Emergence example: pedestrian flows

globals [changes]

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to setup
  ca
  ask patches [
    ifelse pycor mod 2 = 0 [set pcolor 8] [set pcolor 9]
  ]
  ask n-of n-agents patches [
    sprout 1 [
      set shape "person"
      set size 1.2
      ifelse random 2 = 0 [set heading 90 set color blue] [set heading 270 set color red]
    ]
  ]
  reset-ticks
end 

to go
  set changes 0
  move
  tick
  if ticks > 5000 [stop]
end 

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to move
  ask turtles [
    ifelse any? other turtles-on patch-ahead 1
      [
        ifelse random 2 = 0
          [if ycor < max-pycor [if not any? turtles-on patch xcor (ycor + 1) [set ycor ycor + 1 set changes changes + 1]]]
          [if ycor > min-pycor [if not any? turtles-on patch xcor (ycor - 1) [set ycor ycor - 1 set changes changes + 1]]]
      ]
      [
        fd 1
      ]
  ]
end