Simulated Annealing2

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Uri Wilensky (Author)

VERSION

$Id: Simulated Annealing2.nlogo 39709 2008-05-01 17:53:24Z tisue $

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patches-own [ brightness ]

to setup
  ca
  ask patches [
    set brightness random-float 10 ;5 + 10 * random 14 ;random-float 1.0
    update-visual
  ]
end 

to go
  ask patches
  [
    try-change self
  ]
  set temperature temperature * temperature-drop-ratio
  tick
end 

to update-visual
  set pcolor brightness ;  scale-color gray brightness 0 1
end 

to-report accept-change? [ old-fitness new-fitness ]
  report (random-float 100) < temperature or new-fitness > old-fitness
end 

to try-change [ p1 ]
  let p2 one-of ( [neighbors] of p1 )
  let affected-patches (patch-set ([neighbors] of p1) ([neighbors] of p2))
  let old-fitness sum [get-fitness] of affected-patches
  swap-values p1 p2
  let new-fitness sum [get-fitness] of affected-patches
  ifelse (accept-change? old-fitness new-fitness)
  [
    ask p1 [ update-visual ]
    ask p2 [ update-visual ]
  ]
  [
    swap-values p1 p2
  ]
end 

to swap-values [ p1 p2 ]
  let temp [ brightness ] of p1
  ask p1 [ set brightness [brightness] of p2 ]
  ask p2 [ set brightness temp ]    
end 

to-report get-fitness  ; patch-procedure
  let unhappiness 0.0
  ask neighbors [ 
    set unhappiness unhappiness + (brightness - [brightness] of myself) ^ 2
  ]
  report 8 - unhappiness
end

There is only one version of this model, created almost 14 years ago by Uri Wilensky.

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