Class: Operator::CrossoverTwoPoints

Inherits:
Object
  • Object
show all
Defined in:
../lib/crossover_twopoints.rb

Overview

Classic two-point crossover. It assumes two parents has the form of Arrays. First, the cutting points in both parents are randomly selected, then the middle parts are swapped, forming two new offsprings.

Note the valid cutting point can be placed before the first element or after the last element of the array.

Instance Attribute Summary (collapse)

Instance Method Summary (collapse)

Constructor Details

- (CrossoverTwoPoints) initialize

Create a new two-point crossover operator. 



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# File '../lib/crossover_twopoints.rb', line 13

def initialize
  @random = Kernel
end

Instance Attribute Details

- (Object) random

The source of randomness, used for calling “random.rand( limit )”, defaulting to ‘Kernel’ class. 



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# File '../lib/crossover_twopoints.rb', line 18

def random
  @random
end

Instance Method Details

- (Object) crossover(parent1, parent2, dummy1 = nil, dummy2 = nil)

Take parent1, parent2 arguments and produce [offspring1, offspring2]. For instance: 


  parent1 = [ 1,  2,  3,  4,  5,  6,  7,  8,  9,  10 ]
  parent2 = [ 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23 ]
  xover = CrossoverTwoPoints.new

now producing the offsprings: 


  offspring1, offspring2 = xover.crossover( parent1, parent2 )

offspring1 is [ 1, 2, 3, 4, 5, 16, 17, 18, 8, 9, 10 ] offspring2 is [ 11, 12, 13, 14, 6, 7, 15, 19, 20, 21, 22, 23 ]

This is a stochastic process, thus repeating: 


  offspring1, offspring2 = xover.crossover( parent1, parent2 )

produces: offspring1 is [ 1, 2, 20 ] offspring2 is [ 11, 12, 13, 14, 15, 16, 17, 18, 19, 3, 4, 5, 6, 7, 8, 9, 10, 21, 22, 23 ] 



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# File '../lib/crossover_twopoints.rb', line 38

def crossover( parent1, parent2, dummy1=nil, dummy2=nil )

  return parent1.clone, parent2.clone if parent1.empty? or parent2.empty?
    
  pt11 = @random.rand(parent1.size+1)
  pt12 = @random.rand(parent1.size+1)     
  pt11,pt12 = [pt12,pt11] if pt11 > pt12

  pt21 = @random.rand(parent2.size+1)
  pt22 = @random.rand(parent2.size+1)     
  pt21,pt22 = [pt22,pt21] if pt21 > pt22   

  offs1 = parent1[0...pt11].clone
  offs1 = offs1.concat parent2[pt21...pt22]
  offs1 = offs1.concat parent1[pt12...parent1.size]

  offs2 = parent2[0...pt21].clone
  offs2 = offs2.concat parent1[pt11...pt12]
  offs2 = offs2.concat parent2[pt22...parent2.size]

  return offs1, offs2
 
end