agent-based modelling and simulations · prof. agostino poggi netlogo university of parma - 2...

Agent-Based

Modelling and Simulations

NetLogo

Agostino Poggi

University of Parma - 2NetLogoProf. Agostino Poggi

Introduction

♦ is a programmable modeling environment for simulating complex systems

♦Modelers can give instructions to hundreds or thousands of independent agents operating in parallel

♦Was created by Uri Wilensky in 1999

♦Current release is 5.2


System Features

♦Cross-platform

Runs on different operating systems (e.g., Windows, Linux, MacOS, …)

♦Web-enabled

Runs within a web browser, but can be download and run locally

♦Models can be saved as applets to be embedded in web pages


Language Features

♦ Is fully programmable

♦Has a simple language structure

♦ Is a Logo dialect extended to support agents and parallelism

♦Supports a unlimited numbers of agents and variables

♦Supports double precision arithmetic

♦Provides many built-in primitives


Agents

♦The world is two dimensional and is divided up into a grid of patches

♦Patches are agents that represent a square piece of the world over which turtles can move

♦Turtles are agents that move around in the world

♦ Links are agents connecting pairs of turtles

♦The observer is an agent that can create turtles and have read/write access to all the agents and variables


Patches (1/2)

♦Have a color defined by the pcolor variable

♦Have a location defined by the pxcor and pycorconstant variables

♦The patch in the center of the world has coordinates (0, 0)

♦The total number of patches is determined by the max-pxcor - min-pxcor and max-pycor - min-pycorpairs of variables

♦Usually every patch has the same number of neighbor patches (toroidal world)


Patches (2/2)


Turtles

♦Have an index defined by the who variable

♦Have a color defined by the color variable

♦Have a location defined by the xcor and ycorvariables Its value can be a decimal number: it can be positioned

at any point within a patch, default position is the center of the patch

♦Have a direction defined by the heading variable Its value is a number greater than or equal to 0 and less

than 360 (0 is north, 90 is east, …)

♦Can be divided in breeds

♦The total number of turtles is determined by the count turtles command


Links

♦Represent “edges” on networks

♦Can “move”, “die”, “grow”, …

♦Have a start node and an end node represented by two turtles

♦Can be directed or undirected

♦Can be divided in breeds

♦Can have different colors, thickness, …


Observer

♦Can create new agents and controls

♦Gives commands to patches, turtles and links

♦Can change the values of variables

♦Can produce information about the state of the simulations

♦ Is the interpreter between the user and the agents


Breed

♦Allows to defines a subtype of turtles and links

breed [wolves wolf]

breed [sheep a-sheep]

directed-link-breed [unis uni]

undirected-link-breed [bis bi]

♦Each turtle has a breed variable

if breed = wolves [ ... ]

♦Each turtle can change breed

set breed sheep

♦Each breed can a specific default shape

set-default-shape wolves “wolf"


Agent Set

♦ Is an homogeneous set of agents

♦Some agent sets are defined by NetLogo environment

turtles, patches and links

♦Subset of turtles, patches and links are defined by the use of some specific commands

♦ Agent sets are assigned through the commands

turtle-set, patch-set and link-set


Data Types

♦Number values are used for defining calculations and are all floating point numbers

♦ Boolean values are used for defining conditions and correspond to the true and false constants that can be combined with the and, or, not and xor operators

♦ String values are used for defining names and represent immutable sequence of characters that are create with double quotes and concatenate with the word command


List

♦Allows to store multiple pieces of information in a single value

♦Each piece of information can be values of anypossible type (i.e., a boolean, a number, a string, an agent, an agent set or even another list)

♦Pieces of information are enclosed between squarebrackets

♦Each piece of information is identified by an integer starting at 0


Variables

♦Each turtle, patch and link has its set of variables

♦Some variables are defined by NetLogo environment

♦The turtles-own, patches-own and links-own keywords allow to define new variables

turtles-own [ energy speed ]

♦Variables value can be modified using the set command

set color red

set pcolor red

♦A turtle can also read and set variables of its patch


Global & Local Variables

♦ If a variable is a global variable, there is only one value for the variable and all the agents can access it

♦A variable is made global by using the globalskeyword at the beginning of the program code

globals [ clock ]

♦Moreover, it is made global by adding at the interface level either a switch or a slider

♦Global variables can by read and set at any time by any agent

♦ Local variable are defined inside procedures

let limit 10


Tick Counter

♦Usually simulations are discrete and time passes in discrete steps defined by a built-in tick counter

♦The tick command advances the tick counter by 1 and usually also update the view

♦The clear-all command clears the tick counter along with everything else

♦The reset-ticks command resets only the tick counter

♦The current value of the tick counter is provided by the ticks report and is shown in the NetLogo GUI above the view


Turtles Creation

create-turtles 10

♦Asks the Observer to create 10 turtles

create-wolves 10

♦Asks the Observer to create 10 wolves

sprout 10

♦Asks the current patch to create 10 turtles

hatch 10

♦Asks the current turtle to create 10 turtles


Links Creation

create-link-with turtle 2

♦ Creates an undirected link between the caller and turtle 2

create-link-to turtle 2

♦ Creates a directed link from the caller to turtle 2

create-link-from turtle 2

♦ Creates a directed link from turtle 2 to the caller

create-bi-with turtle 2

♦ Creates an undirected link (bis breed) between the caller and turtle 2

create-uni-to turtle 2

♦ Creates a directed link (unis breed) from the caller to turtle 2


Agent Set Creation (1/2)

other turtles

♦All the turtles excluding the current

turtles-here

♦The turtles on the current patch

other turtles here

♦The turtles on the current patch excluding the current

patches at-points [[1 0] [0 1] [1 0] [0 1]] (neighbors4)

♦The patches around the current patch

turtles-on neighbors

♦The turtles standing on the eight surrounding patches


Agent Set Creation (2/2)

turtles in-radius 3

♦The turtles less than 3 patches away

patches with [pcolor = red]

♦All the red patched

other turtles here with [color = red]

♦The other red turtles on the current patch

turtles with [(xcor>0) and (ycor>0)and(pcolor=green)]

♦The green turtles with coordinates greater than 0

[mylinks] of turtle 0

♦The links connected to turtle 0


Agent Set Uses (1/3)

ask turtles [ die ]

♦Makes all the agents in the set do something

ask one-of links [ die ]

♦Picks a random agent from the set

ask min-one-of turtles [energy] [ die ]

♦Picks the agent in the set with min/max of some attribute

show count turtles

♦Finds out exactly how many agents there are in the set



show mean [energy] of turtles with [color = red]

♦Computes (mean, median, min, max, sum, standard-deviation, variance) over some attribute of the agents in the set

if any? turtles [ show count turtles ]

♦Sees if the set of agents is empty

if member? self turtles [show "Yes, it's member !"]

♦Sees whether the current agent is in a set

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

♦Sees if all the agents in a set satisfy a condition



histogram [color] of turtles

♦Makes a distribution histogram of a variable in a set

ask (turtle-set self turtle 2 turtles with [color = red])

[ die ]

♦Creates new sets from other sets and individual agents

if (set1 = set2) [show "Identical sets !"]

♦Compares (=, !=, <, >) two sets


Working with Lists (1/4)

set mylist [2 7 5 Bob [3 0 -2]]

♦Creates a constant list

set random-list list (random 10) (random 20)

♦Creates a list of two random integers

set mylist replace-item 2 mylist 10

♦Replaces the third item of mylist with 10

set mylist lput 42 mylist

♦Adds 42 as last item of mylist



set mylist fput 12 mylist

♦Adds 12 as first item of mylist

set mylist but-last mylist

♦Removes the last item from mylist

set mylist but-first mylist

♦Removes the first item from mylist

foreach mylist show

♦Shows the items of mylist



map round [1.2 2.2 2.7]

♦ Builds the list [1 2 3]

map [? * ?] [1 2 3]

♦ Builds the list [1 4 9] (? Means the current item)

member? 2 [1 2 3]

♦ Checks if 2 is member of the list [1 2 3]

position 2 [1 2 3]

♦Gets the position of 2 in the list [1 2 3]



sort turtles

♦Builds a list of turtles sorted in ascending order by whovariable

sort-by [[size] of ?1 < [size] of ?2] turtles

♦Builds a list of turtles sorted in ascending order by sizevariable

list [1 2 3] [4 5 6]

♦Builds the list [[1 2 3] [4 5 6]]

sentence [1 2 3] [4 5 6]

♦Builds the list [1 2 3 4 5 6]


Commands & Reporters (1/3)

♦Commands are actions for the agents to carry out

♦Reporters carry out some operation and report a result either to a command or another reporter

♦Commands and reporters defined by NetLogoenvironment are called primitives

♦User’s defined commands and reporters are called procedures



♦Procedures can take inputs value

♦Each procedure is composed of

The keyword to or to-report

The name of the procedure

The optional arguments

A sequence of commands

The keyword end

♦After its definition, a procedure can be used elsewhere in the program


Conditionals


Loops


File I/O (1/3)

file-open myfile.txt

♦Opens a file

file-close

♦Closes a file

file-close-all

♦Closes all the files

user-file

♦Opens a window for opening a file

user-new-file

♦Opens a window for creating a file


File I/O (2/3)


File I/O (3/3)

file-read

♦Reads the next token in the file and interprets it in the appropriate type

file-read-line

♦Reads the next line in the file as a string

file-read-characters 4

♦Reads the next 4 characters (including newlines and spaces) in the file as a string

file-at-end?

♦Checks if there are no more characters left to read in the current file


Graphical User Interface

toolbar

Allows to give “on the fly” commands to agents


Toolbar Elements (1/2)

Button Allow the execution of a procedure

Slider Is a global variable which is accessible by all agents

Switch Is a visual representation for a true/false global variable

Chooser Allows to choose a value for a global variable from a list

of choices

Input Is a global variable that contains a string or a number

Monitor Displays display the current value of a variable

Plot Displays the history of the value of a variable

Output Is a scrolling area of text which can be used to create a

log of activity in the model

Note Allows the addition of text labels to the Interface tab


Toolbar Elements (2/2)

button

switcher

slider

output

plot


Code View


Interface View (1/3)


Model Setting


Info View


Model Library


Turtle Shape Editor


A Multi-Colors World (1/2)

patches-own [ soil-type ]

to setupclear-allask patches [

set soil-type random 4ifelse soil-type = 0 [ set pcolor YELLOW ] [ ifelse soil-type = 1 [ set pcolor RED ]

[ ifelse soil-type = 0 [ set pcolor GREEN ][ set pcolor BLUE ]

]]

]end


A Multi-Colors World (2/2)


Population Evolution (1/3)

breed [persons person]

persons-own [ age ]

to setupclear-allset-default-shape persons "person“reset-ticks

end

to go…

end



to gocreate-persons 10 [

set xcor random-xcorset ycor random-ycorset color REDset age 0

]

ask persons [ set age (age + 1) ]

ask persons with [age > 10][ die ]

tickplot count persons

end


Random Turtle Movement (1/2)

to setupclear-allcreate-turtles 100reset-ticks

endto go

ask turtles [fd 10 rt random 10 lt random 10 show absolute-value xcor ]

tickendto-report absolute-value [number]

ifelse number >= 0 [ report number ] [ report (- number) ]end


Random Turtle Movement (2/2)


Prey Predator Model (1/7)

breed [sheep a-sheep]breed [wolves wolf]

sheep-own [ age ]wolves-own [ energy age ]

to setup...

end

to go...

end



to setupclear-allset-default-shape sheep "sheep"create-sheep initial-sheep [

set color whiteset size 1.5 setxy random-xcor random-ycorset age 0 ]

set-default-shape wolves "wolf"create-wolves initial-wolves [set color brownset size 1.5setxy random-xcor random-ycorset age 0set energy random (3 * energy-per-sheep-eaten)

]reset-ticks

end



to goif not any? turtles [ stop ]ask turtles [ take-a-step ]ask sheep [ try-to-make-bunnies ]ask wolves [set energy (energy - 1)try-to-eattry-to-make-kittens ]

ask turtles [set age (age + 1) ]ask sheep [ if age > max-sheep-age [ die ] ]ask wolves [if age > max-wolves-age [ die ]if energy < 0 [ die ] ]

tickend



to take-a-stepright random 50left random 50forward 1

end

to try-to-make-bunniesif random-float 200 < sheep-birth-rate [

hatch-sheep 1 [rt random-float 360fd 1set age 0 ]

]end



to try-to-eatlet prey one-of sheep-hereif prey != nobody [ask prey [ die ]set energy energy + energy-per-sheep-eaten ]

end

to try-to-make-kittensif energy > wolves-energy-to-reproduce [hatch-wolves 1 [rt random-float 360fd 1set age 0set energy energy / 2 ]

set energy energy / 2]

end


Walking on a Network (1/4)

breed [nodes node]breed [walkers walker]

walkers-own [location]

to setup…

end

to layoutlayout-spring nodes links 0.5 2 1

end

to go---

end

Resistance to change in their length for a change of 1 unit

Zero force length

Repulsion force that 2

nodes at a distance of 1 unit

will exert on each other



to setupclear-allset-default-shape nodes "circle"create-nodes 30 [ set color blue ]ask nodes [ create-link-with one-of other nodes ]repeat 500 [ layout ]ask nodes [ setxy 0.95 * xcor 0.95 * ycor ]create-walkers 5 [

set color redset location one-of nodesmove-to location

]reset-ticks

end



to goask links [ set thickness 0 ]

ask walkers [let new-location one-of [link-neighbors] of location

ask [link-with new-location] of location [set thickness 0.5 ]

face new-location move-to new-locationset location new-location

]

tickend

agent-based modelling and simulations · prof. agostino poggi netlogo university of parma - 2...

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