1 | #region License Information
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2 | /* HeuristicLab
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3 | * Copyright (C) 2002-2014 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.Common;
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24 | using HeuristicLab.Core;
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25 | using HeuristicLab.Data;
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26 | using HeuristicLab.Parameters;
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27 | using HeuristicLab.Persistence.Default.CompositeSerializers.Storable;
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28 |
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29 | namespace HeuristicLab.Encodings.RealVectorEncoding {
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30 | /// <summary>
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31 | /// Performs the simulated binary crossover (SBX) on a vector of real values such that each position is either crossed contracted or expanded with a certain probability.
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32 | /// The probability distribution is designed such that the children will lie closer to their parents as is the case with the single point binary crossover.
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33 | /// </summary>
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34 | /// <remarks>
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35 | /// It is implemented as described in Deb, K. and Agrawal, R. B. 1995. Simulated binary crossover for continuous search space. Complex Systems, 9, pp. 115-148.
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36 | /// </remarks>
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37 | [Item("SimulatedBinaryCrossover", "The simulated binary crossover (SBX) is implemented as described in Deb, K. and Agrawal, R. B. 1995. Simulated binary crossover for continuous search space. Complex Systems, 9, pp. 115-148.")]
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38 | [StorableClass]
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39 | public class SimulatedBinaryCrossover : RealVectorCrossover {
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40 | /// <summary>
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41 | /// The parameter must be greater or equal than 0. Common values are in the range [0;5] and more often just [2;5].
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42 | /// </summary>
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43 | public ValueLookupParameter<DoubleValue> ContiguityParameter {
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44 | get { return (ValueLookupParameter<DoubleValue>)Parameters["Contiguity"]; }
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45 | }
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46 |
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47 | [StorableConstructor]
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48 | protected SimulatedBinaryCrossover(bool deserializing) : base(deserializing) { }
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49 | protected SimulatedBinaryCrossover(SimulatedBinaryCrossover original, Cloner cloner) : base(original, cloner) { }
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50 | /// <summary>
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51 | /// Initializes a new instance of <see cref="SimulatedBinaryCrossover"/> with one
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52 | /// parameter (<c>Contiguity</c>).
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53 | /// </summary>
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54 | public SimulatedBinaryCrossover()
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55 | : base() {
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56 | Parameters.Add(new ValueLookupParameter<DoubleValue>("Contiguity", "Specifies whether the crossover should produce very different (small value) or very similar (large value) children. Valid values must be greater or equal to 0.", new DoubleValue(2)));
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57 | }
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58 |
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59 | public override IDeepCloneable Clone(Cloner cloner) {
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60 | return new SimulatedBinaryCrossover(this, cloner);
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61 | }
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62 |
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63 | /// <summary>
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64 | /// Performs the simulated binary crossover on a real vector. Each position is crossed with a probability of 50% and if crossed either a contracting crossover or an expanding crossover is performed, again with equal probability.
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65 | /// For more details refer to the paper by Deb and Agrawal.
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66 | /// </summary>
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67 | /// <exception cref="ArgumentException">Thrown when the parents' vectors are of unequal length or when <paramref name="contiguity"/> is smaller than 0.</exception>
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68 | /// <remarks>
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69 | /// The manipulated value is not restricted by the (possibly) specified lower and upper bounds. Use the <see cref="BoundsChecker"/> to correct the values after performing the crossover.
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70 | /// </remarks>
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71 | /// <param name="random">The random number generator to use.</param>
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72 | /// <param name="parent1">The first parent vector.</param>
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73 | /// <param name="parent2">The second parent vector.</param>
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74 | /// <param name="contiguity">The contiguity value that specifies how close a child should be to its parents (larger value means closer). The value must be greater or equal than 0. Typical values are in the range [2;5].</param>
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75 | /// <returns>The vector resulting from the crossover.</returns>
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76 | public static RealVector Apply(IRandom random, RealVector parent1, RealVector parent2, DoubleValue contiguity) {
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77 | if (parent1.Length != parent2.Length) throw new ArgumentException("SimulatedBinaryCrossover: Parents are of unequal length");
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78 | if (contiguity.Value < 0) throw new ArgumentException("SimulatedBinaryCrossover: Contiguity value is smaller than 0", "contiguity");
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79 | int length = parent1.Length;
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80 | RealVector result = new RealVector(length);
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81 | for (int i = 0; i < length; i++) {
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82 | if (length == 1 || random.NextDouble() < 0.5) { // cross this variable
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83 | double u = random.NextDouble();
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84 | double beta = 0;
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85 | if (u < 0.5) { // if u is smaller than 0.5 perform a contracting crossover
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86 | beta = Math.Pow(2 * u, 1.0 / (contiguity.Value + 1));
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87 | } else if (u > 0.5) { // otherwise perform an expanding crossover
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88 | beta = Math.Pow(0.5 / (1.0 - u), 1.0 / (contiguity.Value + 1));
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89 | } else if (u == 0.5)
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90 | beta = 1;
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91 |
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92 | if (random.NextDouble() < 0.5)
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93 | result[i] = ((parent1[i] + parent2[i]) / 2.0) - beta * 0.5 * Math.Abs(parent1[i] - parent2[i]);
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94 | else
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95 | result[i] = ((parent1[i] + parent2[i]) / 2.0) + beta * 0.5 * Math.Abs(parent1[i] - parent2[i]);
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96 | } else result[i] = parent1[i];
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97 | }
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98 | return result;
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99 | }
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100 |
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101 | /// <summary>
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102 | /// Checks number of parents, availability of the parameters and forwards the call to <see cref="Apply(IRandom, RealVector, RealVector, DoubleValue)"/>.
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103 | /// </summary>
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104 | /// <exception cref="ArgumentException">Thrown when there are not exactly 2 parents or when the contiguity parameter could not be found.</exception>
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105 | /// <param name="random">The random number generator.</param>
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106 | /// <param name="parents">The collection of parents (must be of size 2).</param>
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107 | /// <returns>The real vector resulting from the crossover.</returns>
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108 | protected override RealVector Cross(IRandom random, ItemArray<RealVector> parents) {
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109 | if (parents.Length != 2) throw new ArgumentException("SimulatedBinaryCrossover: The number of parents is not equal to 2");
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110 | if (ContiguityParameter.ActualValue == null) throw new InvalidOperationException("SimulatedBinaryCrossover: Parameter " + ContiguityParameter.ActualName + " could not be found.");
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111 | return Apply(random, parents[0], parents[1], ContiguityParameter.ActualValue);
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112 | }
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113 | }
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114 | }
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