/*
* Copyright 2012 Friedrich Große, Paul Seiferth,
* Sebastian Starroske, Yannik Stein
*
* This file is part of MetaHeuristics4Java.
*
* MetaHeuristics4Java 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.
*
* MetaHeuristics4Java 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 MetaHeuristics4Java. If not, see <http://www.gnu.org/licenses/>.
*/
package de.mh4j.solver.genetic.matingselection;
import java.util.ArrayList;
import java.util.Collection;
import java.util.List;
import java.util.Random;
import de.mh4j.solver.genetic.Couple;
import de.mh4j.solver.genetic.Genome;
import de.mh4j.solver.genetic.genepool.GenePool;
import de.mh4j.util.RNGGenerator;
/**
*
* TODO write class description
*
*/
public class StochasticUniversalSamplingSelector<GenericGenomeType extends Genome> implements
MatingSelector<GenericGenomeType> {
private final Random random;
/**
* TODO write javadoc
*/
public StochasticUniversalSamplingSelector() {
random = RNGGenerator.createRandomNumberGenerator();
}
/**
* TODO write javadoc
*/
@Override
public Collection<Couple> select(int numberOfPairs, GenePool<GenericGenomeType> genePool) {
List<Couple> couples = new ArrayList<Couple>(numberOfPairs);
for (int i = 0; i < numberOfPairs; i++) {
couples.add(selectRandomCouple(genePool));
}
return couples;
}
private Couple selectRandomCouple(GenePool<GenericGenomeType> genePool) {
double pointer1 = random.nextDouble();
double pointer2;
if (pointer1 > 0.5) {
pointer2 = pointer1;
pointer1 = 1 - pointer1;
}
else {
pointer2 = 1 - pointer1;
}
long fitnessSum = genePool.getFitnessSum();
double probabilitySum = 0;
Genome parent1 = null;
for (Genome genome : genePool) {
double selectionProbability = (fitnessSum == 0) ? 1 : genome.getFitness() / (double) fitnessSum;
probabilitySum += selectionProbability;
if (parent1 == null && probabilitySum >= pointer1) {
parent1 = genome;
}
else if (probabilitySum >= pointer2) {
return new Couple(parent1, genome);
}
}
throw new IllegalStateException("this should never happen");
}
}