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.

abs

abs number

Reports the absolute value of number.

show abs -7
=> 7
show abs 5
=> 5

acos

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?

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.

The reporter must report a boolean value for every agent tested (either true or false), otherwise an error occurs.

if all? turtles [color = red]
  [ show "every turtle is red!" ]

See also any?.

and

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?

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

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.

All three values 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. (It contains only certain discrete hues, and for each hue, either saturation or brightness may vary, but not both -- at least one of the two is always 255.)

show approximate-hsb 0 0 0
=> 0  ;; (black)
show approximate-hsb 127.5 255 255
=> 85.2 ;; (cyan)

See also extract-hsb, approximate-rgb, extract-rgb.

approximate-rgb

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 (+, *, -, /, ^, <, >, =, !=, <=, >=)

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 Procedures 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

asin

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

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

ask-concurrent agentset [commands]

The agents in the given agentset run the given commands, using a turn-taking mechanism to produce simulated concurrency. See the Ask-Concurrent 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

agentset at-points [[x1 y1] [x2 y2] ...]

Reports a subset of the given agentset that includes only the agents on the patches the given distances away from the calling agent. The distances 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
            ;; distances (2,4), (1,2) and (10,15),
            ;; relative to the caller, move

atan

atan x y

Reports the arc tangent, in degrees (from 0 to 360), of x divided by y.

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.

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.)

show atan 1 -1
=> 135
show atan -1 1
=> 315

autoplot?

autoplot?

Reports true if auto-plotting is on for the current plot, false otherwise.

auto-plot-off
auto-plot-on

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.

back
bk

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

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

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                       ;; emits one beep
repeat 3 [ beep ]          ;; emits 3 beeps at once,
                           ;; so you only hear one sound
repeat 3 [ beep wait 0.1 ] ;; produces 3 beeps in succession, 
                           ;; separated by 1/10th of a second

both-ends

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.

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 [<breeds> <breed>]

This keyword, like the globals, turtles-own, and patches-own keywords, can only be used at the beginning of the Procedures 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    ;; prints mice
  show [breed] of one-of frogs   ;; prints frogs
end

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, <breeds>-own, create-<breeds>, <breeds>-at, <breeds>-here.

but-first
bf
but-last
bl

but-first list
but-first string
but-last list
but-last string

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"

can-move?

can-move? distance

Reports true if the calling 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

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.

Note: both sets of commands run without interruption (as with the without-interruption command).

carefully [ show 1 / 1 ] [ print error-message ]
=> 1
carefully [ show 1 / 0 ] [ print error-message ]
=> division by zero

ceiling

ceiling number

Reports the smallest integer greater than or equal to number.

show ceiling 4.5
=> 5
show ceiling -4.5
=> -4

clear-all
ca

clear-all

Resets all global variables to zero, and calls reset-ticks, clear-turtles, clear-patches, clear-drawing, clear-all-plots, and clear-output.

clear-all-plots

clear-all-plots

Clears every plot in the model. See clear-plot for more information.

clear-drawing
cd

clear-drawing

Clears all lines and stamps drawn by turtles.

clear-links

clear-links

Kills all links.

See also die.

clear-output

clear-output

Clears all text from the model's output area, if it has one. Otherwise does nothing.

clear-patches
cp

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-turtles
ct

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

cos number

Reports the cosine of the given angle. Assumes the angle is given in degrees.

show cos 180
=> -1

count

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
create-ordered-<breeds>

create-ordered-turtles number
create-ordered-turtles number [ commands ]
create-ordered<breeds> number
create-ordered<breeds> 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-<breeds> 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

Note: While the commands are running, no other agents are allowed to run any code (as with the without-interruption command). This ensures that if ask-concurrent is being used, the new turtles cannot interact with any other agents until they are fully initialized.

create-<breed>-to
create-<breeds>-to
create-<breed>-from
create-<breeds>-from
create-<breed>-with
create-<breeds>-with
create-link-to
create-links-to
create-link-from
create-links-from
create-link-with
create-links-with

create-<breed>-to turtle
create-<breed>-to turtle [ commands ]
create-<breed>-from turtle
create-<breed>-from turtle [ commands ]
create-<breed>-with turtle
create-<breed>-with turtle [ commands ]
create-<breeds>-to turtleset
create-<breeds>-to turtleset [ commands ]
create-<breeds>-from turtleset
create-<breeds>-from turtleset [ commands ]
create-<breeds>-with turtleset
create-<breeds>-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 ]

Used for creating breeded and unbreeded links between turtles.

create-link-with creates an undirected link between the caller and agent. create-link-to creates a directed link from the caller to agent. create-link-from 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
   crt 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
  crt 5
  ;; create links in both directions between turtle 0
  ;; and all other turtles
  ask turtle 0 [ create-red-links-to turtles ]
  ask turtle 0 [ create-red-links-from turtles ]
  show count links ;; shows 8
  ;; now create undirected links between turtle 0 and other turtles
  ask turtle 0 [ create-blue-links-with turtles ]
  show count links ;; shows 12
end

create-turtles
crt
create-<breeds>

create-turtles number
create-turtles number [ commands ]
create-<breeds> number
create-<breeds> number [ commands ]

Creates number new turtles . New turtles have random integer headings and the color is randomly selected from the 14 primary colors.

If the create-<breeds> 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

Note: While the commands are running, no other agents are allowed to run any code (as with the without-interruption command). This ensures that if ask-concurrent is being used, the new turtles cannot interact with any other agents until they are fully initialized.

See also hatch, sprout.

create-temporary-plot-pen

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 temporary pen with that name already exists in the current plot, no new pen is created, and the existing pen is set to the the current pen. If a permanent pen with that name already exists in the current plot, you get a runtime error.

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.

date-and-time

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

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 blue links die

See also: clear-turtles clear-links

diffuse

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

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 [<link-breeds> <link-breed>]

This keyword, like the globals and breeds keywords, can only be used at the beginning of the Procedures 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 in-links ]
;; prints (street 0 1)
ask turtle 0 [ show one-of out-links ]
;; prints (highway 1 0)

See also breed, undirected-link-breed

display

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

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

distancexy xcor ycor

Reports the distance from this agent to the point (xcor, ycor).

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

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]  ;; or neighbors4
if [patch-variable] of p < patch-variable [
  face p
  move-to p
]

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

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.

empty?

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

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

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-message

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 carefully.

every

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

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

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.

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 the file already exists, it is overwritten.

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

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

extract-hsb color

Reports a list of three values in the range 0 to 255 representing the hue, saturation and brightness, respectively, of the given NetLogo color in the range 0 to 140, not including 140 itself.

show extract-hsb red
=> [2.198 206.372 215]
show extract-hsb cyan
=> [127.5 145.714 196]

See also approximate-hsb, approximate-rgb, extract-rgb.

extract-rgb

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.

face

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

facexy number number

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?

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

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

file-close-all

Closes all files (if any) that have been opened previously with file-open.

See also file-close, file-open.

file-delete

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?

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

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

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 file-read-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

See also file-close.

file-print

file-print value

Prints value to an opened file, followed by a carriage return.

The calling 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

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

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

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

file-show value

Prints value to an opened file, preceded by the calling agent, and followed by a carriage return. (The calling 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

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.

The calling 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

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).

The calling 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

filter [reporter] list

Reports a list containing only those items of list for which the boolean reporter is true -- in other words, the items satisfying the given condition.

In reporter, use ? to refer to the current item of list.

show filter [? < 3] [1 3 2]
=> [1 2]
show filter [first ? != "t"] ["hi" "there" "everyone"]
=> ["hi" "everyone"]

See also map, reduce, ?.

first

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

floor number

Reports the largest integer less than or equal to number.

show floor 4.5
=> 4
show floor -4.5
=> -5

follow

follow turtle

Similar to ride, but, in the 3D view, the observer's vantage point is behind and above turtle.

See also follow-me, ride, reset-perspective, watch, subject.

follow-me

follow-me

Asks the observer to follow the calling turtle.

See also follow.

foreach

foreach list [ commands ]
(foreach list1 ... [ commands ])

With a single list, runs commands for each item of list. In commands, use ? to refer to the current item of list.

foreach [1.1 2.2 2.6] [ show (word ? " -> " round ?) ]
=> 1.1 -> 1
=> 2.2 -> 2
=> 2.6 -> 3

With multiple lists, runs commands 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. In commands, use ?1 through ?n to refer to the current item of each list.

Some examples make this clearer:

(foreach [1 2 3] [2 4 6]
   [ show word "the sum is: " (?1 + ?2) ])
=> "the sum is: 3"
=> "the sum is: 6"
=> "the sum is: 9"
(foreach list (turtle 1) (turtle 2) [3 4]
  [ ask ?1 [ fd ?2 ] ])
;; turtle 1 moves forward 3 patches
;; turtle 2 moves forward 4 patches

See also map, ?.

forward
fd

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

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]

globals

globals [var1 ...]

This keyword, like the breed, <breeds>-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.

hatch
hatch-<breeds>

hatch number [ commands ]
hatch-<breeds> number [ commands ]

This turtle creates number new turtles. Each new turtle is identical to, and at the same location as, its parent. 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-<breeds> 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.

Note: While the commands are running, no other agents are allowed to run any code (as with the without-interruption command). This ensures that if ask-concurrent is being used, the new turtles cannot interact with any other agents until they are fully initialized.

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

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

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

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. Use set-plot-x-range to control the range of values to be histogrammed, and set the pen interval (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

home

The calling turtles moves to the origin (0,0). Equivalent to setxy 0 0.

hsb

hsb hue saturation brightness

Reports a RGB list when given a color in HSB format. Hue, saturation, and brightness are integers in the range 0-255. The RGB list contains three integers in the same range.

See also rgb

hubnet-broadcast

hubnet-broadcast tag-name value

This broadcasts value from NetLogo to the variable, in the case of Calculator HubNet, or interface element, in the case of Computer HubNet, with the name tag-name to the clients.

See the HubNet Authoring Guide for details and instructions.

hubnet-broadcast-view

hubnet-broadcast-view

This broadcasts the current state of the 2D view in the NetLogo model to all the Computer HubNet Clients. It does nothing for Calculator HubNet.

Note: This is an experimental primitive and its behavior may change in a future version.

See the HubNet Authoring Guide for details and instructions.

hubnet-enter-message?

hubnet-enter-message?

Reports true if a new computer 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?

hubnet-exit-message?

Reports true if a computer 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

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, hubnet-message-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-message

hubnet-message

Reports the message retrieved by hubnet-fetch-message.

See the HubNet Authoring Guide for details.

hubnet-message-source

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

hubnet-message-tag

Reports the tag that is associated with the data that was retrieved by hubnet-fetch-message. For Calculator HubNet, this will report one of the variable names set with the hubnet-set-client-interface primitive. For Computer HubNet, this will report one of the Display Names of the interface elements in the client interface.

See the HubNet Authoring Guide for details.

hubnet-message-waiting?

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

hubnet-reset

Starts up the HubNet system. HubNet must be started to use any of the other hubnet primitives with the exception of hubnet-set-client-interface.

See the HubNet Authoring Guide for details.

hubnet-send

hubnet-send string tag-name value

hubnet-send list-of-strings tag-name value

For Calculator HubNet, this primitive acts in exactly the same manner as hubnet-broadcast. (We plan to change this in a future version of NetLogo.)

For Computer HubNet, it acts as follows:

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-view

hubnet-send-view string

hubnet-send-view list-of-strings

For Calculator HubNet, does nothing.

For Computer HubNet, it acts as follows:

For a string, this sends the current state of the 2D view in the NetLogo model to the Computer HubNet Client with string for its user name.

For a list-of-strings, this sends the current state of the view in the NetLogo model to all the Computer HubNet Clients that have a user name that is in the list-of-strings.

Sending the 2D view to a nonexistent client, using hubnet-send-view, generates a hubnet-exit-message.

Note: This is an experimental primitive and its behavior may change in a future version.

See the HubNet Authoring Guide for details.

hubnet-set-client-interface

hubnet-set-client-interface client-type client-info

If client-type is "COMPUTER", client-info is an empty list for computer HubNet.

hubnet-set-client-interface "COMPUTER"[]

Future versions of HubNet will support other client types. Even for Computer HubNet, the meaning of the second input to this command may change.

See the HubNet Authoring Guide for details.

if

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

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.

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 [ifelse-value (?1 > ?2) [?1] [?2]]
  [1 3 2 5 3 8 3 2 1]
=> 8

See also if, ifelse.

import-drawing

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

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

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

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. Open the model from which you created the export file.
2. Press the Setup button, to get the model in a state from which it can be run.
3. Import the file.
4. Re-open any files that the model had opened with the file-open command.
5. 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

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 calling 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-<breed>-neighbor?
in-link-neighbor?

in-<breed>-neighbor? agent
in-link-neighbor? turtle

Reports true if there is a directed link going from turtle to the caller.

crt 2
ask turtle 0 [
  create-link-to turtle 1
  show in-link-neighbor? turtle 1  ;; prints false
  show out-link-neighbor? turtle 1 ;; prints true
]
ask turtle 1 [
  show in-link-neighbor? turtle 0  ;; prints true
  show out-link-neighbor? turtle 0 ;; prints false
]

in-<breed>-neighbors
in-link-neighbors

in-<breed>-neighbors
in-link-neighbors

Reports the agentset of all the turtles that have directed links coming from them to the caller.

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-<breed>-from
in-link-from

in-<breed>-from turtle
in-link-from turtle

Report the link from turtle to the caller. If no link exists then it reports nobody.

crt 2
ask turtle 0 [ create-link-to turtle 1 ]
ask turtle 1 [ show in-link-from turtle 0 ] ;; shows link 0 1
ask turtle 0 [ show in-link-from turtle 1 ] ;; shows nobody

__includes

__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

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 calling 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

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

int

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-boolean?
is-<breed>?
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?

is-agent? value
is-agentset? value
is-boolean? value
is-<breed>? 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-directed-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.)

;; suppose mylist is [2 4 6 8 10]
show item 2 mylist
=> 6
show item 3 "my-shoe"
=> "s"

jump

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?.

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

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

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 [[size] of ?1 < [size] of ?2] turtles 10

__layout-magspring

__layout-magspring turtle-set link-set spring-constant spring-length repulsion-constant magnetic-field-strength magnetic-field-type bidirectional?

Very similar to layout-spring, but with an added layer of complexity. The turtles in turtle-set attract and repel each other depending on the links (that are in link-set) between them, but there is also a magnetic field which the links try to align with.

The link-set is the set of links that exert forces on the turtles they are connected to. Turtles that are connected to links in the link agentset but are not included in the turtle agentset are treated as anchors. If there are no turtles with fixed positions the entire network will probably collapse on itself.

spring-constant is a measure of the "tautness" of the spring. (See layout-spring)

spring-length is the "zero-force" length or the natural length of the springs. (See layout-spring)

repulsion-constant is a measure of repulsion between the nodes. (See layout-spring)

magnetic-field-strength is the force of the magnetic field. (Reasonable values range from 0 to 1, but 0.05 is a good default.)

magnetic-field-type is a number in the range from 0 to 10. Choices are listed in the table below.

If bidirectional? is true then links try to align with the magnetic field by pushing attached turtles both in the direction of the field, and in the opposite direction. Otherwise, the links just push in a single direction.

to make-a-tree
  set-default-shape turtles "circle"
  crt 5
  ask turtle 0 [ 
    create-link-with turtle 1
    create-link-with turtle 2
  ]
  ask turtle 1 [
    create-link-with turtle 3
    create-link-with turtle 4
  ]
  ; layout with a fairly strong SOUTH magnetic field
  repeat 50 [ __layout-magspring 
              turtles with [who != 0] links 0.3 4 1 .50 5 false ] 
end

layout-radial

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

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 "circle"
  crt 3
  ask turtle 0
  [
    create-links-with other turtles
  ]
  ask turtle 1
  [
    create-link-with turtle 2
  ]
  repeat 30 [ layout-spring turtles links 0.2 5 1 ] ;; lays the nodes in a triangle
end

layout-tutte

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 "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
  ]  
  ; 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 [count link-neighbors = 1]) links 12 ]
end

left
lt

left number

The turtle turns left by number degrees. (If number is negative, it turns right.)

length

length list
length string

Reports the number of items in the given list, or the number of characters in the given string.

let

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

link end1 end2 <breed> 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

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

link-set

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

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

links

Reports the agentset consisting of all links.

show count links
;; prints the number of links

links-own
<link-breeds>-own

links-own [var1 ...]
<link-breeds>-own [var1 ...]

The links-own keyword, like the globals, breed, <breeds>-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 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]

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 

show log 64 2
=> 6

;; suppose mylist is [2 7 10 "Bob"]
set mylist lput 42 mylist
;; mylist now is [2 7 10 "Bob" 42]

M

show map [round ?] [1.1 2.2 2.7]
=> [1 2 3]
show map [? * ?] [1 2 3]
=> [1 4 9]

show (map [?1 + ?2] [1 2 3] [2 4 6])
=> [3 6 9]
show (map [?1 + ?2 = ?3] [1 2 3] [2 4 6] [3 5 9])
=> [true false true]

show max [xcor] of turtles
;; prints the x coordinate of the turtle which is
;; farthest right in the world

;; 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)

show max-one-of patches [count turtles-here]

;; prints the first patch with the most turtles on it

crt 100 [ setxy random-float max-pxcor
                random-float max-pycor ]
;; distributes 100 turtles randomly in the
;; first quadrant

show mean [xcor] of turtles
;; prints the average of all the turtles' x coordinates

show median [xcor] of turtles
;; prints the median of all the turtles' x coordinates

show member? 2 [1 2 3]
=> true
show member? 4 [1 2 3]
=> false
show member? "bat" "abate"
=> true
show member? turtle 0 turtles
=> true
show member? turtle 0 patches
=> false

show min [xcor] of turtles
;; prints the lowest x-coordinate of all the turtles

;; 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)

show min-one-of turtles [xcor + ycor]
;; reports the first turtle with the smallest sum of
;; coordinates

crt 100 [ setxy random-float min-pxcor
                random-float min-pycor ]
;; distributes 100 turtles randomly in the
;; third quadrant

number1 - (floor (number1 / number2)) * number2

show 62 mod 5
=> 2
show -8 mod 3
=> 1

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

;; to make the mouse "draw" in red:
if mouse-down?
  [ ask patch mouse-xcor mouse-ycor [ set pcolor red ] ]

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

;; make a 20-step movie of the current view
setup
movie-start "out.mov"
repeat 20 [
  movie-grab-view 
  go
]
movie-close

print movie-status
=> No movie.
movie-start
print movie-status
=> 0 frames; frame rate = 15.
movie-grab-view
print movie-status
1 frames; frame rate = 15; size = 315x315.

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

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
]

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
]

ask turtles
  [ ask patches in-radius 3
      [ set pcolor [color] of myself ] ]
;; each turtle makes a colored "splotch" around itself

N

ask n-of 50 patches [ set pcolor green ]
;; 50 randomly chosen patches turn green

show n-values 5 [1]
=> [1 1 1 1 1]
show n-values 5 [?]
=> [0 1 2 3 4]
show n-values 3 [turtle ?]
=> [(turtle 0) (turtle 1) (turtle 2)]
show n-values 5 [? * ?]
=> [0 1 4 9 16]

show sum [count turtles-here] of neighbors
  ;; prints the total number of turtles on the eight
  ;; patches around the calling 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

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

crt 2
ask turtle 0
[
  create-link-with turtle 1
  show link-neighbor? turtle 1  ;; prints true
]
ask turtle 1
[
  show link-neighbor? turtle 0     ;; prints true
]

netlogo-applet?

netlogo-applet?

Reports true if the model is running as an applet.

netlogo-version

netlogo-version

Reports a string containing the version number of the NetLogo you are running.

show netlogo-version
=> "4.0.5"

new-seed

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 NetLogo's allowed range of integers, -9007199254740992 to 9007199254740992.

new-seed never reports the same number twice in succession. (This is accomplished by waiting a millisecond if the seed for the current millisecond was already used.)

See also random-seed.

no-display

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 other one-of other turtles-here
if other != nobody
  [ ask other [ set color red ] ]

no-links

no-links

Reports an empty link agentset.

no-patches

no-patches

Reports an empty patch agentset.

not

not boolean

Reports true if boolean is false, otherwise reports false.

if not any? turtles [ crt 10 ]

no-turtles

no-turtles

Reports an empty turtles agentset.

of

[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 [who] of turtles
=> [0 1 2 3]
show sort [who * who] of turtles
=> [0 1 4 9]

one-of

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

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

Reports an agentset which is the same as the input agentset but omits the calling agent.

show count turtles-here
=> 10
show count other turtles-here
=> 9

other-end

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 turtle 0 [ create-link-with turtle 1 ]
ask turtle 0 [ ask link 0 1 [ show other-end ] ] ;; prints turtle 1
ask turtle 1 [ ask link 0 1 [ show other-end ] ] ;; prints turtle 0
ask link 0 1 [ 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-<breed>-neighbor?
out-link-neighbor?

out-<breed>-neighbor? turtle
out-link-neighbor? turtle

Reports true if there is a directed link going from the caller to turtle.

crt 2
ask turtle 0 [
  create-link-to turtle 1
  show in-link-neighbor? turtle 1  ;; prints false
  show out-link-neighbor? turtle 1 ;; prints true
]
ask turtle 1 [
  show in-link-neighbor? turtle 0  ;; prints true
  show out-link-neighbor? turtle 0 ;; prints false
]

out-<breed>-neighbors
out-link-neighbors

out-<breed>-neighbors
out-link-neighbors

Reports the agentset of all the turtles that have directed links from the caller.

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-<breed>-to
out-link-to

out-<breed>-to turtle
out-link-to turtle

Reports the link from the caller to turtle. If no link exists then it reports nobody.

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
]

output-print
output-show
output-type
output-write

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.)

patch

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 the calling 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

patch-ahead distance

Reports the single patch that is the given distance "ahead" of the calling 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 the calling 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

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 the calling 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

patch-at-heading-and-distance reports the single patch that is the given distance from the calling turtle or patch, along the given absolute heading. (In contrast to patch-left-and-ahead and patch-right-and-ahead, the calling 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 the calling patch
;;   green

See also patch, patch-at, patch-left-and-ahead, patch-right-and-ahead.

patch-here

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

patch-left-and-ahead angle distance
patch-right-and-ahead angle distance

Reports the single patch that is the given distance from the calling 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-and-distance instead.)

ask patch-right-and-ahead 30 1 [ set pcolor green ]
;; the calling 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

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.

patches

patches

Reports the agentset consisting of all patches.

patches-own

patches-own [var1 ...]

This keyword, like the globals, breed, <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, <breeds>-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

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

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

plot-name

Reports the name of the current plot (a string)

plot-pen-exists?

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

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

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 and mode are reset to the default values from the plot Edit dialog.

plotxy

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

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

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.

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

print

print value

Prints value in the Command Center, followed by a carriage return.

The calling 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.

random

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

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

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.

random-exponential reports an exponentially distributed random floating point number.

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

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

random-seed number

Sets the seed of the pseudo-random number generator to the integer part of number. The seed may be any integer in the range supported by NetLogo (-9007199254740992 to 9007199254740992).

See the Random Numbers section of the Programming Guide for more details.

random-seed 47823
show random 100
=> 57
show random 100
=> 91
random-seed 47823
show random 100
=> 57
show random 100
=> 91

random-xcor
random-ycor

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.

read-from-string

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

reduce [reporter] list

Reduces a list from left to right using reporter, resulting in a single value. This means, for example, that reduce [?1 + ?2] [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.

In reporter, use ?1 and ?2 to refer to the two objects being combined.

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] [1 2 3]
=> 6
show reduce [?1 - ?2] [1 2 3]
=> -4
show reduce [?2 - ?1] [1 2 3]
=> 2
show reduce [?1] [1 2 3]
=> 1
show reduce [?2] [1 2 3]
=> 3
show reduce [sentence ?1 ?2] [[1 2] [3 [4]] 5]
=> [1 2 3 [4] 5]
show reduce [fput ?2 ?1] (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
    [ifelse-value (length ?1 >= length ?2) [?1] [?2]]
    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
    [ifelse-value (?2 = x) [?1 + 1] [?1]] (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 [(x * ?1) + ?2] coefficients
end

;; evaluate 3x^2 + 2x + 1 at x = 4
show evaluate-polynomial [3 2 1] 4
=> 57

remainder

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

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

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

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 string2 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

repeat number [ commands ]

Runs commands number times.

     
 pd repeat 36 [ fd 1 rt 10 ]     
 ;; the turtle draws a circle    
 

replace-item

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

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

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

reset-ticks

Resets the tick counter to zero.

See also tick, ticks, tick-advance.

reset-timer

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.

reverse

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

rgb red green blue

Reports a RGB list when 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.

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.

See also reset-perspective, watch, follow, subject.

ride-me

ride-me

Asks the observer to ride the calling turtle.

See also ride.

right
rt

right number

The turtle turns right by number degrees. (If number is negative, it turns left.)

round

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

run

run string

This agent interprets the given string as a sequence of one or more NetLogo commands and runs them.

The code runs in the agent's current context, which means it has access to the values of local variables, "myself", and so on.

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 on different bits of code.

See also runresult.

Note that you can't use run to define or redefine procedures.

Note that running code through run or runresult may be many times slower than running the same code directly.

runresult

runresult string

This agent interprets the given string as a NetLogo reporter and runs it, reporting the result obtained.

The code runs in the agent's current context, which means it has access to the values of local variables, "myself", and so on.

The code must be compiled first which takes time, however, compiled bits of code are cached by NetLogo and thus using runresult on the same string over and over is much faster than running on different bits of code.

See also run.

Note that running code through run or runresult may be many times slower than running the same code directly.

scale-color

scale-color color number range1 range2

Reports a shade of color proportional to 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

self

Reports this turtle or patch.

"self" and "myself" are very different. "self" is simple; it means "me". "myself" means "the turtle or patch who asked me to do what I'm doing right now."

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

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

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 the calling agent
• If the calling 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.
• A special local variable (?, ?1, ?2...).

set-current-directory

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.

Note: in applets, this command has no effect, since applets are only allowed to read files from the same directory on the server where the model is stored.

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

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

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

set-default-shape turtles string
set-default-shape breed string

Specifies a default initial shape for all turtles, or for a particular breed. When a turtle is created, or it changes breeds, it shape is set to the given shape.

This command doesn't affect existing turtles, only turtles you create afterwards.

The specified breed must be either turtles or a breed defined by the breed keyword, and the specified 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 individual turtle's shape later; turtles 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

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-plot-pen-color

set-plot-pen-color number

Sets the color of the current plot pen to number.

set-plot-pen-interval

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

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).

set-plot-x-range
set-plot-y-range

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

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.

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?

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

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

show value

Prints value in the Command Center, preceded by the calling agent, and followed by a carriage return. (The calling 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

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.

See also hide-link.

shuffle

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

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

sort list-of-numbers
sort list-of-strings
sort agentset

If the input is a list of numbers or strings, reports a new list containing the same items as the input list, but in ascending order (numeric or alphabetic).

Any list items that are not numbers or strings are ignored. (If the input list contains no numbers or strings, the result is an empty list.)

If the input is an agentset or a list of agents, reports a list (never an agentset) of agents. If the agents are turtles, they are listed in ascending order by who number. If the agents are patches, they are listed left-to-right, top-to-bottom.

show sort [3 1 4 2]
=> [1 2 3 4]
let n 0
foreach sort patches [
  ask ? [
    set plabel n
    set n n + 1
  ]
]
;; patches are labeled with numbers in left-to-right,
;; top-to-bottom order

sort-by

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 (true or false) reporter.

In reporter, use ?1 and ?2 to refer to the two objects being compared. reporter should be true if ?1 comes strictly before ?2 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.

The sort is stable, that is, the order of items considered equal by the reporter is not disturbed.

show sort-by [?1 < ?2] [3 1 4 2]
=> [1 2 3 4]
show sort-by [?1 > ?2] [3 1 4 2]
=> [4 3 2 1]
show sort-by [length ?1 < length ?2] ["Grumpy" "Doc" "Happy"]
=> ["Doc" "Happy" "Grumpy"]
foreach sort-by [[size] of ?1 < [size] of ?2] turtles
  [ ask ? [ do-something ] ]
;; turtles run "do-something" one at a time, in
;; ascending order by size

sprout
sprout-<breeds>

sprout number [ commands ]
sprout-<breeds> 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-<breeds> 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 ]

Note: While the commands are running, no other agents are allowed to run any code (as with the without-interruption command). This ensures that if ask-concurrent is being used, the new turtles cannot interact with any other agents until they are fully initialized.

See also create-turtles, hatch.

sqrt

sqrt number

Reports the square root of number.

stamp

stamp

The calling 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

stamp-erase

The calling 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

Reports the unbiased statistical standard deviation of a list of numbers. Ignores other types of items.

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.

to startup
  setup
end

stop

stop

The calling agent exits immediately from the enclosing procedure, ask, or ask-like construct (crt, hatch, sprout, without-interruption). Only the current procedure stops, not all execution for the agent.

if not any? turtles [ stop ]
;; exits if there are no more turtles

Note: stop can be used to stop a forever button. 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.)

subject

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"

subtract-headings

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 80 60
=> 20
show subtract-headings 60 80
=> -20
show subtract-headings 5 355
=> 10
show subtract-headings 355 5
=> -10
show subtract-headings 180 0
=> 180
show subtract-headings 0 180
=> 180

sum

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

tan

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

tick

Advances the tick counter by one.

See also ticks, tick-advance, reset-ticks.

tick-advance

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.

See also tick, ticks, reset-ticks.

ticks

ticks

Reports the current value of the tick counter. The result is always a number and never negative.

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.

tie

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

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

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

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

turtle number <breed> 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

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

turtles-at
<breeds>-at

turtles-at dx dy
<breeds>-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
<breed>-here

turtles-here
<breeds>-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
<breeds>-on

turtles-on agent
turtles-on agentset
<breeds>-on agent
<breeds>-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
<breeds>-own

turtles-own [var1 ...]
<breeds>-own [var1 ...]

The turtles-own keyword, like the globals, breed, <breeds>-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 breed may list the same variable.)

breed [cats cat ]
breed [dogs dog]
breed [hamsters hamster]
turtles-own [eyes legs]   ;; applies to all breeds
cats-own [fur kittens]
hamsters-own [fur cage]
dogs-own [hair puppies]

See also globals, patches-own, breed, <breeds>-own.

type

type value

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.

The calling 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.

undirected-link-breed

undirected-link-breed [<link-breeds> <link-breed>]

This keyword, like the globals and breeds keywords, can only be used at the beginning of the Procedures 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

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.

uphill
uphill4

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]  ;; or neighbors4
if [patch-variable] of p > patch-variable [
  face p
  move-to p
]

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 uphill, uphill4.

user-directory

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

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

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 the reporter itself doesn't cause the file to be replaced. To do that you would use file-delete.

user-input

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?"

user-message

user-message value

Opens a dialog with value displayed as the message.

value may be of any type, but is typically a string.

user-message (word "There are " count turtles " turtles.")

user-one-of

user-one-of value list-of-choices

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 ]

user-yes-or-no?

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 ]

variance

variance list

Reports the sample variance of a list of numbers. Ignores other types of items.

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

wait

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 ]

See also every.

watch

watch agent

Puts a spotlight on agent. In the 3D view the observer will also turn to face the subject.

See also follow, subject, reset-perspective, watch-me.

watch-me

watch-me

Asks the observer to watch the calling agent.

See also watch.

while

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.

with

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

<breed>-with
link-with

<breed>-with turtle
link-with turtle

Report the link between turtle and the caller. If no link exists then it reports nobody.

crt 2
ask turtle 0 [
  create-link-with turtle 1
  show link-with turtle 1 ;; prints link 0 1
]

with-max

agentset with-max [reporter]

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

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

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 without-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

without-interruption [ commands ]

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. In previous versions of NetLogo, this command was often needed, but in NetLogo 4.0, it is only ever needed if you are also using 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"

world-width
world-height

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

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

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).

The calling agent is not printed before the value, unlike show. Its output will 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.

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

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

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,

?, ?1, ?2, ?3, ...

?, ?1, ?2, ?3, ...

These are special local variables. They hold the current inputs to a reporter or command block for certain primitives (for example, the current item of a list being visited by foreach or map).

? is always equivalent to ?1.

You may not set these variables, and you may not use them except with certain primitives, currently foreach, map, reduce, filter, sort-by, and n-values. See those entries for example usage.