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//=============================================================================
// Copyright 2006-2010 Daniel W. Dyer
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
//=============================================================================
package org.uncommons.watchmaker.examples.biomorphs;
import java.util.ArrayList;
import java.util.List;
import java.util.Random;
import org.uncommons.maths.random.Probability;
import org.uncommons.watchmaker.framework.EvolutionaryOperator;
/**
* Mutation operator for biomorphs. Mutates each individual gene
* according to some mutation probability.
* @author Daniel Dyer
*/
public class RandomBiomorphMutation implements EvolutionaryOperator<Biomorph>
{
private final Probability mutationProbability;
/**
* @param mutationProbability The probability that a given gene
* is changed.
*/
public RandomBiomorphMutation(Probability mutationProbability)
{
this.mutationProbability = mutationProbability;
}
/**
* Randomly mutate each selected candidate.
* @param selectedCandidates {@inheritDoc}
* @param rng {@inheritDoc}
* @return {@inheritDoc}
*/
public List<Biomorph> apply(List<Biomorph> selectedCandidates, Random rng)
{
List<Biomorph> mutatedPopulation = new ArrayList<Biomorph>(selectedCandidates.size());
for (Biomorph biomorph : selectedCandidates)
{
mutatedPopulation.add(mutateBiomorph(biomorph, rng));
}
return mutatedPopulation;
}
/**
* Mutates a single biomorph.
* @param biomorph The biomorph to mutate.
* @param rng The source of randomness to use for mutation.
* @return A mutated version of the biomorph.
*/
private Biomorph mutateBiomorph(Biomorph biomorph, Random rng)
{
int[] genes = biomorph.getGenotype();
assert genes.length == Biomorph.GENE_COUNT : "Biomorphs must have " + Biomorph.GENE_COUNT + " genes.";
for (int i = 0; i < Biomorph.GENE_COUNT - 1; i++)
{
if (mutationProbability.nextEvent(rng))
{
boolean increase = rng.nextBoolean();
genes[i] += (increase ? 1 : -1);
if (genes[i] > Biomorph.GENE_MAX)
{
genes[i] = Biomorph.GENE_MIN;
}
else if (genes[i] < Biomorph.GENE_MIN)
{
genes[i] = Biomorph.GENE_MAX;
}
}
}
boolean increase = rng.nextBoolean();
genes[Biomorph.LENGTH_GENE_INDEX] += (increase ? 1 : -1);
if (genes[Biomorph.LENGTH_GENE_INDEX] > Biomorph.LENGTH_GENE_MAX)
{
genes[Biomorph.LENGTH_GENE_INDEX] = Biomorph.LENGTH_GENE_MIN;
}
else if (genes[Biomorph.LENGTH_GENE_INDEX] < Biomorph.LENGTH_GENE_MIN)
{
genes[Biomorph.LENGTH_GENE_INDEX] = Biomorph.LENGTH_GENE_MAX;
}
return new Biomorph(genes);
}
}
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