Introduction to Computing for Complex Systems

(Lab Session 4)

Daniel Martin KatzMichigan State University

College of Law

Take a Look at this Article

from the Economist

(July 22, 2010)

Agent Based Models and

Positive Economic Theory

Refer Back to my slides about equilibrium and its discontents

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)

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 “other-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”

Now Lets Look at “Update-globals”

It involves “lets” and “sets”

uses the globals but also some of the turtles-own variables

I will allow you to review this on your own

However, consider the syntax of “sum”

(1) Right Click (ctrl + Click on Mac) on the “percent-similar” plot

(2) This will appear and will allow for various modifications(color, interval, etc.)

We now consider the “to go” portion of the code

lets reduce the “to go” procedures

the “to go” portion of the code

above are the major new elements

remember conceptually the model relies upon movement if a turtle is unhappy

Again, we have the “if”

the “to go” portion of the code

The “to go” button with stop when all turtles are “happy?”

Here is how “Happy?” gets set:

model continues to tick until every agent is above the “%-similar-wanted” as set on the slider

create an agentset of “not happy?” turtles

the movement portion of the code

For that agentset we run the “find-new-spot” procedures

We know from the “to go” procedures that this is going to continue to run until the “if” condition is satisfied

the movement portion of the code

the movement portion of the code

the movement portion of the code

Notice that it is going to re-run the “find-new-spot”

If the “if” condition is met

In other words, agents are going to move until they find a open patch

then agent will occupy the center of open patch

Thinking about Extensions to the Schelling Model

This is closer to a “representative agent” model

Agents are homogenous in their %similar-wanted

In reality, there is likely variance across agents

In other words, comparing across agents there are differential preferences with respect to the %similar-wanted

Thinking about Extensions to the Schelling Model

spatial considerations

The 8 neighbors might not be how individuals actually make their assessments

agents might make choices based upon a wider assessment of the neighborhood

there might be different “prices” for different patches (i.e. a simulated housing market)

Thinking about Extensions to the Schelling Model

structural considerations

the model could encode certain barriers to entry to particular neighborhoods

barriers could be highly asymmetric(i.e. red turtles face no barriers and green turtles face high barriers)

An Exercise

Start With the Default Implementation of

Social Segregation

Imagine that you are interested in

developing a certain style of integration

Modify the Code as Needed in Order to Produce The Closest Possible Model Run to the Camouflage

Note: this involves 4 Groups not 2 Groups

Your Goal!

An Exercise

Send Me Your Best Effort

katzd@law.msu.edu

I will announce the Winner

Simple Birth Rates

Simple Birth Rates

Simple Birth Rates

Simple Birth Rates

take a few minutes and play around with the model

consider the questions offered above

Thinking Conceptually:Simple Birth Rates

What Does the Turtle Movement Add to the Model?

Are Turtles Added to the Model? and If So How?

Are Turtles Removed from the Model? and If So How?

Simple Birth Rates:Exploring the Code

Step 1: map the dependancies

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

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

Simple Birth Rates

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

At this point it is more Important for you to go though the models line by line on your own using

the above protocol

Simple Birth Rates

Experiment

Basic Setup

Simple Birth Rates

Death

Plots

Reproduction

Movement

Simple Birth Rates

“To Setup” Procedures

Simple Birth Rates

“To Go” Procedures

Simple Birth Rates

Turtle Movement Procedures

Simple Birth Rates

PleaseReview “ifelse”

How does it work?

Simple Birth Rates

Take a Look at the

Reproduction Procedures

Simple Birth Rates

Death Procedures

Plot Procedures

Simple Birth Rates

Right Click (ctrl + Click on Mac) on the “run experiment” Button

Simple Birth Ratesforever button

Notice observer is selected

Calls upon the go-experiment

sub-procedures

Name of our Button

Simple Birth Rates

Take a look at this for later in the week

Automation is really going to help us