Introduction to Complex Systems

Prof. Dirk Brockmann, Winter Term 2021

Practical Problem 4: Percolation

In this example we will implement a simulation for the process of percolation, see for example the Explorable Barista's Secret

All we need to do is use patches as agents in netlogo.

To do:

  • write a netlogo program in which all patches can have one of three states: "empty", "coffee" and "water"
  • make the world 64x64 in size
  • the setup function should initialize all the patches in the following way
    1. patches should either be empty (white) or coffee (brown).
    2. With a probability P they should be empty
    3. A small disk of patches in the middle should all be water (blue). You can filter the patches according to their x and y coordinates. Check the manual for the variables that store these values.
    4. The probability P should be adjustable with a slider
  • define an "anmalen" function that colors the patches accordingly
  • The go function should carry out the following algorithm
    1. every water patch should turn all the neighboring empty patches into water.
    2. you can have use a construct like this

ask patches with [state = "water"] [
    ask neighbors with [state = "empty"][


  • Using this simulation, try to find the critical concentration of white patches necessary for the water to reach the boundaries of the system.