1 | #region License Information
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2 | /* HeuristicLab
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3 | * Copyright (C) 2002-2010 Heuristic and Evolutionary Algorithms Laboratory (HEAL)
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4 | *
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5 | * This file is part of HeuristicLab.
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6 | *
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7 | * HeuristicLab is free software: you can redistribute it and/or modify
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8 | * it under the terms of the GNU General Public License as published by
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9 | * the Free Software Foundation, either version 3 of the License, or
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10 | * (at your option) any later version.
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11 | *
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12 | * HeuristicLab is distributed in the hope that it will be useful,
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13 | * but WITHOUT ANY WARRANTY; without even the implied warranty of
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14 | * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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15 | * GNU General Public License for more details.
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16 | *
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17 | * You should have received a copy of the GNU General Public License
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18 | * along with HeuristicLab. If not, see <http://www.gnu.org/licenses/>.
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19 | */
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20 | #endregion
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21 |
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22 | using System;
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23 | using HeuristicLab.Core;
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24 | using HeuristicLab.Data;
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25 | using HeuristicLab.Parameters;
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26 | using HeuristicLab.Persistence.Default.CompositeSerializers.Storable;
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27 |
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28 | namespace HeuristicLab.Encodings.RealVector {
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29 | /// <summary>
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30 | /// Blend alpha-beta crossover for real vectors (BLX-a-b). Creates a new offspring by selecting a
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31 | /// random value from the interval between the two alleles of the parent solutions.
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32 | /// The interval is increased in both directions as follows: Into the direction of the 'better'
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33 | /// solution by the factor alpha, into the direction of the 'worse' solution by the factor beta.
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34 | /// </summary>
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35 | /// <remarks>
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36 | /// It is implemented as described in Takahashi, M. and Kita, H. 2001. A crossover operator using independent component analysis for real-coded genetic algorithms Proceedings of the 2001 Congress on Evolutionary Computation, pp. 643-649.<br/>
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37 | /// The default value for alpha is 0.75, the default value for beta is 0.25.
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38 | /// </remarks>
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39 | [Item("BlendAlphaBetaCrossover", "The blend alpha beta crossover (BLX-a-b) for real vectors is similar to the blend alpha crossover (BLX-a), but distinguishes between the better and worse of the parents. The interval from which to choose the new offspring can be extended more around the better parent by specifying a higher alpha value. It is implemented as described in Takahashi, M. and Kita, H. 2001. A crossover operator using independent component analysis for real-coded genetic algorithms Proceedings of the 2001 Congress on Evolutionary Computation, pp. 643-649.")]
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40 | [EmptyStorableClass]
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41 | public class BlendAlphaBetaCrossover : RealVectorCrossover {
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42 | public ValueLookupParameter<BoolData> MaximizationParameter {
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43 | get { return (ValueLookupParameter<BoolData>)Parameters["Maximization"]; }
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44 | }
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45 | public SubScopesLookupParameter<DoubleData> QualityParameter {
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46 | get { return (SubScopesLookupParameter<DoubleData>)Parameters["Quality"]; }
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47 | }
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48 | public ValueLookupParameter<DoubleData> AlphaParameter {
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49 | get { return (ValueLookupParameter<DoubleData>)Parameters["Alpha"]; }
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50 | }
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51 | public ValueLookupParameter<DoubleData> BetaParameter {
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52 | get { return (ValueLookupParameter<DoubleData>)Parameters["Beta"]; }
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53 | }
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54 | /// <summary>
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55 | /// Initializes a new instance of <see cref="BlendAlphaBetaCrossover"/> with four additional parameters
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56 | /// (<c>Maximization</c>, <c>Quality</c>, <c>Alpha</c> and <c>Beta</c>).
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57 | /// </summary>
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58 | public BlendAlphaBetaCrossover()
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59 | : base() {
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60 | Parameters.Add(new ValueLookupParameter<BoolData>("Maximization", "Whether the problem is a maximization problem or not."));
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61 | Parameters.Add(new SubScopesLookupParameter<DoubleData>("Quality", "The quality values of the parents."));
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62 | Parameters.Add(new ValueLookupParameter<DoubleData>("Alpha", "The value for alpha.", new DoubleData(0.75)));
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63 | Parameters.Add(new ValueLookupParameter<DoubleData>("Beta", "The value for beta.", new DoubleData(0.25)));
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64 | }
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65 |
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66 | /// <summary>
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67 | /// Performs the blend alpha beta crossover (BLX-a-b) on two parent vectors.
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68 | /// </summary>
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69 | /// <exception cref="ArgumentException">
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70 | /// Thrown when either:<br/>
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71 | /// <list type="bullet">
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72 | /// <item><description>The length of <paramref name="betterParent"/> and <paramref name="worseParent"/> is not equal.</description></item>
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73 | /// <item><description>The parameter <paramref name="alpha"/> is smaller than 0.</description></item>
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74 | /// <item><description>The parameter <paramref name="beta"/> is smaller than 0.</description></item>
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75 | /// </list>
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76 | /// </exception>
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77 | /// <param name="random">The random number generator to use.</param>
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78 | /// <param name="betterParent">The better of the two parents with regard to their fitness.</param>
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79 | /// <param name="worseParent">The worse of the two parents with regard to their fitness.</param>
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80 | /// <param name="alpha">The parameter alpha.</param>
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81 | /// <param name="beta">The parameter beta.</param>
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82 | /// <returns>The real vector that results from the crossover.</returns>
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83 | public static DoubleArrayData Apply(IRandom random, DoubleArrayData betterParent, DoubleArrayData worseParent, DoubleData alpha, DoubleData beta) {
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84 | if (betterParent.Length != worseParent.Length) throw new ArgumentException("BlendAlphaBetaCrossover: The parents' vectors are of different length.", "betterParent");
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85 | if (alpha.Value < 0) throw new ArgumentException("BlendAlphaBetaCrossover: Parameter alpha must be greater or equal to 0.", "alpha");
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86 | if (beta.Value < 0) throw new ArgumentException("BlendAlphaBetaCrossover: Parameter beta must be greater or equal to 0.", "beta");
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87 | int length = betterParent.Length;
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88 | double min, max, d;
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89 | DoubleArrayData result = new DoubleArrayData(length);
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90 |
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91 | for (int i = 0; i < length; i++) {
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92 | d = Math.Abs(betterParent[i] - worseParent[i]);
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93 | if (betterParent[i] <= worseParent[i]) {
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94 | min = betterParent[i] - d * alpha.Value;
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95 | max = worseParent[i] + d * beta.Value;
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96 | } else {
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97 | min = worseParent[i] - d * beta.Value;
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98 | max = betterParent[i] + d * alpha.Value;
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99 | }
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100 | result[i] = min + random.NextDouble() * (max - min);
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101 | }
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102 | return result;
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103 | }
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104 |
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105 | /// <summary>
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106 | /// Checks if the number of parents is equal to 2, if all parameters are available and forwards the call to <see cref="Apply(IRandom, DoubleArrayData, DoubleArrayData, DoubleData, DoubleData)"/>.
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107 | /// </summary>
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108 | /// <exception cref="ArgumentException">Thrown when the number of parents is not equal to 2.</exception>
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109 | /// <exception cref="InvalidOperationException">
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110 | /// Thrown when either:<br/>
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111 | /// <list type="bullet">
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112 | /// <item><description>Maximization parameter could not be found.</description></item>
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113 | /// <item><description>Quality parameter could not be found or the number of quality values is not equal to the number of parents.</description></item>
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114 | /// <item><description>Alpha parameter could not be found.</description></item>
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115 | /// <item><description>Beta parameter could not be found.</description></item>
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116 | /// </list>
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117 | /// </exception>
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118 | /// <param name="random">The random number generator to use.</param>
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119 | /// <param name="parents">The collection of parents (must be of size 2).</param>
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120 | /// <returns>The real vector that results from the crossover.</returns>
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121 | protected override DoubleArrayData Cross(IRandom random, ItemArray<DoubleArrayData> parents) {
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122 | if (parents.Length != 2) throw new ArgumentException("BlendAlphaBetaCrossover: Number of parents is not equal to 2.", "parents");
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123 | if (MaximizationParameter.ActualValue == null) throw new InvalidOperationException("BlendAlphaBetaCrossover: Parameter " + MaximizationParameter.ActualName + " could not be found.");
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124 | if (QualityParameter.ActualValue == null || QualityParameter.ActualValue.Length != parents.Length) throw new InvalidOperationException("BlendAlphaBetaCrossover: Parameter " + QualityParameter.ActualName + " could not be found, or not in the same quantity as there are parents.");
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125 | if (AlphaParameter.ActualValue == null || BetaParameter.ActualValue == null) throw new InvalidOperationException("BlendAlphaBetaCrossover: Parameter " + AlphaParameter.ActualName + " or paramter " + BetaParameter.ActualName + " could not be found.");
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126 |
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127 | ItemArray<DoubleData> qualities = QualityParameter.ActualValue;
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128 | bool maximization = MaximizationParameter.ActualValue.Value;
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129 | // the better parent
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130 | if (maximization && qualities[0].Value >= qualities[1].Value || !maximization && qualities[0].Value <= qualities[1].Value)
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131 | return Apply(random, parents[0], parents[1], AlphaParameter.ActualValue, BetaParameter.ActualValue);
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132 | else {
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133 | return Apply(random, parents[1], parents[0], AlphaParameter.ActualValue, BetaParameter.ActualValue);
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134 | }
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135 | }
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136 | }
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137 | }
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