NetLogo Workshop - Wayne State University

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Transcript NetLogo Workshop - Wayne State University

Slides and model files will be at > NetLogo workshop

NetLogo Workshop

Complexity And Business Analytics October 10, 2008, UM-Dearborn David Bowen, WSU Physics [email protected]

As a result of this workshop, (I hope) you will be able to:

12:30 – 2:10 • Describe agent-based modeling • Download & install NetLogo • Find & use existing models installed with NetLogo & on NetLogo website 2:30 – 4:10 • Modify an existing NetLogo model • Build a new NetLogo model 10/10/08 NetLogo Workshop 2

NetLogo Workshop

Part 1 • Agent-based modeling • Download and Install • Find and run

Agent-Based Modeling

• What is agent-based modeling?

 Simulating a set of acting/interacting agents  Examples of agents: people, organs, molecules, planets, family units, corporations, ribosomes  Modeler assigns (programs): o Characteristics or properties of agent  Homogenous or diverse agents o Rules or methods of interaction  Example: Preferentially link to the most popular agent (the one that already has the most links) 10/10/08 NetLogo Workshop 4

Agent-Based Modeling

• What is agent-based modeling?

 Agent-based modeling environment/toolkit: o Steps agents through actions/interactions o Displays agents, charts indicators, saves data  NetLogo has four basic types of agents A: always o A Observer: sees all o A Turtles (agents), modeler can create subtypes o S Links between turtles, can have subtypes o A Patches or pieces of background  Can be “invisible” but sometimes important (grass in Sheep and Wolves) 10/10/08 NetLogo Workshop 5

Agent-Based Modeling

• Where is agent-based modeling used?

  Everywhere, e.g. all academic departments Natural systems (science, engineering etc.) o Many existing simulation techniques, question is purpose, strengths, weaknesses  Social systems (humanities, social science, business/marketing etc.) o Often the best or only laboratory available 10/10/08 NetLogo Workshop 6

Agent-Based Modeling

• Types of use  Real-world simulation, optimization   Research Classroom: learning, demo, homework • Alternatives to making your own models   Models Library downloads with installation Publicly available models  Modify and existing model 10/10/08 NetLogo Workshop 7

Agent-Based Modeling

• About NetLogo  Uri Wilensky et al. at Center for Connected Learning and Computer-Based Modeling at     Northwestern University “Low floors, high ceilings” Free download Java-based (run anywhere) but private Java copy Discussion forums, technical support, continuous development 10/10/08 NetLogo Workshop 8

Download and Install

• URL: • Notice: mail lists, Resources (more models) • Download on the left • Save to desktop (because of rights on these computers, elsewhere you can accept the default) • Double-click on downloaded file to install (NetLogo4.0.3Installer.exe) • Location: up-arrow to desktop, add


NetLogo > Next • Accept all other defaults 10/10/08 NetLogo Workshop 9


• Start > All Programs > NetLogo > NetLogo 4.0.3

• Notice:   File menu item (top left) – Models Library, etc Interface – “the model”   Information – How to use & change the model Procedures – the code 10/10/08 NetLogo Workshop 10

Models Library

• File > Models Library   Checked except for (unverified) • Biology > Heatbugs (famous) Double-click model name or picture to open    Setup then Go (Go again pauses) Information – what the model is doing Procedures o Turtles-own establishes properties (characteristics) o Button name starts “to” procedure with that name o ; for comment, can be whole or last part of line 10/10/08 NetLogo Workshop 11

Models Library

• File > Models Library > Computer Science > Cellular Automata > Life • Cellular Automaton  Here, patches = cells, no turtles o Dark = cell alive, background color = dead   Cell with 3 live neighbors comes to life Live cell with two live neighbors continues to live o Otherwise cell dies 10/10/08 NetLogo Workshop 12

Models Library

• Social Science > Party (famous in another form)  Schelling model – two types of people o Here, men and women o Originally, Black and White o Otherwise the same – properties and methods  How comfortable are these agents with those of the other type – slider  Even a slight preference can lead to complete segregation 10/10/08 NetLogo Workshop 13

Models Library

• File > Models Library > Networks > Small Worlds (famous – six degrees of separation)  Uses links  Path along links from one agent to another  Setup = ring, links to 2 nearest on each side   Average path length for all pairs of agents Even a few links across the ring reduces the  average path length significantly Significant in organizations, e.g. businesses 10/10/08 NetLogo Workshop 14

Models Library

• File > Open > Biology > Wolf Sheep Predation • Different kinds of agents, including patches • Click grass? Switch to On • Boom-and-bust cycles very common 10/10/08 NetLogo Workshop 15

Models on NetLogo site

• URL: > Community Models • Possible problems if models are written for earlier versions of NetLogo   My Two-color gas works with 4.0.3

My Brownian motion doesn’t 10/10/08 NetLogo Workshop 16

NetLogo Models on the Web

• • Solves problems with old versions since Java Virtual Machine (VM) downloaded also (but different versions can coexist) Models   Brownian motion works Big Bang model > Classroom

Other things NetLogo can do

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• Array, Table, GoGo, Profiler, GIS, Sample, and Sound are in the standard installation • In Extensions subfolder of NetLogo installation folder • Each is explained in Help > NetLogoUser Manual > Extensions • Some (GIS, Table) come with existing models 10/10/08 NetLogo Workshop 18

NetLogo Workshop

Part 2 • Modify • Roll your own

Programming Resources

• Help > User Manual  Tutorials  Interface Guide – World, Menu items, Controls o World - Settings: size, wrapping Vs reflecting  Programming Guide – big picture o Types: observer (starts off), turtle, patch, link o What can I do with agents?

 NetLogo Dictionary – the nitty gritty o Alphabetical list o By type 10/10/08 NetLogo Workshop 20

Modify One

• File > Model Library > Computer Science > Cellular Automata > Life • Procedures – scan to numbers 3 and 2 • On the way  patches-own – creates properties for patches o Built-in: pxcor, pycor, pcolor o living? - ? makes this logical (true/false only) • 3  4, 2  3 • File > Save As a new name, e.g. LifeDB on desktop 10/10/08 NetLogo Workshop 21

Modify Life

• Add a slider to vary number on interface • Click on down-arrow to select slider  Global variable init-number, 1 to 5, value 2  Then right-click to Select, squeeze it in • In Procedures, 2  3  init-number, init-number + 1 / Save, Setup then Go 10/10/08 NetLogo Workshop 22

Modify Life

• You now load this modified version from the desktop or by double-clicking the desktop icon  “Back home” you can keep the .NLOGO file in any folder you choose 10/10/08 NetLogo Workshop 23

Modify Small Worlds

• File > Models Library > Networks > Small Worlds • On interface, put in a slider:  Global variable init-links   Minimum 1 Increment 1   Maximum 3 Value 2 • Save on desktop under a new name  Add initials?

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Modify Small Worlds

• Procedures, scroll through (bigger than Life)  Find to setup, then see make-turtles then wire-them (this creates the links)   About 75% down (Find?) find to wire-them What we want to do: o Always link to n+1 o If init-links = 2 or 3 then also link to n + 2 o If init-links = 3 then also link to n + 3  Dictionary: if condition [ commands ] 10/10/08 NetLogo Workshop 25

Modify Small Worlds

• Error when running with init-links = 1; divide by zero  Divide by clustering-coefficient-of-lattice  divide by dum, protect dum from being zero o We might eventually want a better fix 10/10/08 NetLogo Workshop 26

Modifying Models

• Find a model that does something close to what you want, and modify it to suit • For these modified models, we should go back and update the information • Structured and commented code helps – do this for yourself, too 10/10/08 NetLogo Workshop 27

Roll Your Own

• Decisions needed   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?

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• You might want to change the World settings   Size Location of 0, 0   Wrapping or box Patch size (also determines size of world screen) 10/10/08 NetLogo Workshop 29

Programming in NetLogo

• Case-insensitive • To set a equal to b: set a b • Arithmetic operators must have space on either side: set a 3 * b • Can use parentheses to control order • Use [ ] to block code statements • White space ignored after minimum space • Routines start with to, end with end • No number types • Logical variables end in ?

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Programming in NetLogo

• Context: who is acting?

 ask turtles [ commands ] sets context to turtles o Agents can ask other agents or even other types of agents  ask turtles [ … ask links [ … ]… ]   Only that particular agent can find the value or change a value that it owns If one agent (e.g. a turtle) is acting, other turtles is set of all other turtles, one-of other turtles is a random other  stop to stop asking • breed to subtype an agent: breed [ cats cat ] 10/10/08 NetLogo Workshop 31

Simple Model

• Model will:  Setup o Create turtles with random headings (this is the default), positions, speed  Go o Let turtles go with speed and headings o Randomly change speed and headings  Sliders to control speed range and size of heading changes 10/10/08 NetLogo Workshop 32

Simple Model

• Built-in turtle variables (each turtle has its own)  breed (sub-type)  Color (defaults to random for each turtle)         Heading (degrees, 0 = up, 90 = right) hidden?

label, label-color pen-mode, pen-size shape size Who (a number) xcor, ycor (by default 0, 0) 10/10/08 NetLogo Workshop 33

Network Model

• Model will:  Setup o Create a set of turtles with random positions o Create a random set of links between the turtles  Each turtle has same chance of having links  Go Once o Pick a random turtle and a random one of its links, and replace it within one attached preferentially  Higher chance of linking to a turtle with the most links 10/10/08 NetLogo Workshop 34

Network Model

• Start new model, save it to desktop as Network • Go to Model Library, open Network > Preferential Attachment, copy layout and limit-magnitude to clipboard and then into Procedures window, and resave  Will make a better World plot 10/10/08 NetLogo Workshop 35

Network Model

• Agentset – a list set of agents  Defaults to a random order but can be sorted  Can be “traversed” – go through all agents in   the list by asking Can also pick a random agent from the list If we want angentset to persist, must set it to a name we have previously declared in globals or locally • If we have picked a turtle, other turtles is an


of all of the other turtles 10/10/08 NetLogo Workshop 36

Agentsets and Lists

• Agentset: an unordered set of agents of any type, including breeds  Order is randomized on each use   Can ask agentset [ list of commands ] Current agent in “ask” sequence: self • List: an ordered list of any objects, including agents  Order is always the same unless you change it   Can be sorted, etc.

Current list item in “for each” sequence: ?

Return to slide 36

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• Transport • Agents jump by patches left to right • Have to wait at each patch for its individual wait count, can’t jump on top of another • Setup:  Initialize patches with wait counts, color-code • Go:  Turtles jump to right if wait count reached and that patch is empty  After jumping off last patch on right, turtle dies 10/10/08 NetLogo Workshop 38


• 3D • Numerical modeling (modeling number of agents, etc.)

• Flying behind a turtle


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