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 *      http://www.apache.org/licenses/LICENSE-2.0
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package org.apache.commons.math3.genetics;

import java.util.ArrayList;
import java.util.List;

import org.apache.commons.math3.exception.MathIllegalArgumentException;
import org.apache.commons.math3.exception.util.LocalizedFormats;

Tournament selection scheme. Each of the two selected chromosomes is selected based on n-ary tournament -- this is done by drawing arity random chromosomes without replacement from the population, and then selecting the fittest chromosome among them.
Since:2.0
/** * Tournament selection scheme. Each of the two selected chromosomes is selected * based on n-ary tournament -- this is done by drawing {@link #arity} random * chromosomes without replacement from the population, and then selecting the * fittest chromosome among them. * * @since 2.0 */
public class TournamentSelection implements SelectionPolicy {
number of chromosomes included in the tournament selections
/** number of chromosomes included in the tournament selections */
private int arity;
Creates a new TournamentSelection instance.
Params:
  • arity – how many chromosomes will be drawn to the tournament
/** * Creates a new TournamentSelection instance. * * @param arity how many chromosomes will be drawn to the tournament */
public TournamentSelection(final int arity) { this.arity = arity; }
Select two chromosomes from the population. Each of the two selected chromosomes is selected based on n-ary tournament -- this is done by drawing arity random chromosomes without replacement from the population, and then selecting the fittest chromosome among them.
Params:
  • population – the population from which the chromosomes are chosen.
Throws:
Returns:the selected chromosomes.
/** * Select two chromosomes from the population. Each of the two selected * chromosomes is selected based on n-ary tournament -- this is done by * drawing {@link #arity} random chromosomes without replacement from the * population, and then selecting the fittest chromosome among them. * * @param population the population from which the chromosomes are chosen. * @return the selected chromosomes. * @throws MathIllegalArgumentException if the tournament arity is bigger than the population size */
public ChromosomePair select(final Population population) throws MathIllegalArgumentException { return new ChromosomePair(tournament((ListPopulation) population), tournament((ListPopulation) population)); }
Helper for select(Population). Draw arity random chromosomes without replacement from the population, and then select the fittest chromosome among them.
Params:
  • population – the population from which the chromosomes are chosen.
Throws:
Returns:the selected chromosome.
/** * Helper for {@link #select(Population)}. Draw {@link #arity} random chromosomes without replacement from the * population, and then select the fittest chromosome among them. * * @param population the population from which the chromosomes are chosen. * @return the selected chromosome. * @throws MathIllegalArgumentException if the tournament arity is bigger than the population size */
private Chromosome tournament(final ListPopulation population) throws MathIllegalArgumentException { if (population.getPopulationSize() < this.arity) { throw new MathIllegalArgumentException(LocalizedFormats.TOO_LARGE_TOURNAMENT_ARITY, arity, population.getPopulationSize()); } // auxiliary population ListPopulation tournamentPopulation = new ListPopulation(this.arity) {
{@inheritDoc}
/** {@inheritDoc} */
public Population nextGeneration() { // not useful here return null; } }; // create a copy of the chromosome list List<Chromosome> chromosomes = new ArrayList<Chromosome> (population.getChromosomes()); for (int i=0; i<this.arity; i++) { // select a random individual and add it to the tournament int rind = GeneticAlgorithm.getRandomGenerator().nextInt(chromosomes.size()); tournamentPopulation.addChromosome(chromosomes.get(rind)); // do not select it again chromosomes.remove(rind); } // the winner takes it all return tournamentPopulation.getFittestChromosome(); }
Gets the arity (number of chromosomes drawn to the tournament).
Returns:arity of the tournament
/** * Gets the arity (number of chromosomes drawn to the tournament). * * @return arity of the tournament */
public int getArity() { return arity; }
Sets the arity (number of chromosomes drawn to the tournament).
Params:
  • arity – arity of the tournament
/** * Sets the arity (number of chromosomes drawn to the tournament). * * @param arity arity of the tournament */
public void setArity(final int arity) { this.arity = arity; } }