;; From the NetLogo Model Library: Social Science - Segregation Model



globals [
  percent-similar  ;; on the average, what percent of a turtle's neighbors
                   ;; are the same color as that turtle?
  percent-unhappy  ;; what percent of the turtles are unhappy?
]



turtles-own [
  happy?       ;; for each turtle, indicates whether at least %-similar-wanted percent of
               ;; that turtles' neighbors are the same color as the turtle
]



patches-own [
  reds-nearby   ;; how many neighboring patches have a red turtle?
  greens-nearby ;; ditto for green turtles
  total-nearby  ;; sum of previous two variables
]



to setup
  ca
  cct number
  [
    setxy (random screen-size-x)  ;; randomize the turtle locations
          (random screen-size-y)
    ifelse who < (number / 2)     ;; turn half the turtles red, the others green
      [ set color red ]
      [ set color green ]
    if any other-turtles-here     ;; make sure each turtle is in its own patch
      [ find-new-spot ]
  ]
  update-variables
  do-plots
end



to go
  move-unhappy-turtles
  update-variables
  do-plots
  if not any turtles with [not happy?] [ stop ]
end



to move-unhappy-turtles
  ask turtles [
    if not happy?
      [ find-new-spot ]
  ]
end



to find-new-spot
  rt random 360
  fd random 10
  if any other-turtles-here
    [ find-new-spot ]          ;; keep going until we find an unoccupied patch
end




to update-variables
  update-patches
  update-turtles
  update-globals
end




to update-patches
  ask patches [
    ;; in next two lines, we use "neighbors" to test the eight patches surrounding
    ;; the current patch
    set reds-nearby count neighbors with [any turtles-here with [color = red]]
    set greens-nearby count neighbors with [any turtles-here with [color = green]]
    set total-nearby reds-nearby + greens-nearby
  ]
end




to update-turtles
  ask turtles [
    if color = red
      [ set happy? reds-nearby >= ( %-similar-wanted * total-nearby / 100 ) ]
    if color = green
      [ set happy? greens-nearby >= ( %-similar-wanted * total-nearby / 100 ) ]
  ]
end



to update-globals
  locals [ similar-neighbors total-neighbors ]
  set similar-neighbors
      sum values-from turtles with [color = red] [reds-nearby] +
      sum values-from turtles with [color = green] [greens-nearby]
  set total-neighbors
      sum values-from turtles [total-nearby]
  set percent-similar (similar-neighbors / total-neighbors) * 100
  set percent-unhappy (count turtles with [not happy?]) / (count turtles) * 100
end



to do-plots
  set-current-plot "Percent Similar"
  plot percent-similar
  set-current-plot "Percent Unhappy"
  plot percent-unhappy
end