Introduction to Computing for Complex Systems

(Lab Session 3)

Daniel Martin KatzMichigan State University

College of Law

A Few Books Worth Considering

Goals for Today

Finish Exploration of the Forest Fire Model

Begin exploration of theSchelling Segregation Model

Every item in our Model is:

Important Principles fromOur Last Session

(1) Defined within the Model

(2) Is a Primitive that is defined in the Netlogo Dictionary

OR

(remember we can think of primitives as the raw materials of models)

(such as in Globals, Breeds or in a subroutine)

Exploring the Forest Fire Model

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

(CONDT.)

The Forest Fire Model

The Forest Fire Model

3-D Forest Fire Model

(1) Modify the Color of the Forest to Blue

(2) Make the Fire Move North to South Instead of West to East

How Did We Do?

Modify the Color of the Forest to Blue

What Elements of the Code Do We Modify?

The Forest Fire Model

Procedures

The Forest Fire Model

Procedures

Make the Fire Move North to South Instead of West to East

Make the Fire Move North to South Instead of West to East

What Elements of the Code Do We Modify?

The Forest Fire Model

Procedures

The Forest Fire Model

Procedures

Try this Instead:

In what sense is this model random?

In what sense is this model deterministic?

Thinking conceptually about the model procedures

all of these models involve a mixture of determinism and randomness

In what sense is this model random?

Thinking conceptually about the model procedures

Placement of the patches

subject to the selected density level

Watch the Model in 3D

Watch the Model in 3D

Watch the Model in 3D

Watch the Model in 3D

In what sense is this model deterministic?

Thinking conceptually about the model procedures

The fire is really for G.U.I. purposes

result is basically already determined before the fire spreads

Back to the Forest Fire

Model Procedures

relies upon:if not any? stopask fires ask neighbors4fade-embersignitetick

The ‘To Go’ Procedure

if is a condition and you can think of it as:

if x condition is met than do action y

(otherwise move on to the next line)

The ‘To Go’ Procedure

This is going to kill the model if

condition is achieved

vs.

Forever Button

Once-only Button

The ‘To Go’ Procedure

Why is this Arguably the KEY piece of code?

What does it mean in plain english?

The ‘To Go’ Procedure

What is neighbors4?

Remember our basic rule:

The ‘To Go’ Procedure

It is defined within the program

or it is one of the netlogo primitives

The ‘To Go’ Procedure

Neighbors and Neighbors4

turtle turtle

neighbors4 neighbors(think of

this as the 8 neighbors)

turtle

(a) we are asking “fires”

The ‘To Go’ Procedure

(b) to ask their 4 neighbors

(c) the 4 neighbors that are green

(d) to run the “ignite” protocol

(e) and then set their breed to embers

(f) now run the “fade-embers” protocol

The ‘To Go’ Procedure

The ‘To Go’ Procedure

The ‘To Go’ Procedure

When is this finally going to halt?

It is a forever button which can be halted using “STOP”

“STOP” is triggered when the “if” condition is satisfied

Lets Discuss Some Extensions of The Forest Fire Model

Extensions of The Forest Fire Model

What are the actual dynamics that generate and sustain forest fires?

What else could we incorporate into this model?

A Non-Exhaustive List

Differential Levels of Moisture

Variable Terrain (Rivers, etc.)

Prior Interventions (Firewalls, etc)

Wind and other Weather Patterns

Some of the Existing Extensions

different forms of implementation may impact the results

Implementation Matters

different forms of implementation may be more qualitatively appropriate

sophistication regarding implementation allows you to be a more critical consumer of scholarship

the neighbors4 example

Neighbors and Neighbors4

turtle turtle

neighbors4 neighbors(think of

this as the 8 neighbors)

turtle

Neighbors and Neighbors4

neighbors(think of

this as the 8 neighbors)

what did the implementer of the model decide?

neighbors4

decided that the fire could not move diagonally

this is probably not qualitatively reasonable

Step 1: map the dependancies

Step 2: learn the syntax and functionality for all unknown primitives

Protocol to Decode 3rd Party Implementation

Step 3: read each line of code and determine what it doing

Mapping of the Code

just some examples of primitives from the dictionary that we have already learned

Protocol to Decode 3rd Party Implementation

Next We Went Line by Line Through the Code

Step 4: sketch a procedures map that follows the chronology of your program

There is one additional step that often proves useful

Protocol to Decode 3rd Party Implementation

Particularly when you are writing a model from scratch

Very Rough Sketch of the Fire Procedures Map

(1)

(2) (1)(a)(i)

(1)(a)

(1)(a)(ii)

(1)(b)

the point is just to aid in your understanding

(2)(a)

(2)(a)(i)

(2)(a)(i)(I)

(2)(b)

(2)(b)(i) (3) - End

Loop Until “if”

Condition is met

The Value for Global Must Get “Set” Somewhere in the Model Procedures

Globals -- one other note

Mapping of the Code

Introduction to theSchelling

Segregation Model

What Does this Title Mean?

What is the micro to macro disconnect?

relationship to the ecological inference

fallacy?

Schelling Social Segregation Model

Schelling Social Segregation Model

Schelling Social Segregation Model

Schelling Social Segregation Model

Schelling Social Segregation Model

Schelling Social Segregation Model

Schelling Social Segregation Model

versus

note: stopped model before % unhappy = 0

Schelling Social Segregation Model

Test these Parameters and report

Results

Schelling Social Segregation Model

Schelling Social Segregation Model

Schelling Social Segregation Model

Schelling Social Segregation Model

versus

Schelling Social Segregation Model

the full model

Print This and Draw the Connections for a Full Map

of the Schelling Code

Mapping of the Schelling Code(%-similar-wanted is a slider)

Learn the Syntax and Functionality for all unknown Primitives

(starting with “to setup”)

Again this is the conditional “if” statement

It is relying upon “number”

Is number a netlogo primitive?

It is the name of the slider

How could I rename this “totalagents”?

Take 5 minutes and Try to Figure it out

(1) Right Click (ctrl + Click on Mac)

on the “number” slider

(2) change the global variable name from “number” to “totalagents”

Modifying the name (or values) of a Slider

Modifying the name (or values) of a Slider

Notice the error Message

Must Change all instances from “number”

to “totalagents”

Then double check by hitting

the “check” Button

We have learned a small exception to our rule

Revised Rule --> everything in the model:

(1) defined somewhere in the code (2) is a primitive (3) it is something like a slider

What is this doing in plain english?

clear everything

if the end user selects a slider value that exceeds the number of patches

tell that end user to modify and try again

(1) Close Netlogo

(2) Discard the Changes

(3) Restart the Segregation model

Quick Reset

Open the SchellingSegregation Model

Delete all procedures except those shown to left

What is has this done to the model?

<Only Red Turtles>

<“Go” button is red>

What is this doing in plain english?

asks all of the patches

to randomly “sprout” 1 turtle per patch

and make that turtle color = red

What is this doing in plain english?

now take half of those turtles

and set turtle color = green

We Need to see What “update-varables” is Actually Doing

Here we are going to “set” some of our “turtles-own” variables

“Set” the Turtles-own Variable “similar-nearby”

to the count of “turtles-on” neighbors (8 of them)

but only those with color = my color

“Set” the Turtles-own Variable “similar-nearby”

to the count of “turtles-on” neighbors (8 of them)

but only those with color = not my color

Take a look at what is happening here

The “happy?” condition is going to be important

involves an agent by agent comparison of the spread between “similarity-wanted” & “similar-nearby”