Ehrenfest Urn Model

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Do Trong Thanh (Author)

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;;;;;;;;;;;;;;;;;;;;;;
;; setup procedures ;;
;;;;;;;;;;;;;;;;;;;;;;

globals
[
  prob
  ratio ;; ratio between number of balls in urn A and total number of balls
  urnA ;; number of balls in urn A
  sum-ratio
  sum-ratio-square
  mean-ratio
  mean-ratio-square
  var
]

;; sets up the patches and creates turtles

to setup
  clear-all
  ask patches [ set pcolor gray + 3 ]
  
  crt 1
  [
    set color black
    set shape "dot"
    set pen-size 3
    setxy 0 0
    set heading 0
    pd
    forward 50
    die
  ]
  init-vars
  setup-turtles
  reset-ticks
end 

to init-vars
  set ratio (ratio-two-urns / (1 + ratio-two-urns))
  set urnA (number-of-particles * ratio)
  set sum-ratio 0
  set sum-ratio-square 0
end 

;; determines the number of turtles and their color

to setup-turtles
  create-turtles urnA
  [
    set size 2
    set shape "dot"
    set ycor (random-float 50)
    set xcor (- (random-float 24)) - 1
    set color blue
  ]
  create-turtles (number-of-particles - urnA)
  [
    set size 2
    set shape "dot"
    set ycor (random-float 50)
    set xcor (random-float 24) + 1
    set color red
  ]
end 

;;;;;;;;;;;;;;;;;;;;;;;;
;; runtime procedures ;;
;;;;;;;;;;;;;;;;;;;;;;;;

to go
  ask one-of turtles
  [
     ifelse (color = blue)
     [
       set color red
       set xcor (random-float 24) + 1
     ]
     [ 
       set color blue
       set xcor (- (random-float 24)) - 1
     ]
  ]
  set urnA (count turtles with [color = blue])
  set ratio (urnA / number-of-particles)
  tick
end

There is only one version of this model, created almost 12 years ago by Do Trong Thanh.

Attached files

File	Type	Description	Last updated
Ehrenfest Urn Model.png	preview	Preview for 'Ehrenfest Urn Model'	almost 12 years ago, by Do Trong Thanh	Download

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