list_crossover.rb

Path: lib/charlie/list/list_crossover.rb
Last Update: Fri May 09 14:21:11 +0200 2008

Methods

BlendingCrossover   NPointCrossover  

Constants

TwoPointCrossover = NPointCrossover(2)
ThreePointCrossover = NPointCrossover(3)
BlendingCrossover = BlendingCrossover()

Public Instance methods

BlendingCrossover(exploration_alpha=0.1,type=:cube)

Blending crossover, common in evolutionary strategies.

  • Given two parents x1(i), x2(i)
  • Returns two children with as i‘th elements y(i)x1(i)+(1-y(i))x2(i) and y(i)x2(i)+(1-y(i))x1(i)
  • type=:cube takes y(i) independent, so children roughly within the hypercube spanned by the parents.
  • type=:line takes y(i)=y(1), so children roughly on the line between the parents.
  • exploration_alpha defines how far outside the hypercube/line spanned by the parents the children can be. (more specifically, y(i) = (1+2*alpha)*rand - alpha)

[Source]

    # File lib/charlie/list/list_crossover.rb, line 58
58: def BlendingCrossover(exploration_alpha=0.1,type=:cube)
59:   sz_rand = 1 + 2 * exploration_alpha
60:   Module.new{
61:     self.name = "BlendingCrossover(#{exploration_alpha},#{type})"
62:     if(type==:cube) 
63:       define_method(:cross){|parent1,parent2|
64:         c1 = []; c2=[]; g1 = parent1.genes; g2 = parent2.genes
65:         g1.each_with_index{|e,i|
66:           y  = rand*sz_rand - exploration_alpha 
67:           x2 = g2[i]
68:           c1 << y*e  + (1-y)*x2
69:           c2 << y*x2 + (1-y)*e
70:         }
71:         [c1,c2].map{|x| from_genes(x) }
72:       }
73:     elsif(type==:line) 
74:       define_method(:cross){|parent1,parent2|
75:         c1 = []; c2=[]; g1 = parent1.genes; g2 = parent2.genes
76:         y  = rand*sz_rand - exploration_alpha 
77:         g1.each_with_index{|e,i|
78:           x2 = g2[i]
79:           c1 << y*e  + (1-y)*x2
80:           c2 << y*x2 + (1-y)*e
81:         } 
82:         [c1,c2].map{|x| from_genes(x) }
83:       }
84:     else 
85:       raise ArgumentError,"Invalid BlendingCrossover type #{type}"
86:     end
87:   }
88: end
NPointCrossover(n=2)

n point crossover, returns two children.

[Source]

    # File lib/charlie/list/list_crossover.rb, line 14
14: def NPointCrossover(n=2)
15:  Module.new{
16:   self.name = "NPointCrossover(#{n})"
17:   define_method(:cross){|parent1,parent2|
18:     p1 = parent1.genes; p2 = parent2.genes
19:     upper_bnd = p1.size + 1
20:     cross_pts = (0...n).map{rand(upper_bnd)}.sort
21: 
22:     c1 = []; c2=[]
23:     ([0] + cross_pts << upper_bnd).each_cons(2){|cp1,cp2|
24:       c1 += p1[cp1...cp2]
25:       c2 += p2[cp1...cp2]
26:       p1,p2 = p2,p1
27:     }
28:     [c1,c2].map{|x| from_genes(x) }
29:   }
30:  }
31: end

[Validate]