# Introduction to Complex Systems

Prof. Dirk Brockmann, Winter Term 2021

# Practical Problem 6: Diffusion Limited Aggregation

Create a simulation in which $N=1000$ (you can have a slider for $N$) turtles shaped like circles move around randomly in the netlogo world. Make sure you have sliders for speed and wiggle, like in the other simulations.

All the patches should be made white except for the central patch which should be red, or some other color. Make sure you make you world large enough, e.g. 64x64 patches. You can do this in the settings menu.

When turtles are on a patch that has a red neighbor, the patch with the turtle should turn red. You can get access to the patch on which a turtle is with the command patch-here.

So for example if you are in a turtle you you can test if neighboring patches are red by the command:

if any? neighbors with [ pcolor = red ]

and you can set the patch that the turtle sits on to red by

ask patch-here [ set pcolor red ]

The turtle then should die and a new turtle should be born somewhere on a circle (centered at the origin) with a radius of half the size of the world. Tip: you can create the turtle in the center of the world and just use the command fd RADIUS where RADIUS is half the size of the world. Because when created turtles have a random heading, this should do the job.