#region License Information
/* HeuristicLab
* Copyright (C) 2002-2013 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 {
///
/// 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.
/// 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.
///
///
/// 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.
///
[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.")]
[StorableClass]
public class SimulatedBinaryCrossover : RealVectorCrossover {
///
/// The parameter must be greater or equal than 0. Common values are in the range [0;5] and more often just [2;5].
///
public ValueLookupParameter ContiguityParameter {
get { return (ValueLookupParameter)Parameters["Contiguity"]; }
}
[StorableConstructor]
protected SimulatedBinaryCrossover(bool deserializing) : base(deserializing) { }
protected SimulatedBinaryCrossover(SimulatedBinaryCrossover original, Cloner cloner) : base(original, cloner) { }
///
/// Initializes a new instance of with one
/// parameter (Contiguity).
///
public SimulatedBinaryCrossover()
: base() {
Parameters.Add(new ValueLookupParameter("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)));
}
public override IDeepCloneable Clone(Cloner cloner) {
return new SimulatedBinaryCrossover(this, cloner);
}
///
/// 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.
/// For more details refer to the paper by Deb and Agrawal.
///
/// Thrown when the parents' vectors are of unequal length or when is smaller than 0.
///
/// The manipulated value is not restricted by the (possibly) specified lower and upper bounds. Use the to correct the values after performing the crossover.
///
/// The random number generator to use.
/// The first parent vector.
/// The second parent vector.
/// 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].
/// The vector resulting from the crossover.
public static RealVector Apply(IRandom random, RealVector parent1, RealVector parent2, DoubleValue contiguity) {
if (parent1.Length != parent2.Length) throw new ArgumentException("SimulatedBinaryCrossover: Parents are of unequal length");
if (contiguity.Value < 0) throw new ArgumentException("SimulatedBinaryCrossover: Contiguity value is smaller than 0", "contiguity");
int length = parent1.Length;
RealVector result = new RealVector(length);
for (int i = 0; i < length; i++) {
if (length == 1 || random.NextDouble() < 0.5) { // cross this variable
double u = random.NextDouble();
double beta = 0;
if (u < 0.5) { // if u is smaller than 0.5 perform a contracting crossover
beta = Math.Pow(2 * u, 1.0 / (contiguity.Value + 1));
} else if (u > 0.5) { // otherwise perform an expanding crossover
beta = Math.Pow(0.5 / (1.0 - u), 1.0 / (contiguity.Value + 1));
} else if (u == 0.5)
beta = 1;
if (random.NextDouble() < 0.5)
result[i] = ((parent1[i] + parent2[i]) / 2.0) - beta * 0.5 * Math.Abs(parent1[i] - parent2[i]);
else
result[i] = ((parent1[i] + parent2[i]) / 2.0) + beta * 0.5 * Math.Abs(parent1[i] - parent2[i]);
} else result[i] = parent1[i];
}
return result;
}
///
/// Checks number of parents, availability of the parameters and forwards the call to .
///
/// Thrown when there are not exactly 2 parents or when the contiguity parameter could not be found.
/// The random number generator.
/// The collection of parents (must be of size 2).
/// The real vector resulting from the crossover.
protected override RealVector Cross(IRandom random, ItemArray parents) {
if (parents.Length != 2) throw new ArgumentException("SimulatedBinaryCrossover: The number of parents is not equal to 2");
if (ContiguityParameter.ActualValue == null) throw new InvalidOperationException("SimulatedBinaryCrossover: Parameter " + ContiguityParameter.ActualName + " could not be found.");
return Apply(random, parents[0], parents[1], ContiguityParameter.ActualValue);
}
}
}