#region License Information
/* HeuristicLab
* Copyright (C) 2002-2014 Heuristic and Evolutionary Algorithms Laboratory (HEAL)
*
* This file is part of HeuristicLab.
*
* HeuristicLab is free software: you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation, either version 3 of the License, or
* (at your option) any later version.
*
* HeuristicLab is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with HeuristicLab. If not, see .
*/
#endregion
using System;
using HeuristicLab.Common;
using HeuristicLab.Core;
using HeuristicLab.Data;
using HeuristicLab.Parameters;
using HeuristicLab.Persistence.Default.CompositeSerializers.Storable;
namespace HeuristicLab.Encodings.RealVectorEncoding {
///
/// Blend alpha crossover for real vectors (BLX-a). Creates a new offspring by selecting a random value
/// from the interval between the two alleles of the parent solutions. The interval is increased
/// in both directions by the factor alpha.
///
///
/// 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.
/// The default value for alpha is 0.5.
///
[Item("BlendAlphaCrossover", "The blend alpha crossover (BLX-a) for real vectors creates new offspring by sampling a new value in the range [min_i - d * alpha, max_i + d * alpha) at each position i. Here min_i and max_i are the smaller and larger value of the two parents at position i and d is max_i - min_i. 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.")]
[StorableClass]
public class BlendAlphaCrossover : RealVectorCrossover {
///
/// The alpha parameter specifies how much the interval between the parents should be extended to the left and right.
/// The value of this parameter also determines the name of the operator: BLX-0.0 for example means alpha is set to 0.
/// When Alpha is 0, then the offspring will only be chosen in between the parents, the bigger alpha is the more it will be possible to choose
/// values left and right of the min and max value for each gene.
///
public ValueLookupParameter AlphaParameter {
get { return (ValueLookupParameter)Parameters["Alpha"]; }
}
[StorableConstructor]
protected BlendAlphaCrossover(bool deserializing) : base(deserializing) { }
protected BlendAlphaCrossover(BlendAlphaCrossover original, Cloner cloner) : base(original, cloner) { }
///
/// Initializes a new instance of with one parameter (Alpha).
///
public BlendAlphaCrossover()
: base() {
Parameters.Add(new ValueLookupParameter("Alpha", "The Alpha parameter controls the extension of the range beyond the two parents. It must be >= 0. A value of 0.5 means that half the range is added to both sides of the intervals.", new DoubleValue(0.5)));
}
public override IDeepCloneable Clone(Cloner cloner) {
return new BlendAlphaCrossover(this, cloner);
}
///
/// Performs the blend alpha crossover (BLX-a) of two real vectors.
/// It creates new offspring by sampling a new value in the range [min_i - d * alpha, max_i + d * alpha) at each position i.
/// Here min_i and max_i are the smaller and larger value of the two parents at position i and d is max_i - min_i.
///
///
/// Thrown when and are of different length or
/// when is less than 0.
///
/// The random number generator.
/// The first parent for the crossover operation.
/// The second parent for the crossover operation.
/// The alpha value for the crossover.
/// The newly created real vector resulting from the crossover operation.
public static RealVector Apply(IRandom random, RealVector parent1, RealVector parent2, DoubleValue alpha) {
if (parent1.Length != parent2.Length) throw new ArgumentException("BlendAlphaCrossover: The parents' vectors are of different length.", "parent1");
if (alpha.Value < 0) throw new ArgumentException("BlendAlphaCrossover: Paramter alpha must be greater or equal than 0.", "alpha");
int length = parent1.Length;
RealVector result = new RealVector(length);
double max = 0, min = 0, d = 0, resMin = 0, resMax = 0;
for (int i = 0; i < length; i++) {
max = Math.Max(parent1[i], parent2[i]);
min = Math.Min(parent1[i], parent2[i]);
d = Math.Abs(max - min);
resMin = min - d * alpha.Value;
resMax = max + d * alpha.Value;
result[i] = resMin + random.NextDouble() * Math.Abs(resMax - resMin);
}
return result;
}
///
/// Checks that the number of parents is equal to 2 and forwards the call to .
///
/// Thrown when the number of parents is not equal to 2.
/// Thrown when the parameter alpha could not be found.
/// The random number generator to use.
/// The collection of parents (must be of size 2).
/// The real vector resulting from the crossover operation.
protected override RealVector Cross(IRandom random, ItemArray parents) {
if (parents.Length != 2) throw new ArgumentException("BlendAlphaCrossover: The number of parents is not equal to 2", "parents");
if (AlphaParameter.ActualValue == null) throw new InvalidOperationException("BlendAlphaCrossover: Parameter " + AlphaParameter.ActualName + " could not be found.");
return Apply(random, parents[0], parents[1], AlphaParameter.ActualValue);
}
}
}