Class: Wallace::Operators::CycleCrossoverOperator

Inherits:
Wallace::Operator show all
Defined in:
lib/operators/cycle_crossover_operation.rb

Overview

Credit: Oliver, I. M., Smith, D. J., & Holland, J. R. C. (1987). A study of permutation crossover operators on the traveling salesman problem. In Proceedings of the second international conference. on genetic algorithms (ICGA’87) (pp. 224–230). Cambridge, MA:Massachusetts Institute of Technology

Defined Under Namespace

Classes: HashPair

Instance Method Summary collapse

Methods inherited from Wallace::Operator

#initialize, #produce

Constructor Details

This class inherits a constructor from Wallace::Operator

Instance Method Details

#operate(rng, parents) ⇒ Object 



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# File 'lib/operators/cycle_crossover_operation.rb', line 14

def operate(rng, parents)

  # http://www.rubicite.com/Tutorials/GeneticAlgorithms/CrossoverOperators/CycleCrossoverOperator.aspx
  length = parents[0].length
  children = [
    Array.new(length) { nil },
    Array.new(length) { nil }
  ]

  # Generate a hash to indicate when certain indices have been
  # used in a cycle.
  used = Hash[(0...length).map { |v| [v, false] }]

  # REVERSE ENGINEER.
  helper = Hash[(0...length).map { |v|
    temp_pair = HashPair.new(
      parents[0][v],
      parents[1][v],
      v
    )
    [parents[1][v], temp_pair]
  }]

  cycles = []
  (0...length).each do |j|
    cyc = []
    unless used[j] then
      
      cyc_start = j

      temp_pair = helper[parents[0][cyc_start]]
      cyc << temp_pair
      used[temp_pair.i2] = true

      until temp_pair.i2 == cyc_start
        temp_pair = helper[parents[0][temp_pair.i2]]
        cyc << temp_pair
        used[temp_pair.i2] = true
      end

    end
    cycles << cyc
  end

  # Alternating cycles.
  cycles.each_with_index do |cyc, num|
    if (num % 2) == 0
      cyc.each do |temp_pair|
        children[0][temp_pair.i2] = temp_pair.v1
        children[1][temp_pair.i2] = temp_pair.v2
      end
    else
      cyc.each do |temp_pair|
        children[0][temp_pair.i2] = temp_pair.v2
        children[1][temp_pair.i2] = temp_pair.v1
      end
    end
  end

  return children

end