transitioning to netlogo - wilkes universitymathcs.wilkes.edu/~rpryor/cs321/netlogo101.pdf · ﬁnd...

Transitioningto

NetLogo

Assignment:let x 5 ; Creates a new local variable and

; gives it the given value.

; If you want to change the value afterwards,

; use set. set x 5

Control:if x <=5 [ do this ]ifelse x <=5 [ do this ][ else ...do this ]

Iteration:repeat 10[ do this ]while [x <=5] [ do this ]

Procedure:to HelloThere [s]

; print se "Hello there, " stype "Hello there, "print s

end

observer> hellothere "Ron"Hello there, Ron

Functions:to-report avg [x y]

report (x + y) / 2end

observer> print avg 7 87.5

I/O:

print show type write

Random Numbers:

random random-float random-exponentialrandom-normal random-poisson random-gamma

Statistics:

histogram max min mean medianmodes standard-deviation variance

List Processing:

first last butfirst butlast removeitem length sumsort shuffle reversesentence word listrun

Files:

file-open file-closefile-read file-read-line file-read-charactersfile-print file-show file-type file-print

to tryMe [n] let c 0

let comma ”,”file-open "/Users/rpryor/Desktop/my-file-out.csv"

while [c < n] [file-write (random-normal 3 1) file-type comma set c c + 1]

file-type random-normal 3 1 file-close

end

NetLogo

ProgrammingAN INTRODUCTION

Author: Alan G. Isaac

Organization: American University

NetLogo Basics

BACKGROUND

PRELIMINARIES

First read the NetLogo Basics

GOALS

After mastering this section, you will be able to:

use NetLogo’s branching and looping constructs

create procedures and reporters

NetLogo Programming https://subversion.american.edu/aisaac/notes/netlogo-intro.xhtml

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find NetLogo “Code examples” to simplify your own programming task

modify an existing NetLogo model

build a new NetLogo model

CODE EXAMPLES

The NetLogo Models Library includes a collection of code examples. Be sure to look at

these for hints whenever you get stuck.

PROGRAM STRUCTURE

THE CCOODDEE TAB: GLOBAL VARIABLES

comments:

a semicolon (;;) begins a comment for remainder of line

global variables

each global variable must be declared in the declarations section

every agent can access a global variable. (Roughly, they belong to the

observer.)

values are assigned (or reassigned) with the sseett command

THE CCOODDEE TAB: DECLARATIONS AND PROCEDURES

declarations section

gglloobbaallss [[......]]

declares a list of global variables

other global variables declared in sliders

may be thought of as oobbsseerrvveerr--oowwnnss

ttuurrttlleess--oowwnn [[......]], ppaattcchheess--oowwnn [[......]],

lliinnkkss--oowwnn [[......]]

declare a list of instance attributes for each agent type

procedures section (only contains procedures and reporters)

ttoo mmyy--pprroocceedduurree ...... eenndd

ttoo--rreeppoorrtt mmyy--rreeppoorrtteerr ...... eenndd

a procedure that returns a value is called a “reporter”

reporters must use rreeppoorrtt

KEYWORDS


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In the Code tab, outside of code blocks, we should only find:

comments

NetLogo keywords

<<iinnssttaanncceess>>--oowwnn (see below)

Comment: many of the NetLogo documentation examples are slightly misleading on this

score. E.g., http://ccl.northwestern.edu/netlogo/docs/dictionary.html#breed

KEYWORDS

http://ccl.northwestern.edu/netlogo/docs/dictionary.html#Keywords

extensions http://ccl.northwestern.edu/netlogo/docs/extensions.html

__includes http://ccl.northwestern.edu/netlogo

/docs/dictionary.html#includes

globals

breed, directed-link-breed, undirected-link-breed

patches-own, turtles-own, <breeds>-own, links-own, <link-breeds>-own

to, to-report, end

EXTENSIONS

See: Help > NetLogoUser Manual > Extensions

standard extensions

array, table, GoGo, Profiler, GIS, Sample, and Sound are in the standard

installation

sound (MIDI sounds and sound file playback)

located in Extensions subfolder of NetLogo installation folder

Some (GIS, Table) come with existing models

NetLogo 3D

NetLogo can locate agents in 3d spaces

patches becomes cubes

see examples in Models Library

other important extensions

R extension: http://netlogo-r-ext.berlios.de/

MORE EXTENSIONS (3RD PARTY)

There are many third-party extensions for NetLogo. Here are a couple of examples:

graphics extension http://evolve.lse.ac.uk/NetLogo/extensions/Simulations-

NetLogo%20Extensions.php

shell extension https://github.com/NetLogo/Shell-Extension/


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BASIC PROGRAM STRUCTURE

Even the simplest NetLogo programs traditionally include the following structure:

globals

declaration of global variables using the gglloobbaallss keyword

setup

a procedure named sseettuupp that initializes the global varaibles and does other

setup operations

go

a procedure that runs one iteration of the model; this holds the “schedule” for your

program

EXAMPLE: MINIMAL PROGRAM STRUCTURE

globals [ gvar01 gvar02 ]

to setup

clear-all

end

to go

do-stuff

end

to do-stuff

...

end

APPLICATION: MINIMAL PROGRAM STRUCTURE

globals [ n-heads n-tails ]

to setup

clear-all

end

to go

repeat 50 [ flip-coin ]

end

to flip-coin

;; fill in procedure body

end

PARAMETERS FOR PROCEDURES


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Procedures and reporters can specifiy formal parmeters in brackets after the name. As a

convention, we will begin formal parameter names with a hash mark. (These names are

strictly local to the procedure.)

to-report is-equal? [#x #y]

ifelse #x = #y [report true] [report false]

end

See: http://ccl.northwestern.edu/netlogo/2.0/docs/programming.html#procedures2

PLOTTING: FIRST STEPS

PLOTTING

Plots are added through the GUI. (In your program you can refer to them by the name you

give them at creation.)

http://ccl.northwestern.edu/netlogo/docs/programming.html#plotting

In the NetLogo Models Library, under Code Examples, see PPlloottttiinngg EExxaammppllee.

BASIC CONCEPTS: PLOTS

You can add plots to the IInntteerrffaaccee window. Just right click where you want it

located, and fill in the resulting dialogue.

For the moment, we will only change the ppeenn uuppddaattee ccoommmmaannddss.

pen update commands

commands to be executed when the plot updates

update-plots

NetLogo primitive that we will call in our ggoo procedure

EXERCISE: BASIC PLOT

In the CCooddee window, create a coin-flipping program that has the following ggoo

procedure:

to go

set n-heads 0

repeat 50 [ flip-coin ]

update-plots


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end

Add a plot with the pen update command pplloott nn--hheeaaddss.

In the Command Center, run your sseettuupp procedure, and then run your ggoo procedure

100 times.

EEXXPPOORRTT--PPLLOOTT

export-plot writes a comma-separated values file. There data written includes the x and y

values of all points plotted by all the plot pens in the plot.

Specify the plotname as a string: it is the same as whatever you entered as the name in the

plot dialogue (which is used as the title of your plot).

The data is written to an external file. You specify the filename as a string. Use forward

slashes.

See: http://ccl.northwestern.edu/netlogo/docs/dictionary.html#export-plot

PLOT COMMANDS

most-used plot commands:

histogram, plot, plotxy, set-current-plot, set-current-plot-pen, set-plot-pen-mode

often-used plot commands:

set-histogram-num-bars set-plot-pen-color set-plot-x-range set-plot-y-range

autoplot (automatic axes range adjustemnts):

autoplot? auto-plot-off auto-plot-on

clear-plot related commands:

clear-all-plots clear-plot plot-pen-reset

other plot commands:

http://ccl.northwestern.edu/netlogo/docs/dictionary.html#plottinggroup

SIMPLE HISTOGRAM

Suppose we have turtles classified by color: red, green, or blue. After using the GUI to

create a plot titled "Class Histogram", we can:

to update-class-histogram

set-current-plot "Class Histogram"

histogram map [position ? [red green blue]] ([color] of turtles)

end


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CUSTOM HISTOGRAM

If we would like to color-code our bars, we cannot use hhiissttooggrraamm. Instead we plot a

bar for each value.

to update-class-histogram

set-current-plot "Class Histogram"

plot-pen-reset

set plot-pen-mode 1 ;; bar mode

set-plot-pen-color red

plot count turtles with [color = red]

set-plot-pen-color green

plot count turtles with [color = green]

set-plot-pen-color blue

plot count turtles with [color = blue]

end

PLOTTING GINI COEFFICIENT AND LORENZ CURVE

let cumsum-sorted-wealths

partial-sums sort [wealth] of turtles

let total-wealth last cumsum-sorted-wealths

let normalized-wealths

map [? / total-wealth] cumsum-sorted-wealths


...

let n length normalized-wealths

let gaps n-values n

[((? + 1) / n) - item ? normalized-wealths]

set gini (2 * sum gaps / n) ;; Gini = A/(A+B) = 2*A

set-current-plot "Gini Dynamics" plot gini


...

set-current-plot "Dynamic Lorenz Curve"

set-current-plot-pen "lorenz01a" plot-pen-reset

set-plot-pen-interval 1 / n

plot 0


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foreach normalized-wealths [plot ?]

Building NetLogo Models

FIRST STEPS

STEPS TOWARD MAKING YOUR OWN MODELS

Experiment with existing models via GUI

Models Library downloads with installation (File > Models Library)

http://ccl.northwestern.edu/netlogo/models/

other publicly available models on the web http://www.openabm.org/

1.

Modify existing models2.

Roll your own3.

MODIFYING MODELS

find a model that does something close to what you want

save it under a new name

modify it to suit your needs

update the model information to match your changes

make sure to appropriately attribute all code (i.e., honor the copyrights)

structured and commented code

– helpful to others who read your code – helpful to you in both writing and

understanding your code

SIMPLE MODIFICATIONS

You might want to change the World settings

size


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location of 0, 0

torus or rectangle

patch size (this and size determine size of world screen)

MODEL DECISIONS

system to be modeled

what do the agents represent?

what are the rules of action and interaction?

how will you approximate these rules for entry into the modeling environment?

what does a tick (cycle) represent?

SIMPLE MODEL

A basic model will have:

sseettuupp procedure1.

ggoo procedure2.

For example:

sseettuupp procedure

create turtles (ccrrtt or sspprroouutt)

random headings? (the default)

random positions? (origin is the default)

ggoo procedure

move the turtles with random distance and headings

randomly change speed (jump size) and headings

SIMPLE MODEL ...

A basic model may have:

ssttaarrttuupp procedure

If you name a procedue ssttaarrttuupp, it will be run when your model first

loads.

sliders

sliders let users control model parameters, e.g., the speed range and the

angle range for heading changes

easy to add in NetLogo GUI

graphs

graphs can dynamically monitor a single value (plot), pairs of values

(plotxy), or collections of values (histogram)

easy to add in NetLogo GUI


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NetLogo Programming

Language

PROGRAMMING IN NETLOGO

CONTEXT IN NETLOGO

context: who is acting

the default actor/agent is the observer, but ...

aasskk ttuurrttlleess sets context to turtles

aasskk ttuurrttllee 00 sets context to turtle 0

agents can ask other agents to do things

aasskk ttuurrttlleess [[ aasskk lliinnkkss [[ …… ]]…… ]]

only the agent that “owns” an attribute can find the value or change the value

BREEDS

new breeds can be declared in the declarations section of a script:

breed [ thieves thief ]

a breed is like a “subtype” of turtle: it has all the attributes of turtle, plus any new

attributes declared for the breed. E.g.,

thieves-own [ skill known? ]

Turtles and links come with a bbrreeeedd attribute, which can be reset.

show [ breed ] of turtle 0

ask turtle 0 [ set breed thieves ]


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LINKS

create-link-with

create an undirected link between the caller and agent

create-link-to

create a directed link from the caller to agent

create-link-from

creates a directed link from agent to the caller

LINK BREEDS

Link breeds must be declared as either directed or undirected. These breeds may own

variables. (See the Link Breeds Example in the Model Library.)

directed-link-breed [unis uni]

undirected-link-breed [bis bi]

bis-own [weight]

...

ask turtule 0 [create-uni-to turtle 1]

ask turtule 0 [create-bis-with other turtles]

LANGUAGE BASICS

LANGUAGE BASICS

reassignment: set a b

use parentheses to control order of operations

use brackets [[ ]] for code blocks

white space ignored after initial space

procedures and reporters (see above)

BASIC DATA TYPES

numbers

all numbers are floating point

lists

immutable


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System Message: WARNING/2 (nneettllooggoo--iinnttrroo..rrsstt, line 583)

Definition list ends without a blank line; unexpected unindent.

strings

booleans (true or false)

AGENTSETS

turtlesets

patchsets

linksets

EXTENSION DATA TYPES

tables

arrays

LANGUAGE SURPRISES

use ((-- nnuummbbeerrnnaammee)), not --nnuummbbeerrnnaammee

case-insensitive

necessary white space: set a (3 * b)

RECENT CHANGES

see the Transition Guide: http://ccl.northwestern.edu/netlogo

/docs/transition.html

rreesseett--ttiicckkss: as of version 5, you must explicitly call rreesseett--ttiicckkss

to initialize the ticks counter; it is no longer called by cclleeaarr--aallll

NetLogo 5: can no longer concatenate strings with ++; use wwoorrdd

rraannddoomm--oonnee--ooff was renamed oonnee--ooff

LANGUAGE CONVENTIONS

Logical variables end in ??

procedure body indented


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two semicolons to start comment ;;;;

TICKS

NetLogo includes a built-in tick counter:

print ticks ;; display current value of ticks

tick ;; increment ticks (by 1)


reset-ticks ;; reset ticks to 0


CONTROL FLOW: BRANCHING

http://ccl.northwestern.edu/netlogo/docs/dictionary.html#controlgroup

if (condition) [commands]

ifelse (condition) [commands4true] [commands4false]

ifelse-value (condition) [reporter4true] [reporter4false]

BOOLEANS AND CONDITIONAL BRANCHING

NetLogo has boolean primitives, ttrruuee and ffaallssee. Comparisons (e.g., >> or <<)

produce a boolean result, which can be used for conditional code execution. E.g., noting

that rraannddoomm--ffllooaatt 11 is between zero and one:

if (random-float 1 < 0.5) [show "heads"]

We might also like the observer to print “tails” for larger outcomes. We can use the

iiffeellssee construct to do this.:

ifelse (random-float 1 < 0.5)

[show "heads"]

[show "tails"]

Note that to create a string, we bracket a sequence of characters with double quotes.

IIFFEELLSSEE--VVAALLUUEE

NetLogo also provides the unusual iiffeellssee--vvaalluuee primitive, which allows

condition determination of a value.


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ask turtles [

set color ifelse-value (wealth < 0) [red] [blue]

]

http://ccl.northwestern.edu/netlogo/docs/dictionary.html#ifelse

CONTROL FLOW: LOOPING

foreach list [commands]

repeat

stop

while

loop (forever!)

other: ask ask-concurrent carefully error-message every run runresult to

to-report wait with-local-randomness without-interruption

OPERATORS: MATH, LOGIC AND COMPARISON

math

+, -, /, ^

white space delimited (e.g., 33 ++ 22 not 33++22)

all are binary, but can write ((-- xx)) for 00 -- xx

logical operators (operate on booleans)

and, not, or, xor

comparison (http://ccl.northwestern.edu/netlogo/docs/dictionary.html#Symbols)

>, >=, <, <=, =, !=

GLOBAL VARIABLES

have global scope (i.e., are available anywhere in the program)

must be declared before used

in the declarations section, or

by adding a button

use sseett aa bb to change the value of variable aa

LOCAL VARIABLES

lleett aa bb declares a new local variable aa and assigns it the value of bb

scope restricted to code block in which declared

cannot be declared with global scope

sseett aa bb changes the value of aa to the value of bb


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LISTS

AGENTSETS VS. LISTS

agentset

an unordered collection of agents

traverse with aasskk

aasskk aaggeennttsseett [[ lliisstt ooff ccoommmmaannddss ]]

list

an ordered, immutable collection of objects

traverse the list items sequentially with ffoorreeaacchh

?? is special name for current list item in the ffoorreeaacchh sequence

E.g., ffoorreeaacchh [[11..11 22..22 22..66]] [[ pprriinntt rroouunndd ?? ]]

will print 1, 2, 3.

CREATING LISTS

list constants between brackets:

lleett mmyylliisstt [[00 11 22 33]]

use lliisstt to make a list from variables:

lleett aa 00 lleett bb 11 lleett mmyylliisstt ((lliisstt aa bb))

use the sseenntteennccee primitive (to append to or concatenate):

sseenntteennccee [[00 11]] 22

sseenntteennccee [[00 11]] [[22 33]]

use ooff with an agentset:

[[ccoolloorr]] ooff ttuurrttlleess

OPERATING ON LISTS

http://ccl.northwestern.edu/netlogo/docs/dictionary.html#listsgroup

sublists

sublist, remove-duplicates

remove item list, remove-item int list

but-first, but-last

new lists


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replace-item int list

fput, lput, sentence

n-of int list, n-values int [reporter]

reverse, shuffle

sort, sort-by

membership

member?

IMMUTABILITY

NetLogo lists are immutable: you construct new lists based on old lists.

if you want an extant variable to refer to a new list, use sseett.

set mylist replace-item 0 mylist 99

; mylist's first element is now 99

set mylist lput 100 mylist

; appends the value 100 to mylst

set mylist fput -1 mylist

; mylist now has a new first element

OPERATING ON LISTS ...

zero based indexing:

iitteemm 00 [[00 11 22]]

list items

first mylst, last mylst, item int mylst, one-of list

member? value list, position item list

other

empty?, length

INTRODUCTION TO FUNCTIONAL PROGRAMMING

mmaapp

apply a reporter to a list and produce a new list.

The current item is represented by ??.

E.g., mmaapp [[?? ** ??]] [[00 11 22]] reports [[00 11 44]].

ffiilltteerr

report a new list with only some of the members of the given list:

E.g., ffiilltteerr [[?? << 22]] [[11 22 11 22]] reports [[11 11]].

rreedduuccee

combine the items of a list into a single result:


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E.g., rreedduuccee [[??11 ++ ??22]] [[11 22 33]] reports 66.

ssoorrtt--bbyy

sort a list based on a comparions.

E.g., ssoorrtt--bbyy [[??11 >> ??22]] [[33 11 44 22]] reports [[44 33 22 11]]

FFOORREEAACCHH

run commands for each item of a list

syntax: ffoorreeaacchh **lliisstt** [[**ccoommmmaannddss**]]

simple example:

let range n-values 10 [?]

foreach range [show ? * ?]

or equivalently:

foreach n-values 10 [?] [show ? * ?]

FFOORREEAACCHH WITH MULTIPLE LISTS

The ffoorreeaacchh command can be used with multiple lists of identical length. The first

result is computed from the first elements of the arguments. The second result is computed

from the second elements of the arguments. For example:

(foreach [1 2] [3 4] [5 6] [print ?1 + ?2 + ?3])

Note the required parentheses.

NESTED FFOORREEAACCHH

to-report moore-offsets [radius]

let dxdy (list ) ;; empty list

let offsets n-values (2 * radius + 1) [? - radius]

foreach offsets [

let xoff ?

foreach offsets [

let yoff ?

set dxdy lput (list xoff yoff) dxdy

]

]


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report dxdy

end

RREEDDUUCCEE

reduce [reporter] list

reduce a list from left to right using reporter, resulting in a single value.

use ?1 and ?2 in your reporter to refer to the two objects being

combined.

example: reduce [?1 + ?2] [1 2 3]

→ 6

CUMULATIVE SUM VIA RREEDDUUCCEE

Written by Seth Tisue

to-report partial-sums [nums]

let total 0

let result []

foreach nums [

set total total + ?

set result lput total result

]

report result

end

CUMULATIVE SUM VIA RREEDDUUCCEE (V.2)

to-report partial-sums [lst] ;; written by Seth Tisue

report butfirst reduce [lput (?2 + last ?1) ?1] fput [0] lst

end

OUTPUT

BEHAVIORSPACE

parameter sweep

systematic variation of scenarios

standard method for exploring the parameter space


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BehaviorSpace

a NetLogo tool for easily implementing a parameter sweep

USING BEHAVIORSPACE

Tools > Behavior Space > New

give your experiment a name

specify multiple values of parameters for your experiment

list the values explicitly, or use a range [[ssttaarrtt iinnccrreemmeenntt

eenndd]]

[[""mmyyppaarraamm"" 00 11 22 33]], or [[""mmyyppaarraamm"" [[00 11 33]]]]

you can vary the world size! (not a parameter in an ordinary sense)

fill in the experiment information

click “ok” when you are done

save your NetLogo model (this will save your experiment settings)

run the experiment by pressing the RRuunn button

you will be prompted for how to save your data before the experiment

runs

it runs much more quickly if you uncheck “update graphics” and “update

plots and monitors”.

BEHAVIOR SPACE ...

Repetitions

the number of repetitions for each parameter combination

reporters

one per line, for each variable you want to record

Setup commands:

usually just your sseettuupp procedure

Go commands:

the procedure that runs one step of your model, usually named ggoo

Stop condition:

a reporter that reports ttrruuee when the run should stop (or just set the number of

iterations as a TTiimmee LLiimmiitt)

OPEN A FILE

Unlike many languages, NetLogo does not allow you to specify upon opening whether

you will read from or write to the file. That is determined by the next file primitive you

use (e.g., ffiillee--rreeaadd or ffiillee--wwrriittee).

If you open an existing file and write to it, you will append to that file. If you want to

replace the content of an existing file, you will have start with a ffiillee--ddeelleettee.


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Once you are done with an open file, you should close it with ffiillee--cclloossee.

OPEN A FILE FOR WRITING

In order to open a file for writing and close it afterwards, you need the following

commands:

ffiillee--ddeelleettee string

delete the file designated by string

ffiillee--ooppeenn string

open a file for reading or appending (but not both)

ffiillee--cclloossee:

close an open file

USING CCAARREEFFUULLLLYY WITH FFIILLEE--DDEELLEETTEE

If you want to replace the content of a file, say tteemmpp..ttxxtt, you should begin by

deleting the existing file. But suppose you do not know ahead of time whether the file

exists: deleting a file that does not exist is a runtime error. To work around this issue, use

ccaarreeffuullllyy. http://ccl.northwestern.edu/netlogo/docs/dictionary.html#carefully

carefully [file-delete "c:/temp/temp.txt"] []

file-open "c:/temp/temp.txt"

file-print "test 01"

file-close

FILE OUTPUT

In order to write information to external files, you may find the following commands to be

useful.

ffiillee--pprriinntt value

write value to open file, followed by carriage return

ffiillee--sshhooww value

first write the agent to file, then write value to open file, followed by carriage

return

ffiillee--ttyyppee value

write value to open file, not followed by carriage return (strings are written

without quotes; backslashes escape control characters)

ffiillee--wwrriittee value

write a space and then write value to open file, not followed by carriage return

(strings are written quote delimited; backslahses are literal)


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EXAMPLE

Try this in the command center:

file-delete "c:/temp/temp.txt"


file-print "Minimum mean maximum"

file-type 10 file-write 15 file-write 20

file-print ""

file-close

Note use forward slashes in your paths.

FILE-BASED INPUT

In order to read external information into your program, you may find the following

commands to be useful.

ffiillee--ooppeenn string:

open a file for reading or appending (but not both)

ffiillee--cclloossee:

close an open file

ffiillee--rreeaadd--lliinnee:

read the next line and return it as a string (without terminators)

ffiillee--rreeaadd:

read the next "constant" (e.g., number, list, or string) and return it

ffiillee--aatt--eenndd??:

report true if last character of file has been read

EXAMPLE

Try this in the command center:


print file-read-line

file-close

Note use forward slashes in your paths.

EXAMPLE: FILE-BASED INPUT

Suppose the nnllddaattaa0011..ttxxtt looks like:


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pxcor pycor n-turtles

0 0 5

1 0 3

You could handle this as follows:

file-open "nldata01.txt"

let trash file-read-line ;; discard header line

while [not file-at-end?] [

ask patch file-read file-read [sprout file-read]

]

file-close

EXAMPLE: FILE-BASED INPUT (PYTHON)

fin = open('nldata01.txt', 'r')

trash = next(fin)

data = dict()

for line in fin:

x, y, n = map(int, line.split())

data[(x,y)] = n

fin.close()

BEHAVIORSPACE AND FILE OUTPUT

If you want to make your own output files during BehaviorSpace runs, use the

bbeehhaavviioorrssppaaccee--rruunn--nnuummbbeerr primitive. Alternatively, produce filenames

based on parameter values.

["globalA" 1 2 3]

["gloablB" 4 5 6]

file-open (word "myfile-" globalA "-" globalB ".txt")

Of course you can combine these two approaches.

If you needs even more flexibility, consider Charles Staelin's ppaatthhddiirr extension. It

might still be here: http://sophia.smith.edu/~cstaelin/NetLogo/pathdir.html

NetLogo Resources


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MANUAL

USER MANUAL

http://ccl.northwestern.edu/netlogo/docs/ includes tutorials and the following:

Interface Guide

Programming Guid

NetLogo Dictionary

GUIDES

Interface Guide

http://ccl.northwestern.edu/netlogo/docs/interface.html

world settings: size, topology (wrapping vs. reflecting)

menu items, controls

Programming Guide

http://ccl.northwestern.edu/netlogo/docs/programming.html

NetLogo Dictionary

http://ccl.northwestern.edu/netlogo/docs/dictionary.html

alphabetical list

also grouped by type

DOWNLOAD, INSTALL, AND RUN (WINDOWS

VERSION)

Download

Go to: http://ccl.northwestern.edu/netlogo/

Download link on the left

Save to desktop or accept the default

Install

Double-click on downloaded file to install (NetLogo4.1Installer.exe)

Accept all defaults

Run (Windows version)

Start > All Programs > NetLogo > NetLogo 4.1

PUTTING NETLOGO MODELS ON THE WEB

http://ccl.northwestern.edu/netlogo/docs/applet.html


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SaveAs > Applet

Java Virtual Machine (JVM) included (solves problems: old versions

work!)

applet can read and write files on your computer, but not on your users’

computers

OTHER NETLOGO RESOURCES

discussion group: http://groups.yahoo.com/group/netlogo-users/

homepage includes mail lists, documentation, and example models

http://ccl.northwestern.edu/netlogo/

onlines articles and papers, e.g.,

http://ccl.northwestern.edu/papers/

http://ccl.northwestern.edu/papers/netlogo-outside.html

MODELS LIBRARY: LIFE

MODELS LIBRARY: LIFE

Models Library

Computer Science > Cellular Automata > Life

use of patches to implement cellular automaton

just patches (cells); no turtles

cells have two states: alive and dead

Dark = cell alive, background color = dead

Transition rule

dead cell with 3 or more live neighbors comes to life

live cell with 2 live neighbors continues to live

live cell with less than 2 live neighbors dies

MODELS LIBRARY: HEAT BUGS

FFiillee >> MMooddeellss LLiibbrraarryy >> BBiioollooggyy >> HHeeaattbbuuggss

famous biological model

each bug radiates a little heat

bugs move if they are too hot or cold

Compare to the 'Collectivities' model.


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MODELS LIBRARY: PARTY

Models Library

Social Science > Party (famous in another form)

implements the Schelling segregation model

two types of people (e.g., men and women)

otherwise the same attributes

Key parameter:

how “comfortable” are these agents being in a local minoriy

adjustable parameter (slider)

Discovery

Even a slight preference can lead to complete segregation

MODELS LIBRARY: SMALL WORLD

Models Library > Networks > Small Worlds

famous: six degrees of separation

new tools

uses links

path along links from one agent to another

Setup

initalize links in a ring (each agent links to an agent each side)

key outcome concerns the average path length for all pairs of agents

even a few random new links substantially reduces the average path

length

potentially significant for organizational design

potentially significant for disease transmission

MODELS LIBRARY: EL FAROL

Models Library > Social Science > ElFarol

another version: http://www.markgarofalo.com/ABS/ElFarol

/ElFarolBarProblem.html

Readings: [garofalo-2006-wp], [wilensky.rand-2007-jasss]

MODELS LIBRARY: PREDATION

File > Models Library > Biology > Wolf Sheep Predation

use of breeds (wolves, sheep)

more interesting variant: patches grow grass that sheep eat (click grass?

Switch to On)


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boom-and-bust cycles common (with sheep and wolves negatively

correlated)

MODELS ON NETLOGO SITE

URL: ccl.northwestern.edu/netlogo/ > Community

possible problems if models are written for earlier versions of NetLogo

MODELS ON NETLOGO SITE

Miller & Page Applause Model

http://luis.izqui.org/models/standingovation/

Readings: [miller.page-2004-complexity]

REFERENCES

Axtell, R., Axelrod, R., Epstien, J. M., and Cohen, M. D. (1996). Aligning simulation

models: A case study and results. Computational and Mathematical Organization Theory,

1:123–141.

Resnick, M. (1997). Turtles, Termites, and Traffic Jams: Explorations in Massively

Parallel Microworlds. MIT Press.

[garofalo-

2006-wp]

Garofalo, Mark. (2006) "Modeling the 'El Farol Bar Problem' in

NetLogo". Dexia Bank Belgium . http://ccl.northwestern.edu

/papers/netlogo-outside.html

[miller.page-

2004-complexity]

Miller, John H, and Scott E Page. 2004. The Standing

Ovation Problem. Complexity 9, 8--16.

[wilensky.rand-

2007-jasss]

Wilensky, Uri, and William Rand. 2007. Making Models Match:

Replicating an Agent-Based Model. Journal of Artificial

Societies and Social Simulation 10, Article 2.

http://jasss.soc.surrey.ac.uk/10/4/2.html

LEGALITIES

Copyright © 2012 Alan G. Isaac. Some rights reserved. This document is

licensed under a Creative Commons Attribution License.


26 of 26 7/20/12 4:14 PM

First Steps with NetLogoLets take a few first steps with our modeling frameworks. We will be fairly brief , limiting ourselves to simple "kicking thetires" and writing a hello world in each ABM system (here is the RePast First Steps). Our goal is to gain a feel for what eachsystem is capable of so that we can make intelligent decisions on which one to use for a given task. Note: most imagesbelow can be clicked on for a full size image.

Introducing NetLogo

To download NetLogo, go to their web site, downloading the package for your system. As of thiswriting, the version is 1.2. During the download you can join the mail list, which I recommend.

The package will include considerable browser-based documentation in the docs/ directory for fastviewing. I show the results of downloading "Other Java-enabled platform" to the right. TheNetLogo.jar is double clickable, starting the application. Specific downloads are available for Macand Windows.

The NetLogoLite.jar file is used for exporting your models to the web, like this example.

When NetLogo starts, you are presented with an empty model, left, whichyou can modify. You also can browse the Model Library, right. Start byselecting the Segregation model from the Social Science collection.

To run the model, click "Setup", then "go". The model runs until each agent(called turtles) is "satisfied" .. i.e. has neighbors of at least "%-similar-wanted" as himself. You can experiment with number of turtles and the %setting by changing the sliders.

Note the surprising result with the initial settings: wanting 30% similar neighbors generally results in over 70% similar! Thissuggests very minor desire for similarity among residents of a neighborhood results in segregation. Click on the tabs on thetop of the window to see more information about the model, and to see the source code itself. The code is surprisinglysimple for what it does.

Now lets try a few simple commands. To do this, we'll select New in the File menu to get an empty new model. Thispresents just two items: the graphics window and the command center. The graphics window shows the patches and turtles,while the command center lets you type in commands, helpful for experimenting to see how they work.

Kicking The Tires: The Command Center

The command center accepts commands in three contexts: commands for the global Observer, or for commands sent to all ofthe individual Turtles or Patches as a group. You choose which sort of command you want via the small drop down menu. In the image below left we show the patches being selected. The center image shows the result of one command: "setpcolor (pxcor + pycor)" which simply sets the color (a number between 0 and 140) to the sum of the x and ycoordinates. Note that, because the command is going to all of the patches, the entire Graphics Window is changed. Sillybut illustrative! We then switch to Observer mode and reset the display and create 36 turtles with these two commands:"clear-patches" and "create-turtles 36". We then switch to Turtle mode, and do "set heading who *10" and "forward 15" which turns the turtles in all directions ("who" is the number of the turtle from 0 to 35) and thenhas them move forward 15 units, resulting in the image on the right.

First Steps with NetLogo http://complexityworkshop.com/cw/tutorial/NetLogo/

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Programs are run using a very simple Logo-like language, along with an easy to use GUI forbuilding sliders, buttons, and graphs. To understand this a bit further, we'll use the (excellent!)documentation that came with the download. The index page is to the right. Use your browser tolook at the doc/index.html that came with your system.

Take some time to browse through the documentation. The three tutorial modules are quite good asare the three reference sections. Look at the Interface Guide .. it will show you all the visiblecomponents in a model, and explain how they are used. Then look at the Programming Guide .. itwill guide you through all of the NetLogo language features. Finally, the Primitives Dictionarygives detailed information on every language primitive. It will be your constant companion as youwrite models!

Buttons: A "Hello World" Model

In Stuart Kauffman's wonderful book "At Home in the Universe", he presents an exampleof a rapid "phase transition". This is modeled by a set of buttons which, during each turn,a random pair are chosen to be tied together.

Initially there are lots of isolated pairs tied together. Later threes, fours and abruptly thereis a steep transition to most of the buttons being tied together .. an emergent giant cluster. In the example shown here, there are 500 buttons and we plot 1000 turns. The rapidchange occurs at around the 1/4 mark where the number of threads is about half thenumber of buttons.

We can model this in NetLogo by having the buttons be turtles placed randomly on the graphicwindow. Each tick we will chose a pair of buttons, connecting them together and changingtheir color to be the same. At the end of each turn we will find the largest cluster, posting itssize.

Before we start, you can try the model in your browser, and browse the source code.

As we begin programming, use your "Open File" menu to open the docs/index.html that camewith your NetLogo download, and click on the Primitives Dictionary, so that you can look upthe NetLogo language keywords as we use them. On my system, it looks like this.

We will build our model in four phases, in order to make learning a simple, step-by-step process.

Initialization: Building the "button" agents and randomly placing them on the display1.Behavior: Building the procedure that ties a pair of buttons together, merging their two sets of buttons.2.Control: Building the GUI elements that control the setup and execution of the simulation3.Data: Building the GUI elements that show the data gathered by the simulation4.

The majority of the programming is done in steps 1 and 2, while the buttons and graphs are added in steps 3 and 4.

Buttons Phase 1: The Button Turtles and the setup Procedure

From the File menu chose "New". This will give us a "blank" new model with an empty graphics window and a commandcenter. Use the File menu's Save command to save the model on your disk in a convenient place. We'll use the nameButtons, which is stored with the extension ".nlogo" automatically. Ours looks like this.


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Click on the Procedures tab where the model program is built. It will look like this. It has one line:

; add model procedures here

The ";" begins a comment which goes to the end of the line. We'll delete this and begin by building the buttons agents. Ourfirst phase simply builds 500 turtles (buttons) and randomly places them on the screen. The source file is here and looks likethis, where we've added line numbers for reference:

1 globals [buttons] ; Global variables

2 to setup ; Initializes model for new run.3 set-default-shape turtles "circle" ; Turtles are circles4 clear-all ; Reset turtles and patches5 set buttons 500 ; Set number of buttons to 5006 create-turtles (buttons) ; Create "buttons" number of turtles7 ask turtles [setup-turtles] ; Initialize each turtle8 end

9 to setup-turtles ; Called for each turtle during setup10 setxy random screen-size-x random screen-size-y ; Set our x,y randomly11 end

Cut and paste the source into the (empty) procedures tab. It will look like the image on the rightwhen your are done. Note the color coding used to make it easier to understand the elements ofthe Logo language. In this case, language commands, like "set" or "ask" are blue, built-invariables are purple, literal numbers and strings are red, our variables and procedures are blackand structural keywords (globals, to, end) are dark green.

To compile the code, click on the Compile icon, or simply click on the Interface tab where we aregoing next. Anytime you exit the Procedures tab, it will automatically compile if needed.

To run the current code, click on the Interface tab. We have not built a GUI yet so will have to use theCommand Center like we did in the "Kicking the Tires" introduction above. Make sure the type-in area ofthe Command Center is in "Observer" mode (i.e. the left of the type-in area shows "O >"). A smalldrop-down menu is used to change between Observer, Turtle, and Patches, see the introduction above.

Click in the type-in area to the right of the "O >" symbol and type "setup". You can do this several times,getting a new random set of buttons each time.

Line 1 declares the global variable, "buttons", the number of buttons for this run of the model. Note that it is not declared asan integer variable, which it happens to be. NetLogo dynamically types variables as needed. And indeed, you can have thesame variable be a string, a list, an integer and so on during the execution of the program. Look up "globals" in the NetLogoPrimitives Dictionary by clicking on the "G" Alphabetical index, or by scrolling primitives frame, or by searching to theword "globals" using your browser's "Find". Also note the comments at the end of the line: everything past a ";" is acomment, just like C/C++ "//" comments or the shell's "#" comments.

Lines 2 and 8 ("to" and "end") enclose the definition of the procedure "setup". Line 3 sets theshape of the turtles to be circles rather than the default arrow-like shape. Line 4 initializes thesystem by killing all existing turtles, resetting all globals, and clearing the patches and plots. This lets us re-run the model multiple times. Line 5 sets the global "buttons" to be 500. Line6 creates that number of turtles. Line 7 then causes the procedure on line 9 to be called foreach turtle.

For each of the commands above, there is an entry in the Primitives Dictionary in thedocumentation. To the right we show the "clear-all" entry. The "ca" in the banner tells us thatwe can use ca as an abbreviation for clear-all. The eye-ball tells us that it executes in theobserver context (as discussed in the Command Center above). If you have any doubt how acommand works, just look it up!


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The "ask" command is special: it executes the command in each individual turtle's context. Thisexposes variables like "color, xcor" which can be set, and "who", which cannot be changed.

The documentation contains special entries for these variables. To the right we show the entryfor turtles. You can also check the variables for patches. There are also predefined variablesfor constants like "red" , "pi", and so on.

Just as Lines 2 and 8 enclose the procedure "setup", lines 9 and 11 enclose the procedure "setup-turtles". Line 10 is our firstcompound command which contains three simple commands, two instances of the "random" command and one instance ofthe "setxy" command. Calling "random integer-variable" returns a number between 0 and (integer-variable - 1). The "setxy"command takes two variables and sets the turtle's xcor and ycor (coordinate) values to these two numbers. Note that Logotypically uses these compound commands, much like Lisp and other sophisticated recursive languages.

The "setxy" statement introduces us to the coordinate system used by the turtlesand patches. This is discussed in Tutorial #1 in the Changing Graphics WindowSettings section. The origin, x=0, y=0, is in the center of the patches. This causesNetLogo to have the screen-size-x and screen-size-y to be an odd number of cells.

But in the setxy command, we use screen-size which is twice the edge length plusone for the center! This works because NetLogo wraps the coordinates around theedges. So when an X coordinate is one greater than the right edge, it really on thefar left edge. This means the NetLogo modeling space is actually a torus. This iscommon in modeling frameworks.

A similar style is applied to colors. Colors go from 0-140 as discussed in Tutorial#2 in the Working With Colors section. If you set a color beyond the 140 colors,they wrap as well. Thus color 150 is the same as color 10. This lets us use colorsequal to the "who" number of the turtles without error.

Buttons Phase 2: Adding Behavior, the "Go" procedure

Our first phase simply let us initialize our Buttons model. This phase adds the model's behavior of selecting pairs of buttonsand tying them together, one pair each step of the model. The "go" and "joinClusters" procedures contain the new code weneed. This phase completes most of the programming, the additional phases are primarily GUI building. Here is the newsource code, again shown below with reference line numbers:

1 globals [buttons] ; Global variables2 turtles-own [group] ; Each turtle has "group" as a variable

3 to setup ; Initializes model for new run.4 set-default-shape turtles "circle" ; Turtles are circles5 clear-all ; Reset turtles and patches6 set buttons 500 ; Set number of buttons to 5007 create-turtles (buttons) ; Create "buttons" number of turtles8 ask turtles [setup-turtles] ; Initialize each turtle9 end

10 to setup-turtles ; Called for each turtle during setup11 set group who ; Initialize "group" ins var to ID built-in12 setxy random screen-size-x random screen-size-y ; Set our x,y randomly13 end

14 to go ; Step the model once15 locals [g1 g2] ; This procedure has some temp local variables16 set g1 group-of turtle random buttons ; g1 & g2 are two group values17 set g2 group-of turtle random buttons ; chosen from two random turtles18 ask turtles [joinClusters g1 g2] ; Merge group g1 with group g219 end


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20 to joinClusters [g1 g2] ; Convert group g1 turtles into g2 turtles21 if (group = g1) [set group g2 set color color-of turtle g2]22 end

As we did before, lets start with your placing the new source code in the Procedures tab,as shown on the right (replacing all the earlier code). Click on the Interface tab (whichauto-compiles the code) which lets us use the Command Center. As before, enter"setup" to initialize the model. You can also run "go" a couple of times. But note thismakes little in the way of change.

To run the model several times, use the "repeat" command which takes a count and aprocedure. We'll use "repeat buttons [go]" to run it the number of times we havebuttons. On the left we have the results of such a run. Note that a considerable numberof the buttons now belong to a large cluster.

Line 2 adds a new variable, "group", to each turtle, using the "turtles-own" command. This is initialized in line 11, inside ourearlier "setup-turtles" procedure, to be the value of the turtle's "who" variable. Recall "who" is automatically assigned toturtles and cannot be changed. Thus each turtle starts out in a group of one, itself. This means there are no threads yet tiedbetween any of the turtles. These two lines are the only changes to our earlier procedures. The other changes are to add the"go" and "joinClusters" procedures.

As before, lines 14, 19, 20 and 22 enclose our two new procedures using "to" and "end" pairs. At line 15, the "go" procedureuses the "locals" primitive to declare two local variables. Local variables are only "visible" within the defining procedureand are thus temporary to the execution of the procedure. Line 16 is a compound command, using the "set", "-of", "turtle",and "random" primitives. The execution is from right to left. First, "random buttons" returns an integer between 0 andbuttons-1. Next, the "turtle" primitive uses this to return the turtle who's ID ("who" value) is equal to that random number. Next, the "group-of" command returns the "group" variable's value of that particular turtle. (Look at the -of primitive in thePrimitives Dictionary, under "O".) Finally, the "set" command stores the result in the "g1" local variable. Line 17 simplyrepeats this for a second time to get a second group value, "g2", to use.

Whew! These three lines could have been written:

locals [g1 who1 t1 g2 who2 t2] set who1 random buttons set t1 turtle who1 set g1 group-of t1 set who2 random buttons set t2 turtle who2 set g2 group-of t2

But as you become more adapt at NetLogo, you'll find the terse form far easier to read and understand.

Line 18 in the "go" procedure asks each turtle to execute the command: "joinClusters g1 g2". JoinClusters is the firstprocedure we have created with arguments passed to it (g1 & g2). The task of "joinClusters" is to make every turtle in groupg1 become a g2 member by setting its group value to g2 and its color to be the same as all the turtles of g2. It does this witha single line with several parts. It is easier to understand rewritten as follows:

if (group = g1) [ set group g2 set color color-of turtle g2 ]

The "if" primitive takes a boolean (true/false) expression and if it evaluates to true, executes the supplied procedure. The ()'sare not necessary but improve readability. Note that "a = b" does not mean "set a to b" but "does a equal b". The first line ofthe if statement's procedure simply sets the group variable of the turtle to be g2. The second statement is a compoundstatement: turtle g2 returns the turtle who's ID ("who" value) is g2. We then set the color of the current turtle to be the colorof turtle g2. This is a bit subtle: "turtle g2" is guaranteed to be in the g2 group because of the way we initialized the groupsto be turtle IDs. Thus its color is the color of the g2 group. Actually, we could just as simply set the merged group colors tobe "red" or some other value. We are simply trying to make all the turtles in groups g1 and g2 to look alike.

Buttons Phase 3: Graphic Controls


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By now, we've done all the hard programming parts: built a set of randombuttons and built the procedure to pick up a pair of buttons and join theirgroups. Phase 3 and 4 are the graphic parts: providing controls and inputparameters, and providing outputs showing the results of the model.

You'll be delighted to hear that for this phase, we actually take two linesof code out of the program! We do this by placing a ";" in front of lines 1and 6 above, see the Procedures window to the left. Go ahead and dothis.

Initially this will cause an error, see Error window, right. Don't panic! Itsimportant to see how NetLogo handles errors, so lets dwell on this a bit.

When you commented out the two lines above, it left NetLogo not knowing about the"buttons" variable which tells us how many buttons to use. When you click to leave theProcedures tab, or you click the compile icon, NetLogo finds the error, and automaticallyopens the Error tab, with the error highlighted in blue, and explained in yellow. You can stillgo the Interface tab, but to help you remember you're in an error state, both the Procedurestab and Errors tab will be highlighted red.

So how do we fix the error? NetLogo's sliders both declare a global variable and set its value ..exactly the two lines we commented out. To make our own slider, go to the Interface tab andclick the slider control as shown on the right.

When we click on the slider control button, we are presented with a cross-hair cursor, askingwhere on the window to place the slider. After we click, we get an "empty" slider and anediting window.

On the right we show our entering "buttons" as the global variable name associated with thisslider, thus fixing the error. We also set 100, 100, 1000 as the Minimum, Increment, andMaximum values for the slider, and 500 for its current value. Go ahead and do this now. Afteryou are done, you can compile the program without error by entering the Procedures tab andclicking on the compile icon.

After creating the slider, it can be moved and resized by selecting it: click in the white part of the window and drag over theslider. By then clicking on the edit icon, you can also edit the parameters you set up when you made the slider initially.

At this point, you can run the program as you did in Phase 2: using the Command Center for entering "setup" and "go"commands, while using the slider to control the number of buttons used. The rest of this section will add two buttons toreplace this use of the Command Center

First, we'll add a NetLogo button to call "setup". To do this, in the Interface Tab, click the Button icon,and with the cross-hair cursor, click where you want to place the "setup" button. Put "setup" in theresulting dialog's code box. This will default to being the display name as well. Each click willre-initialize the buttons.

Similarly, create a "go" button, with the additional step of checking the "Forever" check box, causing it torepeat indefinitely (until the stop command above). We can now run the model easily without thecommand center.

Next, we'll generate graphical data for the simulation.

Buttons Phase 4: Graphical Results

To complete the simulation, we'll add three graphical data outputs: a plot of the number of buttons in the largest group, thecurrent tick count, and the current largest cluster. Here is the new source code which contains just 9 new lines. Save yourPhase 3 model and then cut and paste the new source into the Procedures window.

1 globals [ClusterSz ticks] ; Global variables2 turtles-own [group] ; Each turtle has "group" as a variable


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3 to setup ; Initializes model for new run.4 set-default-shape turtles "circle" ; Turtles are circles5 clear-all ; Reset turtles and patches6 set ticks 0 ; Initialize ticks global to 07 set ClusterSz 1 ; Initialize ClusterSz global to 18 set-plot-y-range 0 buttons ; Set Y axis to be 0 .. "buttons" tall9 create-turtles (buttons) ; Create "buttons" number of turtles10 ask turtles [setup-turtles] ; Initialize each turtle11 end

12 to setup-turtles ; Called for each turtle during setup13 set group who ; Initialize "group" ins var to ID built-in14 setxy random screen-size-x random screen-size-y ; Set our x,y randomly15 end

16 to go ; Step the model once17 locals [g1 g2 thisClusterSz] ; This procedure has some temp local variables18 set g1 group-of turtle random buttons ; g1 & g2 are two group values19 set g2 group-of turtle random buttons ; chosen from two random turtles20 ask turtles [joinClusters g1 g2] ; Merge group g1 with group g2

21 set thisClusterSz (count turtles with [group = g2]) ; Calculate merged size22 set ClusterSz (max list ClusterSz thisClusterSz) ; Update global max size23 plot ClusterSz ; Plot current max cluster size24 set ticks (ticks + 1) ; Keep track of number of steps25 if (ClusterSz = buttons) [stop] ; Stop if we have one huge cluster26 end

27 to joinClusters [g1 g2] ; Convert group g1 turtles into g2 turtles28 if (group = g1) [set group g2 set color color-of turtle g2]29 end

Compiling this code will not create an error. But when the "setup" button is clicked, we get a run-timeerror.

This is caused by our not yet having a plot window, thus the "set-plot-y-range" command fails. We'llsolve this by adding the NetLogo plot GUI item.

But first, lets look at the changes in the final version of the program's source code.

Line 1 adds two global variables we will use to monitor the simulation: "clusterSz" and "ticks". ClusterSz is the number ofbuttons in the largest group of buttons. We initialize this to 1 in line 7. Ticks is the number of times we've run the "go"procedure. We initialize this to 0 in line 6. Line 8 initializes the plot we are about to build to have the Y axis go from 0 tobuttons, the size of the largest cluster when all buttons are connected to each other.

Lines 21-25 manage clusterSz and ticks in the go procedure. Line 21 sets a local variable, "thisClusterSz", to be the size ofthe newly merged two groups of buttons. The phrase "turtles with [group = g2] returns the set of turtles who's group variableis g2. The "count" primitive returns the number of turtles in this set, which is used to set the value of thisClusterSz. Theglobal variable clusterSz is then set to the maximum value of itself and the local thisClusterSz. Line 23 adds the new value ofClusterSz to the plot. Line 24 simply increments the "ticks" global variable. Finally, line 25 halts the program when we'vereached the point where all the buttons are in the same group.

Just as with the slider, we click on the Plot icon, get a cross-hair cursor for placing theplot, and a plot editing window appears for setting the plot parameters.

We make four changes: fill in the Name to Cluster Size, X Axis Label to Steps, Y AxisLabel to Cluster and set the X Max Value to 1000.

To use the new plot item, click setup, then go, and watch the plot grow over time.


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To create the ClusterSz display, click on the Monitor icon, then clicking where you want to place thedisplay. In the resulting dialog, enter "ClusterSz" in the "reporter" box. (A Reporter in NetLogo is anyvalue or procedure returning a value).

Similarly create the "ticks" monitor which shows how many times the simulation "go" procedure hasbeen run.

To make the model clearer for the user, we'll clean up the layout a bit mymoving and resizing our GUI items, and adding two text items.

First, select and drag the buttons and slider down enough to leave a whitespace for a text label. Repeat for the two monitors and the plot, resizing theplot as shown. This separates the controls from the data items, leaving spacefor labels. Create two Text items describing the new layout, see details onthe right.

The final results appear like the image to the left.

Summary and Home Work!

In this fairly elementary (only 29 lines of code, after all!) NetLogo tutorial, we've tried several things:

Downloaded and installed the NetLogo system from the web.Ran two NetLogo simulations (Peer Net and Buttons) as applets from a web site.Used the Command Center to "kick the tires" .. exercise simple patch and turtle commands.Used the (excellent!) NetLogo documentation to learn the language and how models work.Created the Buttons simulation in four phasesLearned about both compile and run-time errors and how to solve them

Here are a few explorations you can try for your next steps into NetLogo

Add a "step" button which calls the "go" procedure, but only once rather than continuously.1.Look at the Information tab. Fill it out for this model. This will appear in the model if you send it to someone thereforeis very useful! And it will be included in the web page you are going to make in 5 below.

2.

Create the initial plot with an X axis length of 2*buttons. Thus if buttons is set to 700, the X axis will go from 0 to1400.

3.

Our current model lets multiple buttons exist on a single patch. Change the program to allow only one turtle to exist ona given patch (x, y location). Hint: use the "turtles-at" or "turtles-here" style commands. Or simply ask a randomnumber of patches to create the initial turtles. This is the "best practice" method.

4.

Use "Save as Applet" from the file menu. This will create an html file that will include the current model in the webpage as an applet, along with explanatory information as to how to deploy it. It will include the information from theInformation tab. Make sure you copy the NetLogoLite.jar file to where you put your applet! It contains the reducedNetLogo jar file appropriate for a web based model.

5.

Our current model can pick up the same button and connect it to itself! Change the program so that this does nothappen.

6.

Our current model randomly merges two groups of buttons. Change the model to merge the smaller group into thelarger one. Hint: use "count turtles with [..]" twice to figure out which of g1 or g2 is larger.

7.

Extra Credit: Most models have the agents move during the simulation. Using many of the above explorations, I've addedmotion to the model. In this version of the model, the two groups being joined together move towards each other if there isan empty space available. For your extra credit asignment, try using this version of the model, and read the code tounderstand how the motion was achieved.

Feel free to contact me if you run into difficulties or have suggestions for improving the tutorial!


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