hidden (i.e.,
invisible). You can set this variable to make a turtle or link disappear or reappear.
See also hide-turtle, show-turtle, hide-link, show-link
Example:
set hidden? not hidden?
;; if turtle was showing, it hides, and if it was hiding,
;; it reappears
hide-link
Since 4.0
hide-link
The link makes itself invisible.
Note: This command is equivalent to setting the link variable "hidden?" to true.
See also show-link.
hide-turtle
ht
Since 1.0
Since 1.0
hide-turtle
The turtle makes itself invisible.
Note: This command is equivalent to setting the turtle variable "hidden?" to true.
See also show-turtle.
histogram
Since 1.0
histogram list
Histograms the values in the given list
Draws a histogram showing the frequency distribution of the values in the list. The heights of the bars in the histogram represent the
numbers of values in each subrange.
Before the histogram is drawn, first any previous points drawn by the current plot pen are removed.
Any non-numeric values in the list are ignored.
The histogram is drawn on the current plot using the current plot pen and pen color. Auto scaling does not affect a histogram's horizontal
range, so set-plot-x-range should be used to control the range, and the pen interval can then be set (either directly with set-plot-pen-interval,
or indirectly via set-histogram-num-bars) to control how many bars that range is split up into.
Be sure that if you want the histogram drawn with bars that the current pen is in bar mode (mode 1).
For histogramming purposes the plot's X range is not considered to include the maximum X value. Values equal to the maximum X will fall
outside of the histogram's range.
histogram [color] of turtles
;; draws a histogram showing how many turtles there are
;; of each color
home
Since 1.0
home
This turtle moves to the origin (0,0). Equivalent to setxy 0 0.
hsb
Since 1.0
hsb hue saturation brightness
Reports a RGB list when given three numbers describing an HSB color. Hue, saturation, and brightness are integers in the range 0-360, 0100, 0-100 respectively. The RGB list contains three integers in the range of 0-255.
See also rgb
hubnet-broadcast
Since 1.1
hubnet-broadcast tag-name value
This broadcasts value from NetLogo to the interface element with the name tag-name on the clients.
See the HubNet Authoring Guide for details and instructions.
hubnet-broadcast-clear-output
hubnet-broadcast-clear-output
This clears all messages printed to the text area on every client.
See also: hubnet-broadcast-message, hubnet-send-clear-output
Since 4.1
hubnet-broadcast-message
Since 4.1
hubnet-broadcast-message value
This prints the value in the text area on each client. This is the same functionality as the "Broadcast Message" button in the HubNet Control
Center.
See also: hubnet-send-message
hubnet-clear-override
hubnet-clear-overrides
Since 4.1
Since 4.1
hubnet-clear-override client agent-or-set variable-name
hubnet-clear-overrides client
Remove overrides from the override list on client. hubnet-clear-override removes only the override for the specified variable for the specified
agent or agentset. hubnet-clear-overrides removes all overrides from the specified client.
See also: hubnet-send-override
hubnet-clients-list
Since 5.0
hubnet-clients-list
Reports a list containing the names of all the clients currently connected to the HubNet server.
hubnet-enter-message?
Since 1.2.1
hubnet-enter-message?
Reports true if a new client just entered the simulation. Reports false otherwise. hubnet-message-source will contain the user name of the
client that just logged on.
See the HubNet Authoring Guide for details and instructions.
hubnet-exit-message?
Since 1.2.1
hubnet-exit-message?
Reports true if a client just exited the simulation. Reports false otherwise. hubnet-message-source will contain the user name of the client that
just logged off.
See the HubNet Authoring Guide for details and instructions.
hubnet-fetch-message
Since 1.1
hubnet-fetch-message
If there is any new data sent by the clients, this retrieves the next piece of data, so that it can be accessed by hubnet-message, hubnetmessage-source, and hubnet-message-tag. This will cause an error if there is no new data from the clients.
See the HubNet Authoring Guide for details.
hubnet-kick-client
Since 5.0
hubnet-kick-client client-name
Kicks the client with the given client-name. This is equivalent to clicking the client name in the HubNet Control Center and pressing the Kick
button.
hubnet-kick-all-clients
Since 5.0
hubnet-kick-all-clients
Kicks out all currently connected HubNet clients. This is equivalent to selecting all clients in the HubNet Control Center and pressing the Kick
button.
hubnet-message
Since 1.1
hubnet-message
Reports the message retrieved by hubnet-fetch-message.
See the HubNet Authoring Guide for details.
hubnet-message-source
Since 1.1
hubnet-message-source
Reports the name of the client that sent the message retrieved by hubnet-fetch-message.
See the HubNet Authoring Guide for details.
hubnet-message-tag
Since 1.1
hubnet-message-tag
Reports the tag that is associated with the data that was retrieved by hubnet-fetch-message. The tag will be one of the Display Names of the
interface elements in the client interface.
See the HubNet Authoring Guide for details.
hubnet-message-waiting?
Since 1.1
hubnet-message-waiting?
This looks for a new message sent by the clients. It reports true if there is one, and false if there is not.
See the HubNet Authoring Guide for details.
hubnet-reset
Since 1.1
hubnet-reset
Starts up the HubNet system. HubNet must be started to use any of the other hubnet primitives.
See the HubNet Authoring Guide for details.
hubnet-reset-perspective
Since 4.1
hubnet-reset-perspective tag-name
Clears watch or follow sent directly to the client. The view perspective will revert to the server perspective.
See also: hubnet-send-watch hubnet-send-follow
hubnet-send
Since 1.1
hubnet-send string tag-name value
hubnet-send list-of-strings tag-name value
For a string, this sends value from NetLogo to the tag tag-name on the client that has string for its user name.
For a list-of-strings, this sends value from NetLogo to the tag tag-name on all the clients that have a user name that is in the list-of-strings.
Sending a message to a non-existent client, using hubnet-send, generates a hubnet-exit-message .
See the HubNet Authoring Guide for details.
hubnet-send-clear-output
Since 4.1
hubnet-send-clear-output string
hubnet-send-clear-output list-of-strings
This clears all messages printed to the text area on the given client or clients (specified in the string or list-of-strings.
See also: hubnet-send-message, hubnet-broadcast-clear-output
hubnet-send-follow
Since 4.1
hubnet-send-follow client-name agent radius
Tells the client associated with client-name to follow agent showing a radius sized Moore neighborhood around the agent.
A client may only watch or follow a single subject. Calling hubnet-send-follow will alter the highlight created by prior calls to hubnet-sendwatch, highlighting the followed agent instead.
See also: hubnet-send-watch, hubnet-reset-perspective
hubnet-send-message
hubnet-send-message string value
Since 4.1
This prints value in the text area on the client specified by string.
See also: hubnet-broadcast-message
hubnet-send-override
Since 4.1
hubnet-send-override client-name agent-or-set variable-name
[ reporter ]
Evaluates reporter for the agent or agentset indicated then sends the values to the client to "override" the value of variable-name only on
client-name. This is used to change the appearance of agents in the client view, hence, only built-in variables that affect the appearance of
the agent may be selected. For example, you can override the color variable of a turtle:
ask turtles [ hubnet-send-override client-name self "color" [ red ] ]
In this example assume that there is a turtles-own variable client-name which is associated with a logged in client, and all the turtles are blue.
This code makes the turtle associated with each client appear red in his or her own view but not on anyone else's or on the server.
See also: hubnet-clear-overrides
hubnet-send-watch
Since 4.1
hubnet-send-watch client-name agent
Tells the client associated with client-name to watch agent.
A client may only watch or follow a single subject. Calling hubnet-send-watch will undo perspective changes caused by prior calls to hubnetsend-follow.
See also: hubnet-send-follow, hubnet-reset-perspective
I
if
Since 1.0
if condition [ commands ]
Reporter must report a boolean (true or false) value.
If condition reports true, runs commands.
The reporter may report a different value for different agents, so some agents may run commands and others don't.
if xcor > 0[ set color blue ]
;; turtles in the right half of the world
;; turn blue
See also ifelse, ifelse-value.
ifelse
Since 1.0
ifelse reporter [ commands1 ] [ commands2 ]
Reporter must report a boolean (true or false) value.
If reporter reports true, runs commands1.
If reporter reports false, runs commands2.
The reporter may report a different value for different agents, so some agents may run commands1 while others run commands2.
ask patches
[ ifelse pxcor > 0
[ set pcolor blue ]
[ set pcolor red ] ]
;; the left half of the world turns red and
;; the right half turns blue
See also if, ifelse-value.
ifelse-value
ifelse-value reporter [reporter1] [reporter2]
Reporter must report a boolean (true or false) value.
If reporter reports true, the result is the value of reporter1.
If reporter reports false, the result is the value of reporter2.
This can be used when a conditional is needed in the context of a reporter, where commands (such as ifelse) are not allowed.
Since 2.0
ask patches [
set pcolor ifelse-value (pxcor > 0) [blue] [red]
]
;; the left half of the world turns red and
;; the right half turns blue
show n-values 10 [ifelse-value (? < 5) [0] [1]]
=> [0 0 0 0 0 1 1 1 1 1]
show reduce [ [a b] -> ifelse-value (a > b) [a] [b] ]
[1 3 2 5 3 8 3 2 1]
=> 8
See also if, ifelse.
import-drawing
Since 3.0
import-drawing filename
Reads an image file into the drawing, scaling it to the size of the world, while retaining the original aspect ratio of the image. The image is
centered in the drawing. The old drawing is not cleared first.
Agents cannot sense the drawing, so they cannot interact with or process images imported by import-drawing. If you need agents to sense an
image, use import-pcolors or import-pcolors-rgb.
The following image file formats are supported: BMP, JPG, GIF, and PNG. If the image format supports transparency (alpha), that
information will be imported as well.
import-pcolors
Since 3.0
import-pcolors filename
Reads an image file, scales it to the same dimensions as the patch grid while maintaining the original aspect ratio of the image, and transfers
the resulting pixel colors to the patches. The image is centered in the patch grid. The resulting patch colors may be distorted, since the
NetLogo color space does not include all possible colors. (See the Color section of the Programming Guide.) import-pcolors may be slow for
some images, particularly when you have many patches and a large image with many different colors.
Since import-pcolors sets the pcolor of patches, agents can sense the image. This is useful if agents need to analyze, process, or otherwise
interact with the image. If you want to simply display a static backdrop, without color distortion, see import-drawing.
The following image file formats are supported: BMP, JPG, GIF, and PNG. If the image format supports transparency (alpha), then all fully
transparent pixels will be ignored. (Partially transparent pixels will be treated as opaque.)
import-pcolors-rgb
Since 4.0
import-pcolors-rgb filename
Reads an image file, scales it to the same dimensions as the patch grid while maintaining the original aspect ratio of the image, and transfers
the resulting pixel colors to the patches. The image is centered in the patch grid. Unlike import-pcolors the exact colors in the original image
are retained. The pcolor variable of all the patches will be an RGB list rather than an (approximated) NetLogo color.
The following image file formats are supported: BMP, JPG, GIF, and PNG. If the image format supports transparency (alpha), then all fully
transparent pixels will be ignored. (Partially transparent pixels will be treated as opaque.)
import-world
Since 1.0
import-world filename
Reads the values of all variables for a model, both built-in and user-defined, including all observer, turtle, and patch variables, from an
external file named by the given string. The file should be in the format used by the export-world primitive.
Note that the functionality of this primitive is also directly available from NetLogo's File menu.
When using import-world, to avoid errors, perform these steps in the following order:
1.
2.
3.
4.
5.
Open the model from which you created the export file.
Press the Setup button, to get the model in a state from which it can be run.
Import the file.
Re-open any files that the model had opened with the file-open command.
If you want, press Go button to continue running the model from the point where it left off.
If you wish to import a file from a location other than the model's location, you may include the full path to the file you wish to import. See
export-world for an example.
in-cone
Since 3.0
agentset in-cone distance angle
This reporter lets you give a turtle a "cone of vision" in front of itself. The cone is defined by the two inputs, the vision distance (radius) and
the viewing angle. The viewing angle may range from 0 to 360 and is centered around the turtle's current heading. (If the angle is 360, then
in-cone is equivalent to in-radius.)
in-cone reports an agentset that includes only those agents from the original agentset that fall in the cone. (This can include the agent itself.)
The distance to a patch is measured from the center of the patch.
ask turtles
[ ask patches in-cone 3 60
[ set pcolor red ] ]
;; each turtle makes a red "splotch" of patches in a 60 degree
;; cone of radius 3 ahead of itself
in--neighbor?
in-link-neighbor?
Since 4.0
in--neighbor? agent
in-link-neighbor? turtle
Reports true if there is a directed link going from turtle to the caller or an undirected link connecting turtle to the caller. You can think of this as
"is there a link I can use to get from turtle to the caller?"
crt 2
ask turtle 0 [
create-link-to turtle 1
show in-link-neighbor? turtle 1
show out-link-neighbor? turtle 1
]
ask turtle 1 [
show in-link-neighbor? turtle 0
show out-link-neighbor? turtle 0
]
;; prints false
;; prints true
;; prints true
;; prints false
in--neighbors
in-link-neighbors
Since 4.0
in--neighbors
in-link-neighbors
Reports the agentset of all the turtles that have directed links coming from them to the caller as well as all turtles that have an undirected link
connecting them with the caller. You can think of this as "all the turtles that can get to the caller using a link."
crt 4
ask turtle 0 [ create-links-to other turtles ]
ask turtle 1 [ ask in-link-neighbors [ set color blue ] ] ;; turtle 0 turns blue
in--from
in-link-from
Since 4.0
in--from turtle
in-link-from turtle
Reports a directed link from turtle to the caller or an undirected link connecting the two. If no link exists then it reports nobody. If more than
one such link exists, reports a random one. You can think of this as "give me a link that I can use to travel from turtle to the caller."
crt
ask
ask
ask
2
turtle 0 [ create-link-to turtle 1 ]
turtle 1 [ show in-link-from turtle 0 ] ;; shows link 0 1
turtle 0 [ show in-link-from turtle 1 ] ;; shows nobody
See also: out-link-to link-with
__includes
Since 4.0
__includes [ filename ... ]
Causes external NetLogo source files (with the .nls suffix) to be included in this model. Included files may contain breed, variable, and
procedure definitions. __includes can only be used once per file.
in-radius
Since 1.0
agentset in-radius number
Reports an agentset that includes only those agents from the original agentset whose distance from the caller is less than or equal to
number. (This can include the agent itself.)
The distance to or a from a patch is measured from the center of the patch.
ask turtles
[ ask patches in-radius 3
[ set pcolor red ] ]
;; each turtle makes a red "splotch" around itself
inspect
Since 1.1
inspect agent
Opens an agent monitor for the given agent (turtle or patch).
inspect patch 2 4
;; an agent monitor opens for that patch
inspect one-of sheep
;; an agent monitor opens for a random turtle from
;; the "sheep" breed
See stop-inspecting and stop-inspecting-dead-agents
int
Since 1.0
int number
Reports the integer part of number -- any fractional part is discarded.
show int 4.7
=> 4
show int -3.5
=> -3
is-agent?
is-agentset?
is-anonymous-command?
is-anonymous-reporter?
is-boolean?
is-directed-link?
is-link?
is-link-set?
is-list?
is-number?
is-patch?
is-patch-set?
is-string?
is-turtle?
is-turtle-set?
is-undirected-link?
Since 1.2.1
Since 1.2.1
Since 6.0
Since 6.0
Since 1.2.1
Since 4.0
Since 4.0
Since 4.0
Since 1.0
Since 1.2.1
Since 1.2.1
Since 4.0
Since 1.0
Since 1.2.1
Since 4.0
Since 4.0
is-agent? value
is-agentset? value
is-anonymous-command? value
is-anonymous-reporter? value
is-boolean? value
is-? value
is-? value
is-directed-link? value
is-link? value
is-link-set? value
is-list? value
is-number? value
is-patch? value
is-patch-set? value
is-string? value
is-turtle? value
is-turtle-set? value
is-undirected-link? value
Reports true if value is of the given type, false otherwise.
item
item index list
item index string
On lists, reports the value of the item in the given list with the given index.
On strings, reports the character in the given string at the given index.
Note that the indices begin from 0, not 1. (The first item is item 0, the second item is item 1, and so on.)
Since 1.0
;; suppose mylist is [2 4 6 8 10]
show item 2 mylist
=> 6
show item 3 "my-shoe"
=> "s"
J
jump
Since 1.0
jump number
The turtle moves forward by number units all at once (rather than one step at a time as with the forward command).
If the turtle cannot jump number units because it is not permitted by the current topology the turtle does not move at all.
See also forward, can-move?.
L
label
label
This is a built-in turtle or link variable. It may hold a value of any type. The turtle or link appears in the view with the given value "attached" to
it as text. You can set this variable to add, change, or remove a turtle or link's label.
See also label-color, plabel, plabel-color.
Example:
ask turtles [ set label who ]
;; all the turtles now are labeled with their
;; who numbers
ask turtles [ set label "" ]
;; all turtles now are not labeled
label-color
label-color
This is a built-in turtle or link variable. It holds a number greater than or equal to 0 and less than 140. This number determines what color the
turtle or link's label appears in (if it has a label). You can set this variable to change the color of a turtle or link's label.
See also label, plabel, plabel-color.
Example:
ask turtles [ set label-color red ]
;; all the turtles now have red labels
last
Since 1.0
last list
last string
On a list, reports the last item in the list.
On a string, reports a one-character string containing only the last character of the original string.
layout-circle
Since 4.0
layout-circle agentset radius
layout-circle list-of-turtles radius
Arranges the given turtles in a circle centered on the patch at the center of the world with the given radius. (If the world has an even size the
center of the circle is rounded down to the nearest patch.) The turtles point outwards.
If the first input is an agentset, the turtles are arranged in random order.
If the first input is a list, the turtles are arranged clockwise in the given order, starting at the top of the circle. (Any non-turtles in the list are
ignored.)
;; in random order
layout-circle turtles 10
;; in order by who number
layout-circle sort turtles 10
;; in order by size
layout-circle sort-by [ [a b] -> [size] of a < [size] of b ] turtles 10
layout-radial
Since 4.0
layout-radial turtle-set link-set root-agent
Arranges the turtles in turtle-set connected by links in link-set, in a radial tree layout, centered around the root-agent which is moved to the
center of the world view.
Only links in the link-set will be used to determine the layout. If links connect turtles that are not in turtle-set those turtles will remain
stationary.
Even if the network does contain cycles, and is not a true tree structure, this layout will still work, although the results will not always be
pretty.
to make-a-tree
set-default-shape turtles "circle"
crt 6
ask turtle 0 [
create-link-with turtle 1
create-link-with turtle 2
create-link-with turtle 3
]
ask turtle 1 [
create-link-with turtle 4
create-link-with turtle 5
]
; do a radial tree layout, centered on turtle 0
layout-radial turtles links (turtle 0)
end
layout-spring
Since 4.0
layout-spring turtle-set link-set spring-constant spring-length repulsion-constant
Arranges the turtles in turtle-set, as if the links in link-set are springs and the turtles are repelling each other. Turtles that are connected by
links in link-set but not included in turtle-set are treated as anchors and are not moved.
spring-constant is a measure of the "tautness" of the spring. It is the "resistance" to change in their length. spring-constant is the force the
spring would exert if it's length were changed by 1 unit.
spring-length is the "zero-force" length or the natural length of the springs. This is the length which all springs try to achieve either by pushing
out their nodes or pulling them in.
repulsion-constant is a measure of repulsion between the nodes. It is the force that 2 nodes at a distance of 1 unit will exert on each other.
The repulsion effect tries to get the nodes as far as possible from each other, in order to avoid crowding and the spring effect tries to keep
them at "about" a certain distance from the nodes they are connected to. The result is the laying out of the whole network in a way which
highlights relationships among the nodes and at the same time is crowded less and is visually pleasing.
The layout algorithm is based on the Fruchterman-Reingold layout algorithm. More information about this algorithm can be obtained here.
to make-a-triangle
set-default-shape turtles
crt 3
ask turtle 0
[
create-links-with other
]
ask turtle 1
[
create-link-with turtle
]
repeat 30 [ layout-spring
end
"circle"
turtles
2
turtles links 0.2 5 1 ] ;; lays the nodes in a triangle
layout-tutte
Since 4.0
layout-tutte turtle-set link-set radius
The turtles that are connected by links in link-set but not included in turtle-set are placed in a circle layout with the given radius. There should
be at least 3 agents in this agentset.
The turtles in turtle-set are then laid out in the following manner: Each turtle is placed at centroid (or barycenter) of the polygon formed by its
linked neighbors. (The centroid is like a 2-dimensional average of the coordinates of the neighbors.)
(The purpose of the circle of "anchor agents" is to prevent all the turtles from collapsing down to one point.)
After a few iterations of this, the layout will stabilize.
This layout is named after the mathematician William Thomas Tutte, who proposed it as a method for graph layout.
to make-a-tree
set-default-shape turtles
crt 6
ask turtle 0 [
create-link-with turtle
create-link-with turtle
create-link-with turtle
]
"circle"
1
2
3
ask turtle 1 [
create-link-with turtle 4
create-link-with turtle 5
]
; place all the turtles with just one
; neighbor on the perimeter of a circle
; and then place the remaining turtles inside
; this circle, spread between their neighbors.
repeat 10 [ layout-tutte (turtles with [link-neighbors = 1]) links 12 ]
end
left
lt
Since 1.0
Since 1.0
left number
The turtle turns left by number degrees. (If number is negative, it turns right.)
length
Since 1.0
length list
length string
Reports the number of items in the given list, or the number of characters in the given string.
let
Since 2.1
let variable value
Creates a new local variable and gives it the given value. A local variable is one that exists only within the enclosing block of commands.
If you want to change the value afterwards, use set.
Example:
let prey one-of sheep-here
if prey != nobody
[ ask prey [ die ] ]
link
Since 4.0
link end1 end2
end1 end2
Given the who numbers of the endpoints, reports the link connecting the turtles. If there is no such link reports nobody. To refer to breeded
links you must use the singular breed form with the endpoints.
ask link 0 1 [ set color green ]
;; unbreeded link connecting turtle 0 and turtle 1 will turn green
ask directed-link 0 1 [ set color red ]
;; directed link connecting turtle 0 and turtle 1 will turn red
See also patch-at.
link-heading
Since 4.0
link-heading
Reports the heading in degrees (at least 0, less than 360) from end1 to end2 of the link. Throws a runtime error if the endpoints are at the
same location.
ask link 0 1 [ print link-heading ]
;; prints [[towards other-end] of end1] of link 0 1
See also link-length
link-length
link-length
Reports the distance between the endpoints of the link.
ask link 0 1 [ print link-length ]
;; prints [[distance other-end] of end1] of link 0 1
See also link-heading
Since 4.0
link-set
Since 4.0
link-set value
(link-set value1 value2 ...)
Reports an agentset containing all of the links anywhere in any of the inputs. The inputs may be individual links, link agentsets, nobody, or
lists (or nested lists) containing any of the above.
link-set self
link-set [my-links] of nodes with [color = red]
See also turtle-set, patch-set.
link-shapes
Since 4.0
link-shapes
Reports a list of strings containing all of the link shapes in the model.
New shapes can be created, or imported from other models, in the Link Shapes Editor.
show link-shapes
=> ["default"]
links
Since 4.0
links
Reports the agentset consisting of all links.
show count links
;; prints the number of links
links-own
links-own [var1 ...]
-own [var1 ...]
The links-own keyword, like the globals, breed, -own, turtles-own, and patches-own keywords, can only be used at the beginning of
a program, before any function definitions. It defines the variables belonging to each link.
If you specify a breed instead of "links", only links of that breed have the listed variables. (More than one link breed may list the same
variable.)
undirected-link-breed [sidewalks sidewalk]
directed-link-breed [streets street]
links-own [traffic]
;; applies to all breeds
sidewalks-own [pedestrians]
streets-own [cars bikes]
list
Since 1.0
list value1 value2
(list value1 ...)
Reports a list containing the given items. The items can be of any type, produced by any kind of reporter.
show list (random 10) (random 10)
=> [4 9] ;; or similar list
show (list 5)
=> [5]
show (list (random 10) 1 2 3 (random 10))
=> [4 1 2 3 9] ;; or similar list
ln
Since 1.0
ln number
Reports the natural logarithm of number, that is, the logarithm to the base e (2.71828...).
See also e, log.
log
log number base
Reports the logarithm of number in base base.
Since 1.0
show log 64 2
=> 6
See also ln.
loop
Since 1.0
loop [ commands ]
Repeats the commands forever, or until the enclosing procedure exits through use of the stop or report commands.
to move-to-world-edge ;; turtle procedure
loop [
if not can-move? 1 [ stop ]
fd 1
]
end
In this example, stop exits not just the loop, but the entire procedure.
Note: in many circumstances, it is more appropriate to use a forever button to repeat something indefinitely. See Buttons in the Programming
Guide.
lput
Since 1.0
lput value list
Adds value to the end of a list and reports the new list.
;; suppose mylist is [2 7 10 "Bob"]
set mylist lput 42 mylist
;; mylist now is [2 7 10 "Bob" 42]
M
map
Since 1.3
map reporter list
(map reporter list1 ...)
With a single list, the given reporter is run for each item in the list, and a list of the results is collected and reported. reporter may be an
anonymous reporter or the name of a reporter.
show map round [1.1 2.2 2.7]
=> [1 2 3]
show map [ i -> i * i ] [1 2 3]
=> [1 4 9]
With multiple lists, the given reporter is run for each group of items from each list. So, it is run once for the first items, once for the second
items, and so on. All the lists must be the same length.
Some examples make this clearer:
show (map + [1 2 3] [2 4 6])
=> [3 6 9]
show (map [ [a b c] -> a + b = c ] [1 2 3] [2 4 6] [3 5 9])
=> [true false true]
See also foreach, -> (anonymous procedure).
max
Since 1.0
max list
Reports the maximum number value in the list. It ignores other types of items.
show max [xcor] of turtles
;; prints the x coordinate of the turtle which is
;; farthest right in the world
show max list a b
;; prints the larger of the two variables a and b
show max (list a b c)
;; prints the largest of the three variables a, b, and c
max-n-of
Since 4.0
max-n-of number agentset [reporter]
Reports an agentset containing number agents from agentset with the highest values of reporter. The agentset is built by finding all the
agents with the highest value of reporter, if there are not number agents with that value then agents with the second highest value are found,
and so on. At the end, if there is a tie that would make the resulting agentset too large, the tie is broken randomly.
;; assume the world is 11 x 11
show max-n-of 5 patches [pxcor]
;; shows 5 patches with pxcor = max-pxcor
show max-n-of 5 patches with [pycor = 0] [pxcor]
;; shows an agentset containing:
;; (patch 1 0) (patch 2 0) (patch 3 0) (patch 4 0) (patch 5 0)
See also max-one-of, with-max.
max-one-of
Since 1.0
max-one-of agentset [reporter]
Reports the agent in the agentset that has the highest value for the given reporter. If there is a tie this command reports one random agent
with the highest value. If you want all such agents, use with-max instead.
show max-one-of patches [count turtles-here]
;; prints the first patch with the most turtles on it
See also max-n-of, with-max.
max-pxcor
max-pycor
Since 3.1
Since 3.1
max-pxcor
max-pycor
These reporters give the maximum x-coordinate and maximum y-coordinate, (respectively) for patches, which determines the size of the
world.
Unlike in older versions of NetLogo the origin does not have to be at the center of the world. However, the maximum x- and y- coordinates
must be greater than or equal to zero.
Note: You can set the size of the world only by editing the view -- these are reporters which cannot be set.
crt 100 [ setxy random-float max-pxcor
random-float max-pycor ]
;; distributes 100 turtles randomly in the
;; first quadrant
See also min-pxcor, min-pycor, world-width, and world-height
mean
Since 1.0
mean list
Reports the statistical mean of the numeric items in the given list. Errors on non-numeric items. The mean is the average, i.e., the sum of the
items divided by the total number of items.
show mean [xcor] of turtles
;; prints the average of all the turtles' x coordinates
median
Since 1.0
median list
Reports the statistical median of the numeric items of the given list. Ignores non-numeric items. The median is the item that would be in the
middle if all the items were arranged in order. (If two items would be in the middle, the median is the average of the two.)
show median [xcor] of turtles
;; prints the median of all the turtles' x coordinates
member?
member? value list
member? string1 string2
member? agent agentset
For a list, reports true if the given value appears in the given list, otherwise reports false.
For a string, reports true or false depending on whether string1 appears anywhere inside string2 as a substring.
For an agentset, reports true if the given agent is appears in the given agentset, otherwise reports false.
show member? 2 [1 2 3]
=> true
show member? 4 [1 2 3]
=> false
show member? "bat" "abate"
=> true
Since 1.0
show member? turtle 0 turtles
=> true
show member? turtle 0 patches
=> false
See also position.
min
Since 1.0
min list
Reports the minimum number value in the list. It ignores other types of items.
show min [xcor] of turtles
;; prints the lowest x-coordinate of all the turtles
show min list a b
;; prints the smaller of the two variables a and b
show min (list a b c)
;; prints the smallest of the three variables a, b, and c
min-n-of
Since 4.0
min-n-of number agentset [reporter]
Reports an agentset containing number agents from agentset with the lowest values ofreporter. The agentset is built by finding all the agents
with the lowest value of reporter, if there are not number agents with that value then the agents with the second lowest value are found, and
so on. At the end, if there is a tie that would make the resulting agentset too large, the tie is broken randomly.
;; assume the world is 11 x 11
show min-n-of 5 patches [pxcor]
;; shows 5 patches with pxcor = min-pxcor
show min-n-of 5 patches with [pycor = 0] [pxcor]
;; shows an agentset containing:
;; (patch -5 0) (patch -4 0) (patch -3 0) (patch -2 0) (patch -1 0)
See also min-one-of, with-min.
min-one-of
Since 1.0
min-one-of agentset [reporter]
Reports a random agent in the agentset that reports the lowest value for the given reporter. If there is a tie, this command reports one
random agent that meets the condition. If you want all such agents use with-min instead.
show min-one-of turtles [xcor + ycor]
;; reports the first turtle with the smallest sum of
;; coordinates
See also with-min, min-n-of.
min-pxcor
min-pycor
Since 3.1
Since 3.1
min-pxcor
min-pycor
These reporters give the minimum x-coordinate and minimum y-coordinate, (respectively) for patches, which determines the size of the world.
Unlike in older versions of NetLogo the origin does not have to be at the center of the world. However, the minimum x- and y- coordinates
must be less than or equal to zero.
Note: You can set the size of the world only by editing the view -- these are reporters which cannot be set.
crt 100 [ setxy random-float min-pxcor
random-float min-pycor ]
;; distributes 100 turtles randomly in the
;; third quadrant
See also max-pxcor, max-pycor, world-width, and world-height
mod
Since 1.0
number1 mod number2
Reports number1 modulo number2: that is, the residue of number1 (mod number2). mod is is equivalent to the following NetLogo code:
number1 - (floor (number1 / number2)) * number2
Note that mod is "infix", that is, it comes between its two inputs.
show 62 mod 5
=> 2
show -8 mod 3
=> 1
See also remainder. mod and remainder behave the same for positive numbers, but differently for negative numbers.
modes
Since 2.0
modes list
Reports a list of the most common item or items in list.
The input list may contain any NetLogo values.
If the input is an empty list, reports an empty list.
show modes [1 2 2 3 4]
=> [2]
show modes [1 2 2 3 3 4]
=> [2 3]
show modes [ [1 2 [3]] [1 2 [3]] [2 3 4] ]
=> [[1 2 [3]]]
show modes [pxcor] of turtles
;; shows which columns of patches have the most
;; turtles on them
mouse-down?
Since 1.0
mouse-down?
Reports true if the mouse button is down, false otherwise.
Note: If the mouse pointer is outside of the current view , mouse-down? will always report false.
mouse-inside?
Since 3.0
mouse-inside?
Reports true if the mouse pointer is inside the current view, false otherwise.
mouse-xcor
mouse-ycor
Since 1.0
Since 1.0
mouse-xcor
mouse-ycor
Reports the x or y coordinate of the mouse in the 2D view. The value is in terms of turtle coordinates, so it might not be an integer. If you want
patch coordinates, use round mouse-xcor and round mouse-ycor.
Note: If the mouse is outside of the 2D view, reports the value from the last time it was inside.
;; to make the mouse "draw" in red:
if mouse-down?
[ ask patch mouse-xcor mouse-ycor [ set pcolor red ] ]
move-to
Since 4.0
move-to agent
The turtle sets its x and y coordinates to be the same as the given agent's.
(If that agent is a patch, the effect is to move the turtle to the center of that patch.)
move-to turtle 5
;; turtle moves to same point as turtle 5
move-to one-of patches
;; turtle moves to the center of a random patch
move-to max-one-of turtles [size]
;; turtle moves to same point as biggest turtle
Note that the turtle's heading is unaltered. You may want to use the face command first to orient the turtle in the direction of motion.
See also setxy.
my-
my-links
my-
my-links
Since 4.0
Reports an agentset of all links connected to the caller of the corresponding breed, regardless of directedness. Generally, you might consider
using my-out-links instead of this primitive, as it works well for either directed or undirected networks (since it excludes directed, incoming
links).
crt 5
ask turtle 0
[
create-links-with other turtles
show my-links ;; prints the agentset containing all links
;; (since all the links we created were with turtle 0 )
]
ask turtle 1
[
show my-links ;; shows an agentset containing the link 0 1
]
end
If you only want the undirected links connected to a node, you can do my-links with [ not is-directed-link? self ].
my-in-
my-in-links
Since 4.0
my-in-
my-in-links
Reports an agentset of all the directed links coming in from other nodes to the caller as well as all undirected links connected to the caller.
You can think of this as "all links that you can use to travel to this node".
crt 5
ask turtle 0
[
create-links-to other turtles
show my-in-links ;; shows an empty agentset
]
ask turtle 1
[
show my-in-links ;; shows an agentset containing the link 0 1
]
my-out-
my-out-links
Since 4.0
my-out-
my-out-links
Reports an agentset of all the directed links going out from the caller to other nodes as well as undirected links connected to the caller. You
can think of this as "all links you can use to travel from this node".
crt 5
ask turtle 0
[
create-links-to other turtles
show my-out-links ;; shows agentset containing all the links
]
ask turtle 1
[
show my-out-links ;; shows an empty agentset
]
myself
Since 1.0
myself
"self" and "myself" are very different. "self" is simple; it means "me". "myself" means "the turtle, patch or link who asked me to do what I'm
doing right now."
When an agent has been asked to run some code, using myself in that code reports the agent (turtle, patch or link) that did the asking.
myself is most often used in conjunction with of to read or set variables in the asking agent.
myself can be used within blocks of code not just in the ask command, but also hatch, sprout, of, with, all?, with-min, with-max, min-one-of,
max-one-of, min-n-of, max-n-of.
ask turtles
[ ask patches in-radius 3
[ set pcolor [color] of myself ] ]
;; each turtle makes a colored "splotch" around itself
See the "Myself Example" code example for more examples.
See also self.
N
n-of
Since 3.1
n-of size agentset
n-of size list
From an agentset, reports an agentset of size size randomly chosen from the input set, with no repeats.
From a list, reports a list of size size randomly chosen from the input set, with no repeats. The items in the result appear in the same order
that they appeared in the input list. (If you want them in random order, use shuffle on the result.)
It is an error for size to be greater than the size of the input.
ask n-of 50 patches [ set pcolor green ]
;; 50 randomly chosen patches turn green
See also one-of.
n-values
Since 2.0
n-values size reporter
Reports a list of length size containing values computed by repeatedly running the reporter. reporter may be an anonymous reporter or the
name of a reporter.
If the reporter accepts inputs, the input will be the number of the item currently being computed, starting from zero.
show n-values 5 [1]
=> [1 1 1 1 1]
show n-values 5 [ i -> i ]
=> [0 1 2 3 4]
show n-values 3 turtle
=> [(turtle 0) (turtle 1) (turtle 2)]
show n-values 5 [ x -> x * x ]
=> [0 1 4 9 16]
See also reduce, filter, -> (anonymous procedure), range.
neighbors
neighbors4
Since 1.1
Since 1.1
neighbors
neighbors4
Reports an agentset containing the 8 surrounding patches (neighbors) or 4 surrounding patches (neighbors4).
show sum [count turtles-here] of neighbors
;; prints the total number of turtles on the eight
;; patches around this turtle or patch
show count turtles-on neighbors
;; a shorter way to say the same thing
ask neighbors4 [ set pcolor red ]
;; turns the four neighboring patches red
-neighbors
link-neighbors
Since 4.0
-neighbors
link-neighbors
Reports the agentset of all turtles found at the other end of any links (undirected or directed, incoming or outgoing) connected to this turtle.
crt 3
ask turtle 0
[
create-links-with other turtles
ask link-neighbors [ set color red ] ;; turtles 1 and 2 turn red
]
ask turtle 1
[
ask link-neighbors [ set color blue ] ;; turtle 0 turns blue
]
end
-neighbor?
link-neighbor?
-neighbor? turtle
link-neighbor? turtle
Reports true if there is a link (either directed or undirected, incoming or outgoing) between turtle and the caller.
Since 4.0
crt 2
ask turtle 0
[
create-link-with turtle 1
show link-neighbor? turtle 1
]
ask turtle 1
[
show link-neighbor? turtle 0
]
;; prints true
;; prints true
netlogo-version
Since 3.0
netlogo-version
Reports a string containing the version number of the NetLogo you are running.
show netlogo-version
=> "6.0.1"
netlogo-web?
Since 5.2
netlogo-web?
Reports true if the model is running in NetLogo Web.
new-seed
Since 3.0
new-seed
Reports a number suitable for seeding the random number generator.
The numbers reported by new-seed are based on the current date and time in milliseconds and lie in the generator's usable range of seeds, 2147483648 to 2147483647.
new-seed never reports the same number twice in succession, even across parallel BehaviorSpace runs. (This is accomplished by waiting a
millisecond if the seed for the current millisecond was already used.)
See also random-seed.
no-display
Since 1.0
no-display
Turns off all updates to the current view until the display command is issued. This has two major uses.
One, you can control when the user sees view updates. You might want to change lots of things on the view behind the user's back, so to
speak, then make them visible to the user all at once.
Two, your model will run faster when view updating is off, so if you're in a hurry, this command will let you get results faster. (Note that
normally you don't need to use no-display for this, since you can also use the on/off switch in view control strip to freeze the view.)
Note that display and no-display operate independently of the switch in the view control strip that freezes the view.
See also display.
nobody
nobody
This is a special value which some primitives such as turtle, one-of, max-one-of, etc. report to indicate that no agent was found. Also, when a
turtle dies, it becomes equal to nobody.
Note: Empty agentsets are not equal to nobody. If you want to test for an empty agentset, use any?. You only get nobody back in situations
where you were expecting a single agent, not a whole agentset.
set target one-of other turtles-here
if target != nobody
[ ask target [ set color red ] ]
no-links
Since 4.0
no-links
Reports an empty link agentset.
no-patches
no-patches
Since 4.0
Reports an empty patch agentset.
not
Since 1.0
not boolean
Reports true if boolean is false, otherwise reports false.
if not any? turtles [ crt 10 ]
no-turtles
Since 4.0
no-turtles
Reports an empty turtle agentset.
O
of
Since 4.0
[reporter] of agent
[reporter] of agentset
For an agent, reports the value of the reporter for that agent (turtle or patch).
show [pxcor] of patch 3 5
;; prints 3
show [pxcor] of one-of patches
;; prints the value of a random patch's pxcor variable
show [who * who] of turtle 5
=> 25
show [count turtles in-radius 3] of patch 0 0
;; prints the number of turtles located within a
;; three-patch radius of the origin
For an agentset, reports a list that contains the value of the reporter for each agent in the agentset (in random order).
crt 4
show sort
=> [0 1 2
show sort
=> [0 1 4
[who] of turtles
3]
[who * who] of turtles
9]
one-of
Since 1.0
one-of agentset
one-of list
From an agentset, reports a random agent. If the agentset is empty, reports nobody.
From a list, reports a random list item. It is an error for the list to be empty.
ask one-of patches [ set pcolor green ]
;; a random patch turns green
ask patches with [any? turtles-here]
[ show one-of turtles-here ]
;; for each patch containing turtles, prints one of
;; those turtles
;; suppose mylist is [1 2 3 4 5 6]
show one-of mylist
;; prints a value randomly chosen from the list
See also n-of.
or
Since 1.0
boolean1 or boolean2
Reports true if either boolean1 or boolean2, or both, is true.
Note that if condition1 is true, then condition2 will not be run (since it can't affect the result).
if (pxcor > 0) or (pycor > 0) [ set pcolor red ]
;; patches turn red except in lower-left quadrant
other
other agentset
Since 4.0
Reports an agentset which is the same as the input agentset but omits this agent.
show count turtles-here
=> 10
show count other turtles-here
=> 9
other-end
Since 4.0
other-end
If run by a turtle, reports the turtle at the other end of the asking link.
If run by a link, reports the turtle at the end of the link that isn't the asking turtle.
These definitions are difficult to understand in the abstract, but the following examples should help:
ask
ask
ask
ask
turtle
turtle
turtle
link 0
0
0
1
1
[
[
[
[
create-link-with turtle 1 ]
ask link 0 1 [ show other-end ] ] ;; prints turtle 1
ask link 0 1 [ show other-end ] ] ;; prints turtle 0
ask turtle 0 [ show other-end ] ] ;; prints turtle 1
As these examples hopefully make plain, the "other" end is the end that is neither asking nor being asked.
out--neighbor?
out-link-neighbor?
Since 4.0
out--neighbor? turtle
out-link-neighbor? turtle
Reports true if there is a directed link going from the caller to turtle or if there is an undirected link connecting the caller with turtle. You can
think of this as "can I get from the caller to turtle using a link?"
crt 2
ask turtle 0 [
create-link-to turtle 1
show in-link-neighbor? turtle 1
show out-link-neighbor? turtle 1
]
ask turtle 1 [
show in-link-neighbor? turtle 0
show out-link-neighbor? turtle 0
]
;; prints false
;; prints true
;; prints true
;; prints false
out--neighbors
out-link-neighbors
Since 4.0
out--neighbors
out-link-neighbors
Reports the agentset of all the turtles that have directed links from the caller, or undirected links with the caller. You can think of this as "who
can I get to from the caller using a link?"
crt 4
ask turtle 0
[
create-links-to other turtles
ask out-link-neighbors [ set color pink ] ;; turtles 1-3 turn pink
]
ask turtle 1
[
ask out-link-neighbors [ set color orange ] ;; no turtles change colors
;; since turtle 1 only has in-links
]
end
out--to
out-link-to
Since 4.0
out--to turtle
out-link-to turtle
Reports a directed link from the caller to turtle or an undirected link connecting the two. If no link exists then it reports nobody. If more than
one such link exists, reports a random one. You can think of this as "give me a link that I can use to travel from the caller to turtle."
crt 2
ask turtle 0 [
create-link-to turtle 1
show out-link-to turtle 1 ;; shows link 0 1
]
ask turtle 1
[
]
show out-link-to turtle 0 ;; shows nobody
See also: in-link-from link-with
output-print
output-show
output-type
output-write
Since 2.1
Since 2.1
Since 2.1
Since 2.1
output-print value
output-show value
output-type value
output-write value
These commands are the same as the print, show, type, and write commands except that value is printed in the model's output area, instead
of in the Command Center. (If the model does not have a separate output area, then the Command Center is used.)
P
patch
Since 1.0
patch xcor ycor
Given the x and y coordinates of a point, reports the patch containing that point. (The coordinates are absolute coordinates; they are not
computed relative to this agent, as with patch-at.)
If x and y are integers, the point is the center of a patch. If x or y is not an integer, rounding to the nearest integer is used to determine which
patch contains the point.
If wrapping is allowed by the topology, the given coordinates will be wrapped to be within the world. If wrapping is not allowed and the given
coordinates are outside the world, reports nobody.
ask patch 3 -4 [ set pcolor green ]
;; patch with pxcor of 3 and pycor of -4 turns green
show patch 1.2 3.7
;; prints (patch 1 4); note rounding
show patch 18 19
;; supposing min-pxcor and min-pycor are -17
;; and max-pxcor and max-pycor are 17,
;; in a wrapping topology, prints (patch -17 -16);
;; in a non-wrapping topology, prints nobody
See also patch-at.
patch-ahead
Since 2.0
patch-ahead distance
Reports the single patch that is the given distance "ahead" of this turtle, that is, along the turtle's current heading. Reports nobody if the patch
does not exist because it is outside the world.
ask patch-ahead 1 [ set pcolor green ]
;; turns the patch 1 in front of this turtle
;;
green; note that this might be the same patch
;;
the turtle is standing on
See also patch-at, patch-left-and-ahead, patch-right-and-ahead, patch-at-heading-and-distance.
patch-at
Since 1.0
patch-at dx dy
Reports the patch at (dx, dy) from the caller, that is, the patch containing the point dx east and dy patches north of this agent.
Reports nobody if there is no such patch because that point is beyond a non-wrapping world boundary.
ask patch-at 1 -1 [ set pcolor green ]
;; if caller is a turtle or patch, turns the
;;
patch just southeast of the caller green
See also patch, patch-ahead, patch-left-and-ahead, patch-right-and-ahead, patch-at-heading-and-distance.
patch-at-heading-and-distance
patch-at-heading-and-distance heading distance
Since 2.0
patch-at-heading-and-distance reports the single patch that is the given distance from this turtle or patch, along the given absolute heading.
(In contrast to patch-left-and-ahead and patch-right-and-ahead, this turtle's current heading is not taken into account.) Reports nobody if the
patch does not exist because it is outside the world.
ask patch-at-heading-and-distance -90 1 [ set pcolor green ]
;; turns the patch 1 to the west of this patch green
See also patch, patch-at, patch-left-and-ahead, patch-right-and-ahead.
patch-here
Since 1.0
patch-here
patch-here reports the patch under the turtle.
Note that this reporter isn't available to a patch because a patch can just say "self".
patch-left-and-ahead
patch-right-and-ahead
Since 2.0
Since 2.0
patch-left-and-ahead angle distance
patch-right-and-ahead angle distance
Reports the single patch that is the given distance from this turtle, in the direction turned left or right the given angle (in degrees) from the
turtle's current heading. Reports nobody if the patch does not exist because it is outside the world.
(If you want to find a patch in a given absolute heading, rather than one relative to the current turtle's heading, use patch-at-heading-anddistance instead.)
ask patch-right-and-ahead 30 1 [ set pcolor green ]
;; this turtle "looks" 30 degrees right of its
;;
current heading at the patch 1 unit away, and turns
;;
that patch green; note that this might be the same
;;
patch the turtle is standing on
See also patch, patch-at, patch-at-heading-and-distance.
patch-set
Since 4.0
patch-set value1
(patch-set value1 value2 ...)
Reports an agentset containing all of the patches anywhere in any of the inputs. The inputs may be individual patches, patch agentsets,
nobody, or lists (or nested lists) containing any of the above.
patch-set self
patch-set patch-here
(patch-set self neighbors)
(patch-set patch-here neighbors)
(patch-set patch 0 0 patch 1 3 patch 4 -2)
(patch-set patch-at -1 1 patch-at 0 1 patch-at 1 1)
patch-set [patch-here] of turtles
patch-set [neighbors] of turtles
See also turtle-set, link-set.
patch-size
Since 4.1
patch-size
Reports the size of the patches in the view in pixels. The size is typically an integer, but may also be a floating point number.
See also set-patch-size.
patches
Since 1.0
patches
Reports the agentset consisting of all patches.
patches-own
patches-own [var1 ...]
This keyword, like the globals, breed, -own, and turtles-own keywords, can only be used at the beginning of a program, before any
function definitions. It defines the variables that all patches can use.
All patches will then have the given variables and be able to use them.
All patch variables can also be directly accessed by any turtle standing on the patch.
See also globals, turtles-own, breed, -own.
pcolor
pcolor
This is a built-in patch variable. It holds the color of the patch. You can set this variable to make the patch change color.
All patch variables can be directly accessed by any turtle standing on the patch. Color can be represented either as a NetLogo color (a single
number) or an RGB color (a list of 3 numbers). See details in the Colors section of the Programming Guide.
See also color.
pen-down
pd
pen-erase
pe
pen-up
pu
Since 1.0
Since 1.0
Since 3.0
Since 3.0
Since 1.0
Since 1.0
pen-down
pen-erase
pen-up
The turtle changes modes between drawing lines, removing lines or neither. The lines will always be displayed on top of the patches and
below the turtles. To change the color of the pen set the color of the turtle using set color.
Note: When a turtle's pen is down, all movement commands cause lines to be drawn, including jump, setxy, and move-to.
Note: These commands are equivalent to setting the turtle variable "pen-mode" to "down" , "up", and "erase".
Note: On Windows drawing and erasing a line might not erase every pixel.
pen-mode
This is a built-in turtle variable. It holds the state of the turtle's pen. You set the variable to draw lines, erase lines or stop either of these
actions. Possible values are "up", "down", and "erase".
pen-size
This is a built-in turtle variable. It holds the width of the line, in pixels, that the turtle will draw (or erase) when the pen is down (or erasing).
plabel
plabel
This is a built-in patch variable. It may hold a value of any type. The patch appears in the view with the given value "attached" to it as text.
You can set this variable to add, change, or remove a patch's label.
All patch variables can be directly accessed by any turtle standing on the patch.
See also plabel-color, label, label-color.
plabel-color
plabel-color
This is a built-in patch variable. It holds a number greater than or equal to 0 and less than 140. This number determines what color the
patch's label appears in (if it has a label). You can set this variable to change the color of a patch's label.
All patch variables can be directly accessed by any turtle standing on the patch.
See also plabel, label, label-color.
plot
plot number
Since 1.0
Increments the x-value of the plot pen by plot-pen-interval, then plots a point at the updated x-value and a y-value of number. (The first time
the command is used on a plot, the point plotted has an x-value of 0.)
plot-name
Since 1.0
plot-name
Reports the name of the current plot (a string)
plot-pen-exists?
Since 4.0
plot-pen-exists? string
Reports true if a plot pen with the given name is defined in the current plot. Otherwise reports false.
plot-pen-down
plot-pen-up
Since 1.0
Since 1.0
plot-pen-down
plot-pen-up
Puts down (or up) the current plot-pen, so that it draws (or doesn't). (By default, all pens are down initially.)
plot-pen-reset
Since 1.0
plot-pen-reset
Clears everything the current plot pen has drawn, moves it to (0,0), and puts it down. If the pen is a permanent pen, the color, mode, and
interval are reset to the default values from the plot Edit dialog.
plotxy
Since 1.0
plotxy number1 number2
Moves the current plot pen to the point with coordinates (number1, number2). If the pen is down, a line, bar, or point will be drawn (depending
on the pen's mode).
plot-x-min
plot-x-max
plot-y-min
plot-y-max
Since 1.0
Since 1.0
Since 1.0
Since 1.0
plot-x-min
plot-x-max
plot-y-min
plot-y-max
Reports the minimum or maximum value on the x or y axis of the current plot.
These values can be set with the commands set-plot-x-range and set-plot-y-range. (Their default values are set from the plot Edit dialog.)
position
Since 1.0
position item list
position string1 string2
On a list, reports the first position of item in list, or false if it does not appear.
On strings, reports the position of the first appearance string1 as a substring of string2, or false if it does not appear.
Note: The positions are numbered beginning with 0, not with 1.
;; suppose mylist is [2 7 4 7 "Bob"]
show position 7 mylist
=> 1
show position 10 mylist
=> false
show position "in" "string"
=> 3
See also member?.
precision
precision number places
Reports number rounded to places decimal places.
Since 1.0
If places is negative, the rounding takes place to the left of the decimal point.
show precision 1.23456789 3
=> 1.235
show precision 3834 -3
=> 4000
See also round, ceiling, floor.
print
Since 1.0
print value
Prints value in the Command Center, followed by a carriage return.
This agent is not printed before the value, unlike show.
See also show, type, and write.
See also output-print.
pxcor
pycor
pxcor
pycor
These are built-in patch variables. They hold the x and y coordinate of the patch. They are always integers. You cannot set these variables,
because patches don't move.
pxcor is greater than or equal to min-pxcor and less than or equal to max-pxcor; similarly for pycor and min-pycor and max-pycor.
All patch variables can be directly accessed by any turtle standing on the patch.
See also xcor, ycor.
R
random
Since 1.0
random number
If number is positive, reports a random integer greater than or equal to 0, but strictly less than number.
If number is negative, reports a random integer less than or equal to 0, but strictly greater than number.
If number is zero, the result is always 0 as well.
Note: In versions of NetLogo prior to version 2.0, this primitive reported a floating point number if given a non-integer input. This is no longer
the case. If you want a floating point answer, you must now use random-float instead.
show random 3
;; prints 0, 1, or 2
show random -3
;; prints 0, -1, or -2
show random 3.5
;; prints 0, 1, 2, or 3
See also random-float.
random-float
Since 2.0
random-float number
If number is positive, reports a random floating point number greater than or equal to 0 but strictly less than number.
If number is negative, reports a random floating point number less than or equal to 0, but strictly greater than number.
If number is zero, the result is always 0.
show random-float 3
;; prints a number at least 0 but less than 3,
;; for example 2.589444906014774
show random-float 2.5
;; prints a number at least 0 but less than 2.5,
;; for example 1.0897423196760796
random-exponential
random-gamma
random-normal
random-poisson
Since 1.2.1
Since 2.0
Since 1.2.1
Since 1.2.1
random-exponential mean
random-gamma alpha lambda
random-normal mean standard-deviation
random-poisson mean
Reports an accordingly distributed random number with the mean and, in the case of the normal distribution, the standard-deviation. (The
standard deviation may not be negative.)
random-exponential reports an exponentially distributed random floating point number. It is equivalent to (- mean) * ln random-float 1.0.
random-gamma reports a gamma-distributed random floating point number as controlled by the floating point alpha and lambda parameters.
Both inputs must be greater than zero. (Note: for results with a given mean and variance, use inputs as follows: alpha = mean * mean /
variance; lambda = 1 / (variance / mean).)
random-normal reports a normally distributed random floating point number.
random-poisson reports a Poisson-distributed random integer.
show random-exponential 2
;; prints an exponentially distributed random floating
;; point number with a mean of 2
show random-normal 10.1 5.2
;; prints a normally distributed random floating point
;; number with a mean of 10.1 and a standard deviation
;; of 5.2
show random-poisson 3.4
;; prints a Poisson-distributed random integer with a
;; mean of 3.4
random-pxcor
random-pycor
Since 3.1
Since 3.1
random-pxcor
random-pycor
Reports a random integer ranging from min-pxcor (or -y) to max-pxcor (or -y) inclusive.
ask turtles [
;; move each turtle to the center of a random patch
setxy random-pxcor random-pycor
]
See also random-xcor, random-ycor.
random-seed
Since 1.0
random-seed number
Sets the seed of the pseudo-random number generator to the integer part of number. The seed must be in the range -2147483648 to
2147483647; note that this is smaller than the full range of integers supported by NetLogo (-9007199254740992 to 9007199254740992).
See the Random Numbers section of the Programming Guide for more details.
random-seed
show random
=> 50
show random
=> 35
random-seed
show random
=> 50
show random
=> 35
47822
100
100
47822
100
100
random-xcor
random-ycor
Since 3.1
Since 3.1
random-xcor
random-ycor
Reports a random floating point number from the allowable range of turtle coordinates along the given axis, x or y.
Turtle coordinates range from min-pxcor - 0.5 (inclusive) to max-pxcor + 0.5 (exclusive) horizontally; vertically, substitute -y for -x.
ask turtles [
;; move each turtle to a random point
setxy random-xcor random-ycor
]
See also random-pxcor, random-pycor.
range
range stop
(range start stop)
Since 6.0
(range start stop step)
Generates a list of numbers, starting at start, ending before stop, counting by step. start defaults to 0 and step defaults to 1.
show range 5
=> [0 1 2 3 4]
show (range 2 5)
=> [2 3 4]
show (range 2 5 0.5)
=> [2 2.5 3 3.5 4 4.5]
show (range 10 0 -1)
=> [10 9 8 7 6 5 4 3 2 1]
See also n-values
read-from-string
Since 1.1
read-from-string string
Interprets the given string as if it had been typed in the Command Center, and reports the resulting value. The result may be a number, list,
string, or boolean value, or the special value "nobody".
Useful in conjunction with the user-input primitive for converting the user's input into usable form.
show read-from-string "3" + read-from-string "5"
=> 8
show length read-from-string "[1 2 3]"
=> 3
crt read-from-string user-input "Make how many turtles?"
;; the number of turtles input by the user
;; are created
reduce
Since 1.3
reduce reporter list
Reduces a list from left to right using the given reporter, resulting in a single value. This means, for example, that reduce [ [a b] -> a + b]
[1 2 3 4] is equivalent to (((1 + 2) + 3) + 4). If list has a single item, that item is reported. It is an error to reduce an empty list. reporter may
be an anonymous reporter or the name of a reporter.
The first input passed to the reporter is the result so far, and the second input is the next item in the list.
Since it can be difficult to develop an intuition about what reduce does, here are some simple examples which, while not useful in themselves,
may give you a better understanding of this primitive:
show reduce + [1 2 3]
=> 6
show reduce - [1 2 3]
=> -4
show reduce [ [result-so-far next-item] -> next-item - result-so-far ] [1 2 3]
=> 2
show reduce [ [result-so-far ignored-item] -> result-so-far ] [1 2 3]
=> 1
show reduce [ [ignored next-item] -> next-item ] [1 2 3]
=> 3
show reduce sentence [[1 2] [3 [4]] 5]
=> [1 2 3 [4] 5]
show reduce [ [result-so-far next-item] -> fput next-item result-so-far ] (fput [] [1 2 3 4 5])
=> [5 4 3 2 1]
Here are some more useful examples:
;; find the longest string in a list
to-report longest-string [strings]
report reduce
[ [longest-so-far next-string] -> ifelse-value (length longest-so-far >= length next-string) [longest-so-far] [next-string] ]
strings
end
show longest-string ["hi" "there" "!"]
=> "there"
;; count the number of occurrences of an item in a list
to-report occurrences [x the-list]
report reduce
[ [occurrence-count next-item] -> ifelse-value (next-item = x) [occurrence-count + 1] [occurrence-count] ] (fput 0 the-list)
end
show occurrences 1 [1 2 1 3 1 2 3 1 1 4 5 1]
=> 6
;; evaluate the polynomial, with given coefficients, at x
to-report evaluate-polynomial [coefficients x]
report reduce [ [value coefficient] -> (x * value) + coefficient ] coefficients
end
;; evaluate 3x^2 + 2x + 1 at x = 4
show evaluate-polynomial [3 2 1] 4
=> 57
See also filter, -> (anonymous procedure.
remainder
Since 1.2.1
remainder number1 number2
Reports the remainder when number1 is divided by number2. This is equivalent to the following NetLogo code:
number1 - (int (number1 / number2)) * number2
show remainder 62 5
=> 2
show remainder -8 3
=> -2
See also mod. mod and remainder behave the same for positive numbers, but differently for negative numbers.
remove
Since 1.0
remove item list
remove string1 string2
For a list, reports a copy of list with all instances of item removed.
For strings, reports a copy of string2 with all the appearances of string1 as a substring removed.
set mylist [2 7 4 7 "Bob"]
set mylist remove 7 mylist
;; mylist is now [2 4 "Bob"]
show remove "to" "phototonic"
=> "phonic"
remove-duplicates
Since 1.0
remove-duplicates list
Reports a copy of list with all duplicate items removed. The first of each item remains in place.
set mylist [2 7 4 7 "Bob" 7]
set mylist remove-duplicates mylist
;; mylist is now [2 7 4 "Bob"]
remove-item
Since 2.0
remove-item index list
remove-item index string
For a list, reports a copy of list with the item at the given index removed.
For strings, reports a copy of string with the character at the given index removed.
Note that the indices begin from 0, not 1. (The first item is item 0, the second item is item 1, and so on.)
set mylist [2 7 4 7 "Bob"]
set mylist remove-item 2 mylist
;; mylist is now [2 7 7 "Bob"]
show remove-item 2 "string"
=> "sting"
repeat
Since 1.0
repeat number [ commands ]
Runs commands number times.
pd repeat 36 [ fd 1 rt 10 ]
;; the turtle draws a circle
replace-item
Since 1.0
replace-item index list value
replace-item index string1 string2
On a list, replaces an item in that list. index is the index of the item to be replaced, starting with 0. (The 6th item in a list would have an index
of 5.) Note that "replace-item" is used in conjunction with "set" to change a list.
Likewise for a string, but the given character of string1 removed and the contents of string2 spliced in instead.
show replace-item 2 [2 7 4 5] 15
=> [2 7 15 5]
show replace-item 1 "cat" "are"
=> "caret"
report
Since 1.0
report value
Immediately exits from the current to-report procedure and reports value as the result of that procedure. report and to-report are always used
in conjunction with each other. See to-report for a discussion of how to use them.
reset-perspective
rp
Since 3.0
Since 3.0
reset-perspective
The observer stops watching, following, or riding any turtles (or patches). (If it wasn't watching, following, or riding anybody, nothing
happens.) In the 3D view, the observer also returns to its default position (above the origin, looking straight down).
See also follow, ride, watch.
reset-ticks
Since 4.0
reset-ticks
Resets the tick counter to zero, sets up all plots, then updates all plots (so that the initial state of the world is plotted).
Normally reset-ticks goes at the end of a setup procedure.
See also clear-ticks, tick, ticks, tick-advance, setup-plots, update-plots.
reset-timer
Since 1.0
reset-timer
Resets the timer to zero seconds. See also timer.
Note that the timer is different from the tick counter. The timer measures elapsed real time in seconds; the tick counter measures elapsed
model time in ticks.
resize-world
Since 4.1
resize-world min-pxcor max-pxcor min-pycor max-pycor
Changes the size of the patch grid.
As a side effect, all turtles and links die, and the existing patch grid is discarded and new patches created.
Retaining references to old patches or patch sets is inadvisable and may subsequently cause runtime errors or other unexpected behavior.
See also set-patch-size.
reverse
Since 1.0
reverse list
reverse string
Reports a reversed copy of the given list or string.
show mylist
;; mylist is [2 7 4 "Bob"]
set mylist reverse mylist
;; mylist now is ["Bob" 4 7 2]
show reverse "live"
=> "evil"
rgb
Since 1.0
rgb red green blue
Reports a RGB list when given three numbers describing an RGB color. The numbers are range checked to be between 0 and 255.
See also hsb
ride
ride turtle
Set the perspective to turtle.
Since 3.0
Every time turtle moves the observer also moves. Thus, in the 2D View the turtle will stay at the center of the view. In the 3D view it is as if
looking through the eyes of the turtle. If the turtle dies, the perspective resets to the default.
The observer may only watch or follow a single subject. Calling ride will remove the highlight created by prior calls to watch and watch-me ,
highlighting the ridden turtle instead.
See also reset-perspective, watch, follow, subject.
ride-me
Since 3.0
ride-me
Asks the observer to ride this turtle.
The observer may only watch or follow a single subject. Calling ride-me will remove the highlight created by prior calls to watch and watch-me ,
highlighting this turtle instead.
See also ride.
right
rt
Since 1.0
Since 1.0
right number
The turtle turns right by number degrees. (If number is negative, it turns left.)
round
Since 1.0
round number
Reports the integer nearest to number.
If the decimal portion of number is exactly .5, the number is rounded in the positive direction.
Note that rounding in the positive direction is not always how rounding is done in other software programs. (In particular, it does not match
the behavior of StarLogoT, which always rounded numbers ending in 0.5 to the nearest even integer.) The rationale for this behavior is that it
matches how turtle coordinates relate to patch coordinates in NetLogo. For example, if a turtle's xcor is -4.5, then it is on the boundary
between a patch whose pxcor is -4 and a patch whose pxcor is -5, but the turtle must be considered to be in one patch or the other, so the
turtle is considered to be in the patch whose pxcor is -4, because we round towards the positive numbers.
show round 4.2
=> 4
show round 4.5
=> 5
show round -4.5
=> -4
See also precision, ceiling, floor.
run
runresult
Since 1.3
Since 1.3
run command
(run command input1 ...)
run string
runresult reporter
(runresult reporter input1 ...)
runresult string
The run form expects the name of a command, an anonymous command, or a string containing commands. This agent then runs them.
The runresult form expects the name of a reporter, an anonymous reporter, or a string containing a reporter. This agent runs it and reports
the result.
Note that you can't use run to define or redefine procedures. If you care about performance, note that the code must be compiled first which
takes time. However, compiled bits of code are cached by NetLogo and thus using run on the same string over and over is much faster than
running different strings. The first run, though, will be many times slower than running the same code directly, or in an anonymous command.
Anonymous procedures are recommended over strings whenever possible. (An example of when you must use strings is if you accept
pieces of code from the user of your model.)
Anonymous procedures may freely read and/or set local variables and procedure inputs. Trying to do the same with strings may or may not
work and should not be relied on.
When using anonymous procedures, you can provide them with inputs, if you surround the entire call with parentheses. For example:
(run [ [turtle-count step-count] -> crt turtle-count [ fd step-count ] ] 10 5)
;; creates 10 turtles and move them forward 5 steps
show (runresult [ [a b] -> a + b ] 10 5)
=> 15
;; adds 10 and 5
See also foreach, -> (anonymous procedure).
S
scale-color
Since 1.0
scale-color color number range1 range2
Reports a shade of color proportional to the value of number.
If range1 is less than range2, then the larger the number, the lighter the shade of color. But if range2 is less than range1, the color scaling is
inverted.
If number is less than range1, then the darkest shade of color is chosen.
If number is greater than range2, then the lightest shade of color is chosen.
Note: for color shade is irrelevant, e.g. green and green + 2 are equivalent, and the same spectrum of colors will be used.
ask turtles [ set color scale-color red age 0 50 ]
;; colors each turtle a shade of red proportional
;; to its value for the age variable
self
Since 1.3
self
Reports this turtle, patch, or link.
"self" and "myself" are very different. "self" is simple; it means "me". "myself" means "the agent who asked me to do what I'm doing right
now."
Note that it is always redundant to write [foo] of self . This is always equivalent to simply writing foo.
See also myself.
; (semicolon)
; comments
After a semicolon, the rest of the line is ignored. This is useful for adding "comments" to your code -- text that explains the code to human
readers. Extra semicolons can be added for visual effect.
NetLogo's Edit menu has items that let you comment or uncomment whole sections of code.
sentence
se
Since 1.0
Since 1.0
sentence value1 value2
(sentence value1 ...)
Makes a list out of the values. If any value is a list, its items are included in the result directly, rather than being included as a sublist.
Examples make this clearer:
show sentence 1 2
=> [1 2]
show sentence [1 2] 3
=> [1 2 3]
show sentence 1 [2 3]
=> [1 2 3]
show sentence [1 2] [3 4]
=> [1 2 3 4]
show sentence [[1 2]] [[3 4]]
=> [[1 2] [3 4]]
show (sentence [1 2] 3 [4 5] (3 + 3) 7)
=> [1 2 3 4 5 6 7]
set
Since 1.0
set variable value
Sets variable to the given value.
Variable can be any of the following:
A global variable declared using "globals"
The global variable associated with a slider, switch, chooser, or input box.
A variable belonging to this agent
If this agent is a turtle, a variable belonging to the patch under the turtle.
A local variable created by the let command.
An input to the current procedure.
set-current-directory
Since 2.0
set-current-directory string
Sets the current directory that is used by the primitives file-delete, file-exists?, and file-open.
The current directory is not used if the above commands are given an absolute file path. This is defaulted to the user's home directory for
new models, and is changed to the model's directory when a model is opened.
Note that in Windows file paths the backslash needs to be escaped within a string by using another backslash "C:\\"
The change is temporary and is not saved with the model.
set-current-directory "C:\\NetLogo"
;; Assume it is a Windows Machine
file-open "my-file.txt"
;; Opens file "C:\\NetLogo\\my-file.txt"
set-current-plot
Since 1.0
set-current-plot plotname
Sets the current plot to the plot with the given name (a string). Subsequent plotting commands will affect the current plot.
set-current-plot-pen
Since 1.0
set-current-plot-pen penname
The current plot's current pen is set to the pen named penname (a string). If no such pen exists in the current plot, a runtime error occurs.
set-default-shape
Since 1.0
set-default-shape turtles string
set-default-shape links string
set-default-shape breed string
Specifies a default initial shape for all turtles or links, or for a particular breed of turtles or links. When a turtle or link is created, or it changes
breeds, it shape is set to the given shape.
This command doesn't affect existing agents, only agents you create afterwards.
The given breed must be either turtles, links, or the name of a breed. The given string must be the name of a currently defined shape.
In new models, the default shape for all turtles is "default".
Note that specifying a default shape does not prevent you from changing an agent's shape later. Agents don't have to be stuck with their
breed's default shape.
create-turtles 1 ;; new turtle's shape is "default"
create-cats 1
;; new turtle's shape is "default"
set-default-shape turtles "circle"
create-turtles 1 ;; new turtle's shape is "circle"
create-cats 1
;; new turtle's shape is "circle"
set-default-shape cats "cat"
set-default-shape dogs "dog"
create-cats 1
;; new turtle's shape is "cat"
ask cats [ set breed dogs ]
;; all cats become dogs, and automatically
;; change their shape to "dog"
See also shape.
set-histogram-num-bars
Since 1.0
set-histogram-num-bars number
Set the current plot pen's plot interval so that, given the current x range for the plot, there would be number number of bars drawn if the
histogram command is called.
See also histogram.
__set-line-thickness
__set-line-thickness number
Specifies the thickness of lines and outlined elements in the turtle's shape.
The default value is 0. This always produces lines one pixel thick.
Non-zero values are interpreted as thickness in patches. A thickness of 1, for example, produces lines which appear one patch thick. (It's
common to use a smaller value such as 0.5 or 0.2.)
Lines are always at least one pixel thick.
This command is experimental and may change in later releases.
set-patch-size
Since 4.1
set-patch-size size
Sets the size of the patches of the view in pixels. The size is typically an integer, but may also be a floating point number.
See also patch-size, resize-world.
set-plot-pen-color
Since 1.0
set-plot-pen-color color
Sets the color of the current plot pen to color.
set-plot-pen-interval
Since 1.0
set-plot-pen-interval number
Tells the current plot pen to move a distance of number in the x direction during each use of the plot command. (The plot pen interval also
affects the behavior of the histogram command.)
set-plot-pen-mode
Since 1.0
set-plot-pen-mode number
Sets the mode the current plot pen draws in to number. The allowed plot pen modes are:
0 (line mode) the plot pen draws a line connecting two points together.
1 (bar mode): the plot pen draws a bar of width plot-pen-interval with the point plotted as the upper (or lower, if you are plotting a negative
number) left corner of the bar.
2 (point mode): the plot pen draws a point at the point plotted. Points are not connected.
The default mode for new pens is 0 (line mode).
setup-plots
Since 5.0
setup-plots
For each plot, runs that plot's setup commands, including the setup code for any pens in the plot.
reset-ticks has the same effect, so in models that use the tick counter, this primitive is not normally used.
See the Plotting section of the Programming Guide for more details.
See also update-plots.
set-plot-x-range
set-plot-y-range
Since 1.0
Since 1.0
set-plot-x-range min max
set-plot-y-range min max
Sets the minimum and maximum values of the x or y axis of the current plot.
The change is temporary and is not saved with the model. When the plot is cleared, the ranges will revert to their default values as set in the
plot's Edit dialog.
setxy
Since 1.0
setxy x y
The turtle sets its x-coordinate to x and its y-coordinate to y.
Equivalent to set xcor x set ycor y, except it happens in one time step instead of two.
If x or y is outside the world, NetLogo will throw a runtime error, unless wrapping is turned on in the relevant dimensions. For example, with
wrapping turned on in both dimensions and the default world size where min-pxcor = -16 , max-pxcor = 16 , min-pycor = -16 and max-pycor =
16 , asking a turtle to setxy 17 17 will move it to the center of patch (-16, -16).
setxy 0 0
;; turtle moves to the middle of the center patch
setxy random-xcor random-ycor
;; turtle moves to a random point
setxy random-pxcor random-pycor
;; turtle moves to the center of a random patch
See also move-to.
shade-of?
Since 1.0
shade-of? color1 color2
Reports true if both colors are shades of one another, false otherwise.
show shade-of? blue red
=> false
show shade-of? blue (blue + 1)
=> true
show shade-of? gray white
=> true
shape
shape
This is a built-in turtle and link variable. It holds a string that is the name of the turtle or link's current shape. You can set this variable to
change the shape. New turtles and links have the shape "default" unless the a different shape has been specified using set-default-shape.
Example:
ask turtles [ set shape "wolf" ]
;; assumes you have made a "wolf"
;; shape in NetLogo's Turtle Shapes Editor
ask links [ set shape "link 1" ]
;; assumes you have made a "link 1" shape in
;; the Link Shapes Editor
See also set-default-shape, shapes.
shapes
Since 2.1
shapes
Reports a list of strings containing all of the turtle shapes in the model.
New shapes can be created, or imported from the shapes library or from other models, in the Shapes Editor.
show shapes
=> ["default" "airplane" "arrow" "box" "bug" ...
ask turtles [ set shape one-of shapes ]
show
Since 1.0
show value
Prints value in the Command Center, preceded by this agent, and followed by a carriage return. (This agent is included to help you keep track
of what agents are producing which lines of output.) Also, all strings have their quotes included similar to write.
See also print, type, and write.
See also output-show.
show-turtle
st
Since 1.0
Since 1.0
show-turtle
The turtle becomes visible again.
Note: This command is equivalent to setting the turtle variable "hidden?" to false.
See also hide-turtle.
show-link
show-link
The link becomes visible again.
Note: This command is equivalent to setting the link variable "hidden?" to false.
Since 4.0
See also hide-link.
shuffle
Since 2.0
shuffle list
Reports a new list containing the same items as the input list, but in randomized order.
show shuffle [1 2 3 4 5]
=> [5 2 4 1 3]
show shuffle [1 2 3 4 5]
=> [1 3 5 2 4]
sin
Since 1.0
sin number
Reports the sine of the given angle. Assumes angle is given in degrees.
show sin 270
=> -1
size
size
This is a built-in turtle variable. It holds a number that is the turtle's apparent size. The default size is 1, which means that the turtle is the
same size as a patch. You can set this variable to change a turtle's size.
sort
Since 1.0
sort list
sort agentset
Reports a sorted list of numbers, strings, or agents.
If the input contains no numbers, strings, or agents, the result is the empty list.
If the input contains at least one number, the numbers in the list are sorted in ascending order and a new list reported; non-numbers are
ignored.
Or, if the input contains at least one string, the strings in the list are sorted in ascending order and a new list reported; non-strings are
ignored.
Or, if the input is an agentset or a list containing at least one agent, a sorted list of agents (never an agentset) is reported; non-agents are
ignored. Agents are sorted in the same order the < operator uses. (Patches are sorted with the top left-most patch first and the bottom rightmost patch last, turtles are sorted by who number).
show sort [3 1 4 2]
=> [1 2 3 4]
show sort [2 1 "a"]
=> [1 2]
show sort (list "a" "c" "b" (patch 0 0))
=> ["a" "b" "c"]
show sort (list (patch 0 0) (patch 0 1) (patch 1 0))
=> [(patch 0 1) (patch 0 0) (patch 1 0)]
;; label patches with numbers in left-to-right, top-to-bottom order
let n 0
foreach sort patches [ the-patch ->
ask the-patch [
set plabel n
set n n + 1
]
]
;; some additional examples to clarify behavior in strange cases
show sort (list patch 0 0 patch 0 1 patch 1 0 turtle 0 turtle 1) ; turtles are always sorted lower than patches
=> [(turtle 0) (turtle 1) (patch 0 1) (patch 0 0) (patch 1 0)]
show sort (list nobody false true) ; booleans and nobody cannot be sorted
=> []
show sort (list [1 2 3] turtles) ; lists and agentsets are not included if they are inside a list passed to sort
=> []
See also sort-by, sort-on.
sort-by
Since 1.3
sort-by reporter list
sort-by reporter agentset
If the input is a list, reports a new list containing the same items as the input list, in a sorted order defined by the boolean reporter. reporter
may be an anonymous reporter or the name of a reporter.
The two inputs to reporter are the values being compared. The reporter should report true if the first argument comes strictly before the
second in the desired sort order, and false otherwise.
If the input is an agentset or a list of agents, reports a list (never an agentset) of agents.
If the input is a list, the sort is stable, that is, the order of items considered equal by the reporter is not disturbed. If the input is an agentset,
ties are broken randomly.
show sort-by < [3 1 4 2]
=> [1 2 3 4]
show sort-by > [3 1 4 2]
=> [4 3 2 1]
show sort-by [ [string1 string2] -> length string1 < length string2 ] ["Grumpy" "Doc" "Happy"]
=> ["Doc" "Happy" "Grumpy"]
See also sort, sort-on, -> (anonymous procedure).
sort-on
Since 5.0
sort-on [reporter] agentset
Reports a list of agents, sorted according to each agent's value for reporter. Ties are broken randomly.
The values must be all numbers, all strings, or all agents of the same type.
crt 3
show sort-on [who] turtles
=> [(turtle 0) (turtle 1) (turtle 2)]
show sort-on [(- who)] turtles
=> [(turtle 2) (turtle 1) (turtle 0)]
foreach sort-on [size] turtles
[ the-turtle -> ask the-turtle [ do-something ] ]
;; turtles run "do-something" one at a time, in
;; ascending order by size
See also sort, sort-by.
sprout
Since 1.0
sprout number [ commands ]
sprout- number [ commands ]
Creates number new turtles on the current patch. The new turtles have random integer headings and the color is randomly selected from the
14 primary colors. The turtles immediately run commands. This is useful for giving the new turtles different colors, headings, or whatever.
(The new turtles are created all at once then run one at a time, in random order.)
If the sprout- form is used, the new turtles are created as members of the given breed.
sprout 5
sprout-wolves 10
sprout 1 [ set color red ]
sprout-sheep 1 [ set color black ]
See also create-turtles, hatch.
sqrt
Since 1.0
sqrt number
Reports the square root of number.
stamp
Since 1.0
stamp
This turtle or link leaves an image of its shape in the drawing at its current location.
Note: The shapes made by stamp may not be pixel-for-pixel identical from computer to computer.
stamp-erase
Since 3.1
stamp-erase
This turtle or link removes any pixels below it in the drawing inside the bounds of its shape.
Note: The shapes made by stamp-erase may not be pixel-for-pixel identical from computer to computer.
standard-deviation
standard-deviation list
Since 1.0
Reports the sample standard deviation of a list of numbers. Ignores other types of items.
(Note that this estimates the standard deviation for a sample, rather than for a whole population, using Bessel's correction.)
show standard-deviation [1 2 3 4 5 6]
=> 1.8708286933869707
show standard-deviation [energy] of turtles
;; prints the standard deviation of the variable "energy"
;; from all the turtles
startup
startup
User-defined procedure which, if it exists, will be called when a model is first loaded in the NetLogo application.
to startup
setup
end
startup
does not run when a model is run headless from the command line, or by parallel BehaviorSpace.
stop
Since 1.0
stop
This agent exits immediately from the enclosing procedure, ask, or ask-like construct (e.g. crt, hatch, sprout). Only the enclosing procedure or
construct stops, not all execution for the agent.
if not any? turtles [ stop ]
;; exits if there are no more turtles
Note: stop can also be used to stop a forever button. See Buttons in the Programming Guide for details.
can also be used to stop a BehaviorSpace model run. If the go commands directly call a procedure, then when that procedure calls stop,
the run ends.
stop
stop-inspecting
Since 5.2
stop-inspecting agent
Closes the agent monitor for the given agent (turtle or patch). In the case that no agent monitor is open, stop-inspecting does nothing.
stop-inspecting patch 2 4
;; the agent monitor for that patch closes
ask sheep [ stop-inspecting self ]
;; close all agent monitors for sheep
See inspect and stop-inspecting-dead-agents.
stop-inspecting-dead-agents
Since 5.2
stop-inspecting-dead-agents
Closes all agent monitors for dead agents. See inspect and stop-inspecting.
subject
Since 3.0
subject
Reports the turtle (or patch) that the observer is currently watching, following, or riding. Reports nobody if there is no such turtle (or patch).
See also watch, follow, ride.
sublist
substring
sublist list position1 position2
substring string position1 position2
Reports just a section of the given list or string, ranging between the first position (inclusive) and the second position (exclusive).
Note: The positions are numbered beginning with 0, not with 1.
show sublist [99 88 77 66] 1 3
=> [88 77]
show substring "apartment" 1 5
=> "part"
Since 2.1
Since 1.0
subtract-headings
Since 2.1
subtract-headings heading1 heading2
Computes the difference between the given headings, that is, the number of degrees in the smallest angle by which heading2 could be
rotated to produce heading1. A positive answer means a clockwise rotation, a negative answer counterclockwise. The result is always in the
range -180 to 180, but is never exactly -180.
Note that simply subtracting the two headings using the - (minus) operator wouldn't work. Just subtracting corresponds to always rotating
clockwise from heading2 to heading1; but sometimes the counterclockwise rotation is shorter. For example, the difference between 5
degrees and 355 degrees is 10 degrees, not -350 degrees.
show subtract-headings
=> 20
show subtract-headings
=> -20
show subtract-headings
=> 10
show subtract-headings
=> -10
show subtract-headings
=> 180
show subtract-headings
=> 180
80 60
60 80
5 355
355 5
180 0
0 180
sum
Since 1.0
sum list
Reports the sum of the items in the list.
show sum [energy] of turtles
;; prints the total of the variable "energy"
;; from all the turtles
T
tan
Since 1.0
tan number
Reports the tangent of the given angle. Assumes the angle is given in degrees.
thickness
thickness
This is a built-in link variable. It holds a number that is the link's apparent size as a fraction of the patch size. The default thickness is 0, which
means that regardless of patch-size the links will always appear 1 pixel wide. You can set this variable to change a link's thickness.
tick
Since 4.0
tick
Advances the tick counter by one and updates all plots.
If the tick counter has not been started yet with reset-ticks, an error results.
Normally tick goes at the end of a go procedure.
See also ticks, tick-advance, reset-ticks, clear-ticks, update-plots.
tick-advance
Since 4.0
tick-advance number
Advances the tick counter by number. The input may be an integer or a floating point number. (Some models divide ticks more finely than by
ones.) The input may not be negative.
When using tick-based view updates, the view is normally updated every 1.0 ticks, so using tick-advance with a number less then 1.0 may
not always trigger an update. If you want to make sure that the view is updated, you can use the display command.
If the tick counter has not been started yet with reset-ticks, an error results.
Does not update plots.
See also tick, ticks, reset-ticks, clear-ticks.
ticks
Since 4.0
ticks
Reports the current value of the tick counter. The result is always a number and never negative.
If the tick counter has not been started yet with reset-ticks, an error results.
Most models use the tick command to advance the tick counter, in which case ticks will always report an integer. If the tick-advance
command is used, then ticks may report a floating point number.
See also tick, tick-advance, reset-ticks, clear-ticks.
tie
Since 4.0
tie
Ties end1 and end2 of the link together. If the link is a directed link end1 is the root turtle and end2 is the leaf turtle. The movement of the root
turtle affects the location and heading of the leaf turtle. If the link is undirected the tie is reciprocal so both turtles can be considered root
turtles and leaf turtles. Movement or change in heading of either turtle affects the location and heading of the other turtle.
When the root turtle moves, the leaf turtles moves the same distance, in the same direction. The heading of the leaf turtle is not affected.
This works with forward, jump, and setting the xcor or ycor of the root turtle.
When the root turtle turns right or left, the leaf turtle is rotated around the root turtle the same amount. The heading of the leaf turtle is also
changed by the same amount.
If the link dies, the tie relation is removed.
crt 2 [ fd 3 ]
;; creates a link and ties turtle 1 to turtle 0
ask turtle 0 [ create-link-to turtle 1 [ tie ] ]
See also untie
tie-mode
tie-mode
This is a built-in link variable. It holds a string that is the name of the tie mode the link is currently in. Using the tie and untie commands
changes the mode of the link. You can also set tie-mode to "free" to create a non-rigid joint between two turtles (see the Tie section of the
Programming Guide for details). By default links are not tied.
See also: tie, untie
timer
Since 1.0
timer
Reports how many seconds have passed since the command reset-timer was last run (or since NetLogo started). The potential resolution of
the clock is milliseconds. (Whether you get resolution that high in practice may vary from system to system, depending on the capabilities of
the underlying Java Virtual Machine.)
See also reset-timer.
Note that the timer is different from the tick counter. The timer measures elapsed real time in seconds; the tick counter measures elapsed
model time in ticks.
to
to procedure-name
to procedure-name [input1 ...]
Used to begin a command procedure.
to setup
clear-all
crt 500
end
to circle [radius]
crt 100 [ fd radius ]
end
to-report
to-report procedure-name
to-report procedure-name [input1 ...]
Used to begin a reporter procedure.
The body of the procedure should use report to report a value for the procedure. See report.
to-report average [a b]
report (a + b) / 2
end
to-report absolute-value [number]
ifelse number >= 0
[ report number ]
[ report (- number) ]
end
to-report first-turtle?
report who = 0 ;; reports true or false
end
towards
Since 1.0
towards agent
Reports the heading from this agent to the given agent.
If wrapping is allowed by the topology and the wrapped distance (around the edges of the world) is shorter, towards will use the wrapped
path.
Note: asking for the heading from an agent to itself, or an agent on the same location, will cause a runtime error.
set heading towards turtle 1
;; same as "face turtle 1"
See also face.
towardsxy
Since 1.0
towardsxy x y
Reports the heading from the turtle or patch towards the point (x,y).
If wrapping is allowed by the topology and the wrapped distance (around the edges of the world) is shorter, towardsxy will use the wrapped
path.
Note: asking for the heading to the point the agent is already standing on will cause a runtime error.
See also facexy.
turtle
Since 1.0
turtle number
number
Reports the turtle with the given who number, or nobody if there is no such turtle. For breeded turtles you may also use the single breed form
to refer to them.
ask turtle 5 [ set color red ]
;; turtle with who number 5 turns red
turtle-set
Since 4.0
turtle-set value1
(turtle-set value1 value2 ...)
Reports an agentset containing all of the turtles anywhere in any of the inputs. The inputs may be individual turtles, turtle agentsets, nobody,
or lists (or nested lists) containing any of the above.
turtle-set self
(turtle-set self turtles-on neighbors)
(turtle-set turtle 0 turtle 2 turtle 9)
(turtle-set frogs mice)
See also patch-set, link-set.
turtles
turtles
Reports the agentset consisting of all turtles.
show count turtles
;; prints the number of turtles
Since 1.0
turtles-at
Since 1.0
turtles-at dx dy
-at dx dy
Reports an agentset containing the turtles on the patch (dx, dy) from the caller. (The result may include the caller itself if the caller is a turtle.)
create-turtles 5 [ setxy 2 3 ]
show count [turtles-at 1 1] of patch 1 2
=> 5
If the name of a breed is substituted for "turtles", then only turtles of that breed are included.
turtles-here
Since 1.0
turtles-here
-here
Reports an agentset containing all the turtles on the caller's patch (including the caller itself if it's a turtle).
crt 10
ask turtle 0 [ show count turtles-here ]
=> 10
If the name of a breed is substituted for "turtles", then only turtles of that breed are included.
breed [cats cat]
breed [dogs dog]
create-cats 5
create-dogs 1
ask dogs [ show count cats-here ]
=> 5
turtles-on
Since 2.0
turtles-on agent
turtles-on agentset
-on agent
-on agentset
Reports an agentset containing all the turtles that are on the given patch or patches, or standing on the same patch as the given turtle or
turtles.
ask turtles [
if not any? turtles-on patch-ahead 1
[ fd 1 ]
]
ask turtles [
if not any? turtles-on neighbors [
die-of-loneliness
]
]
If the name of a breed is substituted for "turtles", then only turtles of that breed are included.
turtles-own
turtles-own [var1 ...]
-own [var1 ...]
The turtles-own keyword, like the globals, breed, -own, and patches-own keywords, can only be used at the beginning of a program,
before any function definitions. It defines the variables belonging to each turtle.
If you specify a breed instead of "turtles", only turtles of that breed have the listed variables. (More than one turtle breed may list the same
variable.)
breed [cats cat ]
breed [dogs dog]
breed [hamsters hamster]
turtles-own [eyes legs]
cats-own [fur kittens]
hamsters-own [fur cage]
dogs-own [hair puppies]
;; applies to all breeds
See also globals, patches-own, breed, -own.
type
type value
Since 1.0
Prints value in the Command Center, not followed by a carriage return (unlike print and show). The lack of a carriage return allows you to print
several values on the same line.
This agent is not printed before the value. unlike show.
type 3 type " " print 4
=> 3 4
See also print, show, and write.
See also output-type.
U
undirected-link-breed
undirected-link-breed []
This keyword, like the globals and breeds keywords, can only be used at the beginning of the Code tab, before any procedure definitions. It
defines an undirected link breed. Links of a particular breed are always either all directed or all undirected. The first input defines the name of
the agentset associated with the link breed. The second input defines the name of a single member of the breed.
Any link of the given link breed:
is part of the agentset named by the link breed name
has its built-in variable breed set to that agentset
is directed or undirected as declared by the keyword
Most often, the agentset is used in conjunction with ask to give commands to only the links of a particular breed.
undirected-link-breed [streets street]
undirected-link-breed [highways highway]
to setup
clear-all
crt 2
ask turtle 0 [ create-street-with turtle 1 ]
ask turtle 0 [ create-highway-with turtle 1 ]
end
ask turtle 0 [ show sort my-links ]
;; prints [(street 0 1) (highway 0 1)]
See also breed, directed-link-breed
untie
Since 4.0
untie
Unties end2 from end1 (sets tie-mode to "none") if they were previously tied together. If the link is an undirected link, then it will untie end1
from end2 as well. It does not remove the link between the two turtles.
See also tie
See the Tie section of the Programming Guide for more details.
update-plots
Since 5.0
update-plots
For each plot, runs that plot's update commands, including the update code for any pens in the plot.
tick has the same effect, so in models that use the tick counter, this primitive is not normally used. Models that use fractional ticks may need
update-plots , since tick-advance does not update the plots.
See the Plotting section of the Programming Guide for more details.
See also setup-plots.
uphill
uphill4
Since 1.0
Since 1.0
uphill patch-variable
uphill4 patch-variable
Moves the turtle to the neighboring patch with the highest value for patch-variable. If no neighboring patch has a higher value than the current
patch, the turtle stays put. If there are multiple patches with the same highest value, the turtle picks one randomly. Non-numeric values are
ignored.
uphill considers the eight neighboring patches; uphill4 only considers the four neighbors.
Equivalent to the following code (assumes variable values are numeric):
move-to patch-here ;; go to patch center
let p max-one-of neighbors [patch-variable]
if [patch-variable] of p > patch-variable [
face p
move-to p
]
;; or neighbors4
Note that the turtle always ends up on a patch center and has a heading that is a multiple of 45 (uphill) or 90 (uphill4).
See also downhill, downhill4.
user-directory
Since 3.1
user-directory
Opens a dialog that allows the user to choose an existing directory on the system.
It reports a string with the absolute path or false if the user cancels.
set-current-directory user-directory
;; Assumes the user will choose a directory
user-file
Since 3.1
user-file
Opens a dialog that allows the user to choose an existing file on the system.
It reports a string with the absolute file path or false if the user cancels.
file-open user-file
;; Assumes the user will choose a file
user-new-file
Since 3.1
user-new-file
Opens a dialog that allows the user to choose a location and name of a new file to be created. It reports a string with the absolute file path or
false if the user cancels.
file-open user-new-file
;; Assumes the user will choose a file
Note that this reporter doesn't actually create the file; normally you would create the file using file-open, as in the example.
If the user chooses an existing file, they will be asked if they wish to replace it or not, but the reporter itself doesn't cause the file to be
replaced. To do that you would use file-delete.
user-input
Since 1.1
user-input value
Reports the string that a user types into an entry field in a dialog with title value.
value may be of any type, but is typically a string.
show user-input "What is your name?"
See the User Interaction Primitives section of the Programming Guide for additional details.
user-message
Since 1.1
user-message value
Opens a dialog with value displayed as the message to the user.
value may be of any type, but is typically a string.
user-message (word "There are " count turtles " turtles.")
Note that if a user closes the user-message dialog with the "X" in the corner, the behavior will be the same as if they had clicked "OK".
See the User Interaction Primitives section of the Programming Guide for additional details.
user-one-of
user-one-of value list-of-choices
Since 3.1
Opens a dialog with value displayed as the message and list-of-choices displayed as a popup menu for the user to select from.
Reports the item in list-of-choices selected by the user.
value may be of any type, but is typically a string.
if "yes" = user-one-of "Set up the model?" ["yes" "no"]
[ setup ]
See the User Interaction Primitives section of the Programming Guide for additional details.
user-yes-or-no?
Since 2.0
user-yes-or-no? value
Reports true or false based on the user's response to value.
value may be of any type, but is typically a string.
if user-yes-or-no? "Set up the model?"
[ setup ]
See the User Interaction Primitives section of the Programming Guide for additional details.
V
variance
Since 1.0
variance list
Reports the sample variance of a list of numbers. Ignores other types of items.
(Note that this computes an unbiased estimate of the variance for a sample, rather than for a whole population, using Bessel's correction.)
The sample variance is the sum of the squares of the deviations of the numbers from their mean, divided by one less than the number of
numbers in the list.
show variance [2 7 4 3 5]
=> 3.7
W
wait
Since 1.0
wait number
Wait the given number of seconds. (This needn't be an integer; you can specify fractions of seconds.) Note that you can't expect complete
precision; the agent will never wait less than the given amount, but might wait slightly more.
repeat 10 [ fd 1 wait 0.5 ]
While the agent is waiting, no other agents can do anything. Everything stops until the agent is done.
See also every.
watch
Since 3.0
watch agent
Puts a spotlight on agent. In the 3D view the observer will also turn to face the subject.
The observer may only watch or follow a single subject. Calling watch will undo perspective changes caused by prior calls to follow, followme , ride, and ride-me .
See also follow, subject, reset-perspective, ride, ride-me, watch-me.
watch-me
Since 3.0
watch-me
Asks the observer to watch this agent.
The observer may only watch or follow a single subject. Calling watch will undo perspective changes caused by prior calls to follow, followme , ride, and ride-me .
See also follow, subject, reset-perspective, ride, ride-me, watch.
while
Since 1.0
while [reporter] [ commands ]
If reporter reports false, exit the loop. Otherwise run commands and repeat.
The reporter may have different values for different agents, so some agents may run commands a different number of times than other
agents.
while [any? other turtles-here]
[ fd 1 ]
;; turtle moves until it finds a patch that has
;; no other turtles on it
who
who
This is a built-in turtle variable. It holds the turtle's "who number" or ID number, an integer greater than or equal to zero. You cannot set this
variable; a turtle's who number never changes.
Who numbers start at 0. A dead turtle's number will not be reassigned to a new turtle until you use the clear-turtles or clear-all commands, at
which time who numbering starts over again at 0.
Example:
show [who] of turtles with [color = red]
;; prints a list of the who numbers of all red turtles
;; in the Command Center, in random order
crt 100
[ ifelse who < 50
[ set color red ]
[ set color blue ] ]
;; turtles 0 through 49 are red, turtles 50
;; through 99 are blue
You can use the turtle reporter to retrieve a turtle with a given who number. See also turtle.
Note that who numbers aren't breed-specific. No two turtles can have the same who number, even if they are different breeds:
clear-turtles
create-frogs 1
create-mice 1
ask turtles [ print who ]
;; prints (in some random order):
;; (frog 0): 0
;; (mouse 1): 1
Even though we only have one mouse, it is mouse 1 not mouse 0 , because the who number 0 was already taken by the frog.
with
Since 1.0
agentset with [reporter]
Takes two inputs: on the left, an agentset (usually "turtles" or "patches"). On the right, a boolean reporter. Reports a new agentset containing
only those agents that reported true -- in other words, the agents satisfying the given condition.
show count patches with [pcolor = red]
;; prints the number of red patches
-with
link-with
Since 4.0
-with turtle
link-with turtle
Reports a link between turtle and the caller (directed or undirected, incoming or outgoing). If no link exists then it reports nobody. If more than
one such link exists, reports a random one.
crt 2
ask turtle 0 [
create-link-with turtle 1
show link-with turtle 1 ;; prints link 0 1
]
See also: in-link-from, out-link-to
with-max
agentset with-max [reporter]
Since 2.1
Takes two inputs: on the left, an agentset (usually "turtles" or "patches"). On the right, a reporter. Reports a new agentset containing all
agents reporting the maximum value of the given reporter.
show count patches with-max [pxcor]
;; prints the number of patches on the right edge
See also max-one-of, max-n-of.
with-min
Since 2.1
agentset with-min [reporter]
Takes two inputs: on the left, an agentset (usually "turtles" or "patches"). On the right, a reporter. Reports a new agentset containing only
those agents that have the minimum value of the given reporter.
show count patches with-min [pycor]
;; prints the number of patches on the bottom edge
See also min-one-of, min-n-of.
with-local-randomness
Since 4.0
with-local-randomness [ commands ]
The commands are run without affecting subsequent random events. This is useful for performing extra operations (such as output) without
changing the outcome of a model.
Example:
;; Run #1:
random-seed 50 setup repeat 10 [ go ]
;; Run #2:
random-seed 50 setup
with-local-randomness [ watch one-of turtles ]
repeat 10 [ go ]
Since one-of is used inside with-local-randomness, both runs will be identical.
Specifically how it works is, the state of the random number generator is remembered before the commands run, then restored afterwards. (If
you want to run the commands with a fresh random state instead of the same random state that will be restored later, you can begin the
commands with random-seed new-seed.)
The following example demonstrates that the random number generator state is the same both before the commands run and afterwards.
random-seed 10
with-local-randomness [ print n-values 10 [random 10] ]
;; prints [8 9 8 4 2 4 5 4 7 9]
print n-values 10 [random 10]
;; prints [8 9 8 4 2 4 5 4 7 9]
without-interruption
Since 1.1
without-interruption [ commands ]
This primitive exists only for backwards compatibility. We don't recommend using it in new models.
The agent runs all the commands in the block without allowing other agents using ask-concurrent to "interrupt". That is, other agents are put
"on hold" and do not run any commands until the commands in the block are finished.
Note: This command is only useful in conjunction with ask-concurrent.
See also ask-concurrent.
word
word value1 value2
(word value1 ...)
Concatenates the inputs together and reports the result as a string.
show word "tur" "tle"
=> "turtle"
word "a" 6
=> "a6"
set directory "c:\\foo\\fish\\"
show word directory "bar.txt"
=> "c:\foo\fish\bar.txt"
show word [1 54 8] "fishy"
=> "[1 54 8]fishy"
show (word 3)
=> "3"
show (word "a" "b" "c" 1 23)
=> "abc123"
Since 1.0
world-width
world-height
Since 3.1
Since 3.1
world-width
world-height
These reporters give the total width and height of the NetLogo world.
The width equals max-pxcor - min-pxcor + 1 and the height equals max-pycor - min-pycor + 1.
See also max-pxcor, max-pycor, min-pxcor, and min-pycor
wrap-color
Since 1.0
wrap-color number
wrap-color checks whether number is in the NetLogo color range of 0 to 140 (not including 140 itself). If it is not, wrap-color "wraps" the
numeric input to the 0 to 140 range.
The wrapping is done by repeatedly adding or subtracting 140 from the given number until it is in the 0 to 140 range. (This is the same
wrapping that is done automatically if you assign an out-of-range number to the color turtle variable or pcolor patch variable.)
show wrap-color 150
=> 10
show wrap-color -10
=> 130
write
Since 2.0
write value
This command will output value, which can be a number, string, list, boolean, or nobody to the Command Center, not followed by a carriage
return (unlike print and show).
This agent is not printed before the value, unlike show. Its output also includes quotes around strings and is prepended with a space.
write "hello world"
=> "hello world"
See also print, show, and type.
See also output-write.
X
xcor
xcor
This is a built-in turtle variable. It holds the current x coordinate of the turtle. You can set this variable to change the turtle's location.
This variable is always greater than or equal to (min-pxcor - 0.5) and strictly less than (max-pxcor + 0.5).
See also setxy, ycor, pxcor, pycor,
xor
Since 1.0
boolean1 xor boolean2
Reports true if either boolean1 or boolean2 is true, but not when both are true.
if (pxcor > 0) xor (pycor > 0)
[ set pcolor blue ]
;; upper-left and lower-right quadrants turn blue
Y
ycor
ycor
This is a built-in turtle variable. It holds the current y coordinate of the turtle. You can set this variable to change the turtle's location.
This variable is always greater than or equal to (min-pycor - 0.5) and strictly less than (max-pycor + 0.5).
See also setxy, xcor, pxcor, pycor,
->
->
Since 6.0
[ [args] -> commands ]
[ [args] -> reporter ]
Creates and reports an anonymous procedure - a command or reporter - depending on the input. Within commands or reporter the listed args
may be used just as you would use let or procedure variables. The variable names in args have the same restrictions as variable names of
commands and reporters. In addition, they must not match the name of any let or procedure variable in their procedure.
Anonymous procedures are commonly used with the primitives foreach, map, reduce, filter, sort-by, and n-values. See those entries for
example usage.
See the Anonymous Procedures section of the Programming Guide for details.
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