Spatial Coordination Game

;;created by Ben Davies
;;for more information, see https://simulatingcomplexity.wordpress.com/2015/06/15/spatially-explicit-iterated-games-in-netlogo-an-agent-based-ht-to-john-nash/

globals [ decisions ]

turtles-own [ cooperate-history defect-history ]

;;setup simulation with

to setup
  clear-all
  ;;seed the decision history to even cooperation and defections for plotting purposes
  set decisions [0 0 0 0 0 1 1 1 1 1]
  ;;create 100 agents, distribute them randomly
  crt 100 [
    setxy random-xcor random-ycor
    set cooperate-history []
    set defect-history []
    ;;set their histories of cooperation and defection to random outcomes of those decisions
    repeat 10 [
      set cooperate-history lput (one-of (list lone-cooperator cooperate-cooperate )) cooperate-history
      set defect-history lput (one-of (list lone-defector defect-defect )) defect-history
    ]
    
  ]
  reset-ticks
end 

to go
  ;;if strategy reaches fixation, stop
  if ((count turtles with [ sum cooperate-history > sum defect-history ])  / count turtles = one-of [ 0 1 ]) [ stop ]
  ;;if model reaches 5000 ticks, stop
  if ticks = 5000 [ stop ]
  ;;clear the decision history for this step
  set decisions []
  ;;move agents according to random walk, then if there are any agents nearby, play a game
  ask turtles [
    set heading random 360
    fd 1
    if any? other turtles in-radius search-radius [
      check-game
    ]
  ]
  tick
end 

to check-game
  
  ;;choices: 0 is defect, 1 is cooperate
  ;;agents choose their strategy based on past experience
  ;;determined by the sum outcomes of their previous experiences
  
   let p1choice 0

   
   ifelse sum cooperate-history > sum defect-history [
     set p1choice 1
   ]
   [
     ifelse sum cooperate-history = sum defect-history [
       set p1choice one-of [ 0 1 ]
     ]
     [
       set p1choice 0
     ]
   ]
    
    
    let p2 one-of other turtles in-radius search-radius
    let p2choice 0

    
   ifelse [ sum cooperate-history ] of p2 > [ sum defect-history ] of p2 [
     set p2choice 1
   ]
   [
     ifelse [ sum cooperate-history ] of p2 = [ sum defect-history ] of p2 [
       set p2choice one-of [ 0 1 ]
     ]
     [
       set p2choice 0
     ]
     
   ]
    
    ifelse p1choice = 1 [ 
      ;;Both cooperate
      ifelse p2choice = 1 [
        set cooperate-history lput cooperate-cooperate cooperate-history
        ask p2 [
          set cooperate-history lput cooperate-cooperate cooperate-history
        ]
      ]
      ;;Player 1 cooperates, Player 2 defects
      [
         set cooperate-history lput lone-cooperator cooperate-history
         ask p2 [
           set defect-history lput lone-defector defect-history
         ]
      ]
    ]
    [
      ;;Player 1 defects, Player 2 cooperates
      ifelse p2choice = 1 [
        set defect-history lput lone-defector defect-history
        ask p2 [
          set cooperate-history lput lone-cooperator cooperate-history
          
        ]
      ]
      ;;Both defect
      [
         set defect-history lput defect-defect defect-history
         ask p2 [
           set defect-history lput defect-defect defect-history
           
         ]
      ]
    ]
    
   ;;drop the oldest memory 
    if length cooperate-history > 10 [
      set cooperate-history remove-item 0 cooperate-history
    ]
    if length defect-history > 10 [
      set defect-history remove-item 0 defect-history
    ]
    ask p2 [
         if length cooperate-history > 10 [
           set cooperate-history remove-item 0 cooperate-history
         ]
         if length defect-history > 10 [
           set defect-history remove-item 0 defect-history
         ]
    ]
    
    ;;record the decisions for plotting
    set decisions lput p1choice decisions
    set decisions lput p2choice decisions
end