Class: Operator::CrossoverRipple

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

Overview

Single point GE crossover. It assumes two parents has the form of Arrays. First, the cutting points in both parents are randomly selected, then the parts after these points are swapped, forming two new offsprings.

The positions of possible cutting points can be flexibly configured (which may be important for complex Mappers using more than one genome value per codon). Production of empty offsprings can be allowed or prohibited as well by the crossover’s configuration. The cutting point positions in both parents can be either fixed or independent.

Instance Attribute Summary (collapse)

Instance Method Summary (collapse)

Constructor Details

- (CrossoverRipple) initialize

Create a new crossover facility with the default attribute values. 



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# File '../lib/crossover_ripple.rb', line 16

def initialize
  @random = Kernel
  @margin = 0
  @step = 1
  @fixed = false
  @tolerance = true
end

Instance Attribute Details

- (Object) fixed

Whether the CrossoverRipple uses the same position (Array index) for both parents’ cutting points, defaulting to false. 



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# File '../lib/crossover_ripple.rb', line 34

def fixed
  @fixed
end

- (Object) margin

The minimal number of genome vector values kept from the beginning and ending of the parent vector, defaulting to 0. 



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# File '../lib/crossover_ripple.rb', line 28

def margin
  @margin
end

- (Object) random

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



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# File '../lib/crossover_ripple.rb', line 25

def random
  @random
end

- (Object) step

The number of genome vector values between tho possible cutting points, defaulting to 1. 



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# File '../lib/crossover_ripple.rb', line 31

def step
  @step
end

- (Object) tolerance

Whether the empty array is allowed as the valid offspring (if set to false, the exception is raised), defaulting to true. 



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# File '../lib/crossover_ripple.rb', line 37

def tolerance
  @tolerance
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 = CrossoverRipple.new

possible cutting points with default setting (denoted by ’|’ symbol): 


  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 | ]

after xover.margin = 3, the allowed cutting points are: 


  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 ]

after xover.step = 2, the allowed cutting points are: 


  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 ]

now producing the offsprings: 


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

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

This is stochastic process, thus repeating: 


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

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



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# File '../lib/crossover_ripple.rb', line 70

def crossover( parent1, parent2, dummy1=nil, dummy2=nil )
  pts1 = []
  @margin.step( parent1.size - @margin, @step ) { |i| pts1.push i }
  pts2 = []
  @margin.step( parent2.size - @margin, @step ) { |i| pts2.push i }

  if pts1.empty? or pts2.empty? 
    return parent1.clone, parent2.clone if @tolerance #fallback 
    raise "CrossoverRipple: operand(s) too short"
  end

  if @fixed 
    if parent1.size < parent2.size
      pt1 = pt2 = pts1.at( @random.rand(pts1.size) )
    else
      pt1 = pt2 = pts2.at( @random.rand(pts2.size) )
    end
  else
    pt1 = pts1.at @random.rand(pts1.size)
    pt2 = pts2.at @random.rand(pts2.size)
  end

  offs1 = parent1[0...pt1].clone
  offs1 = offs1.concat parent2[pt2...parent2.size]
  offs2 = parent2[0...pt2].clone   
  offs2 = offs2.concat parent1[pt1...parent1.size]
  return offs1, offs2
end