Downloads

• NetLogo version of Schelling’s segregation model:
  • Download page or
  • https://ees4760.jgilligan.org/models/class_24/class_24_models.zip
  • https://ees4760.jgilligan.org/models/class_24/segregation.nlogo

Model Overview

• Turtles represent households.
  • Two colors of turtles: red and blue
  • Turtles have one state-variable: happy? (true or false)
• There is a global variable %-similar-wanted and a turtle is happy? if at least this fraction of its neighbors have the same color as its own.
• At each tick, unhappy turtles move to a random empty patch.
• When all turtles are happy?, the model stops.

Experiments

Vary %-similar-wanted and the density of turtles on the patches.

Suggestions:

• Try extreme values of parameters:
  • Set density and %-similar-wanted to different combinations near maximum, minimum, and in the middle.
  • What do you see?

Extreme Values

• Set density to 75% and set %-similar-wanted to 95%
• Press setup and then press go
  • What happens?
• Now, with go still pushed, slowly reduce %-similar-wanted.
  • Now what happens?

Systematic experiment:

• Using Behaviorspace, create a new experiment to vary %-similar-wanted
  • Set time limit to 1000
  • Set density to 75
  • Measure percent-similar
• What do you see?
• Try adjusting both %-similar-wanted and density

Visualizing Structures

• Add the following to the procedure to update-turtles, after set happy?

  ifelse happy? [ set shape "square" ] [ set shape "square-x" ]

• Repeat the exercise of:

  • set density = 75% and %-similar-wanted = 95%,
  • press setup and go
  • gradually reduce %-similar-wanted

• Is it easier to see the emerging patterns now?

Another Heuristic

• When you’re at an interesting value for one parameter
  • (e.g., %-similar-wanted = 75%),
  • vary other paremters (density).
  • Set density to 75% and %-similar-wanted to 75%.
    • Vary density
  • Set density to 96% and %-similar-wanted to 75%.
    • Vary %-similar-wanted
    • Set %-similar-wanted to 70%.