Contact Hypothesis Model

globals [
]

breed [ group-a-members group-a-member ]
breed [ group-b-members group-b-member ]

group-a-members-own [ crossing-allowed? prejudice ]
group-b-members-own [ crossing-allowed? prejudice ]

to setup
  clear-all

  ; Draw the horizontal line
  ask patches with [pycor = 0] [ set pcolor green ]

  create-group-a-members group-a-size [
    set color gray
    set shape "person"
    set size 1.5
    set crossing-allowed? (random-float 1 <= percentage-a-cross)
    set prejudice 1 + random 10
    setxy random-xcor (min-pycor + 1 + random (abs 0 - min-pycor - 1))
  ]
  create-group-b-members group-b-size [
    set color orange
    set shape "person"
    set size 1.5
    set crossing-allowed? (random-float 1 <= percentage-b-cross)
    set prejudice 1 + random 10
    setxy random-xcor (1 + random (abs max-pycor - 1))
  ]
  reset-ticks
end 

to update-plot [mean-prejudice-a mean-prejudice-b]
  set-current-plot "Mean Prejudice Levels"
  set-current-plot-pen "group-a"
  plot mean-prejudice-a

  set-current-plot-pen "group-b"
  plot mean-prejudice-b
end 

to go
  ask turtles [
    move
    interact
  ]

  let mean-prejudice-a mean [prejudice] of group-a-members
  let mean-prejudice-b mean [prejudice] of group-b-members

  update-plot mean-prejudice-a mean-prejudice-b

  tick
end 

to move
  let old-xcor xcor
  let old-ycor ycor

  rt random 50 - 25
  if can-move? 1 [
    fd 1
  ]

  ifelse breed = group-a-members [
    if ycor >= 0 and not crossing-allowed? [
      setxy old-xcor old-ycor
    ]
  ] [
    if ycor <= 0 and not crossing-allowed? [
      setxy old-xcor old-ycor
    ]
  ]
end 

to interact
  let other-turtle one-of other turtles-here
  if other-turtle != nobody [
    ifelse breed = group-a-members [
      if [breed] of other-turtle = group-b-members [
        if prejudice < interaction-threshold [
          set prejudice prejudice - (prejudice * prejudice-reduction-factor)
          ask other-turtle [ set prejudice prejudice - (prejudice * prejudice-reduction-factor) ]
        ]
      ]
    ] [
      if [breed] of other-turtle = group-a-members [
        if prejudice < interaction-threshold [
          set prejudice prejudice - (prejudice * prejudice-reduction-factor)
          ask other-turtle [ set prejudice prejudice - (prejudice * prejudice-reduction-factor) ]
        ]
      ]
    ]
  ]
end