TournamentSelection.java revision dee0849a9704d532af0b550146cbafbaa6ee1d19
1dee0849a9704d532af0b550146cbafbaa6ee1d19Raymond/* 2dee0849a9704d532af0b550146cbafbaa6ee1d19Raymond * Licensed to the Apache Software Foundation (ASF) under one or more 3dee0849a9704d532af0b550146cbafbaa6ee1d19Raymond * contributor license agreements. See the NOTICE file distributed with 4dee0849a9704d532af0b550146cbafbaa6ee1d19Raymond * this work for additional information regarding copyright ownership. 5dee0849a9704d532af0b550146cbafbaa6ee1d19Raymond * The ASF licenses this file to You under the Apache License, Version 2.0 6dee0849a9704d532af0b550146cbafbaa6ee1d19Raymond * (the "License"); you may not use this file except in compliance with 7dee0849a9704d532af0b550146cbafbaa6ee1d19Raymond * the License. You may obtain a copy of the License at 8dee0849a9704d532af0b550146cbafbaa6ee1d19Raymond * 9dee0849a9704d532af0b550146cbafbaa6ee1d19Raymond * http://www.apache.org/licenses/LICENSE-2.0 10dee0849a9704d532af0b550146cbafbaa6ee1d19Raymond * 11dee0849a9704d532af0b550146cbafbaa6ee1d19Raymond * Unless required by applicable law or agreed to in writing, software 12dee0849a9704d532af0b550146cbafbaa6ee1d19Raymond * distributed under the License is distributed on an "AS IS" BASIS, 13dee0849a9704d532af0b550146cbafbaa6ee1d19Raymond * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 14dee0849a9704d532af0b550146cbafbaa6ee1d19Raymond * See the License for the specific language governing permissions and 15dee0849a9704d532af0b550146cbafbaa6ee1d19Raymond * limitations under the License. 16dee0849a9704d532af0b550146cbafbaa6ee1d19Raymond */ 17dee0849a9704d532af0b550146cbafbaa6ee1d19Raymondpackage org.apache.commons.math.genetics; 18dee0849a9704d532af0b550146cbafbaa6ee1d19Raymond 19dee0849a9704d532af0b550146cbafbaa6ee1d19Raymondimport java.util.ArrayList; 20dee0849a9704d532af0b550146cbafbaa6ee1d19Raymondimport java.util.List; 21dee0849a9704d532af0b550146cbafbaa6ee1d19Raymond 22dee0849a9704d532af0b550146cbafbaa6ee1d19Raymond/** 23dee0849a9704d532af0b550146cbafbaa6ee1d19Raymond * Tournament selection scheme. Each of the two selected chromosomes is selected 24dee0849a9704d532af0b550146cbafbaa6ee1d19Raymond * based on n-ary tournament -- this is done by drawing {@link #arity} random 25dee0849a9704d532af0b550146cbafbaa6ee1d19Raymond * chromosomes without replacement from the population, and then selecting the 26dee0849a9704d532af0b550146cbafbaa6ee1d19Raymond * fittest chromosome among them. 27dee0849a9704d532af0b550146cbafbaa6ee1d19Raymond * 28dee0849a9704d532af0b550146cbafbaa6ee1d19Raymond * @since 2.0 29dee0849a9704d532af0b550146cbafbaa6ee1d19Raymond * @version $Revision: 811685 $ $Date: 2009-09-05 19:36:48 +0200 (sam. 05 sept. 2009) $ 30dee0849a9704d532af0b550146cbafbaa6ee1d19Raymond */ 31dee0849a9704d532af0b550146cbafbaa6ee1d19Raymondpublic class TournamentSelection implements SelectionPolicy { 32dee0849a9704d532af0b550146cbafbaa6ee1d19Raymond 33dee0849a9704d532af0b550146cbafbaa6ee1d19Raymond /** number of chromosomes included in the tournament selections */ 34dee0849a9704d532af0b550146cbafbaa6ee1d19Raymond private int arity; 35dee0849a9704d532af0b550146cbafbaa6ee1d19Raymond 36dee0849a9704d532af0b550146cbafbaa6ee1d19Raymond /** 37dee0849a9704d532af0b550146cbafbaa6ee1d19Raymond * Creates a new TournamentSelection instance. 38dee0849a9704d532af0b550146cbafbaa6ee1d19Raymond * 39dee0849a9704d532af0b550146cbafbaa6ee1d19Raymond * @param arity 40dee0849a9704d532af0b550146cbafbaa6ee1d19Raymond * how many chromosomes will be drawn to the tournament 41dee0849a9704d532af0b550146cbafbaa6ee1d19Raymond */ 42dee0849a9704d532af0b550146cbafbaa6ee1d19Raymond public TournamentSelection(int arity) { 43dee0849a9704d532af0b550146cbafbaa6ee1d19Raymond this.arity = arity; 44dee0849a9704d532af0b550146cbafbaa6ee1d19Raymond } 45dee0849a9704d532af0b550146cbafbaa6ee1d19Raymond 46dee0849a9704d532af0b550146cbafbaa6ee1d19Raymond /** 47dee0849a9704d532af0b550146cbafbaa6ee1d19Raymond * Select two chromosomes from the population. Each of the two selected 48dee0849a9704d532af0b550146cbafbaa6ee1d19Raymond * chromosomes is selected based on n-ary tournament -- this is done by 49dee0849a9704d532af0b550146cbafbaa6ee1d19Raymond * drawing {@link #arity} random chromosomes without replacement from the 50dee0849a9704d532af0b550146cbafbaa6ee1d19Raymond * population, and then selecting the fittest chromosome among them. 51dee0849a9704d532af0b550146cbafbaa6ee1d19Raymond * 52dee0849a9704d532af0b550146cbafbaa6ee1d19Raymond * @param population 53dee0849a9704d532af0b550146cbafbaa6ee1d19Raymond * the population from which the chromosomes are choosen. 54dee0849a9704d532af0b550146cbafbaa6ee1d19Raymond * @return the selected chromosomes. 55dee0849a9704d532af0b550146cbafbaa6ee1d19Raymond */ 56dee0849a9704d532af0b550146cbafbaa6ee1d19Raymond public ChromosomePair select(Population population) { 57dee0849a9704d532af0b550146cbafbaa6ee1d19Raymond return new ChromosomePair( 58dee0849a9704d532af0b550146cbafbaa6ee1d19Raymond tournament((ListPopulation) population), 59dee0849a9704d532af0b550146cbafbaa6ee1d19Raymond tournament((ListPopulation)population) 60dee0849a9704d532af0b550146cbafbaa6ee1d19Raymond ); 61dee0849a9704d532af0b550146cbafbaa6ee1d19Raymond } 62dee0849a9704d532af0b550146cbafbaa6ee1d19Raymond 63dee0849a9704d532af0b550146cbafbaa6ee1d19Raymond /** 64dee0849a9704d532af0b550146cbafbaa6ee1d19Raymond * Helper for {@link #select(Population)}. Draw {@link #arity} random 65dee0849a9704d532af0b550146cbafbaa6ee1d19Raymond * chromosomes without replacement from the population, and then select the 66dee0849a9704d532af0b550146cbafbaa6ee1d19Raymond * fittest chromosome among them. 67dee0849a9704d532af0b550146cbafbaa6ee1d19Raymond * 68dee0849a9704d532af0b550146cbafbaa6ee1d19Raymond * @param population 69dee0849a9704d532af0b550146cbafbaa6ee1d19Raymond * the population from which the chromosomes are choosen. 70dee0849a9704d532af0b550146cbafbaa6ee1d19Raymond * @return the selected chromosome. 71dee0849a9704d532af0b550146cbafbaa6ee1d19Raymond */ 72dee0849a9704d532af0b550146cbafbaa6ee1d19Raymond private Chromosome tournament(ListPopulation population) { 73dee0849a9704d532af0b550146cbafbaa6ee1d19Raymond if (population.getPopulationSize() < this.arity) 74dee0849a9704d532af0b550146cbafbaa6ee1d19Raymond throw new IllegalArgumentException("Tournament arity cannot be bigger than population size."); 75dee0849a9704d532af0b550146cbafbaa6ee1d19Raymond // auxiliary population 76dee0849a9704d532af0b550146cbafbaa6ee1d19Raymond ListPopulation tournamentPopulation = new ListPopulation(this.arity) { 77dee0849a9704d532af0b550146cbafbaa6ee1d19Raymond public Population nextGeneration() { 78dee0849a9704d532af0b550146cbafbaa6ee1d19Raymond // not useful here 79dee0849a9704d532af0b550146cbafbaa6ee1d19Raymond return null; 80dee0849a9704d532af0b550146cbafbaa6ee1d19Raymond } 81dee0849a9704d532af0b550146cbafbaa6ee1d19Raymond }; 82dee0849a9704d532af0b550146cbafbaa6ee1d19Raymond 83dee0849a9704d532af0b550146cbafbaa6ee1d19Raymond // create a copy of the chromosome list 84dee0849a9704d532af0b550146cbafbaa6ee1d19Raymond List<Chromosome> chromosomes = new ArrayList<Chromosome> (population.getChromosomes()); 85dee0849a9704d532af0b550146cbafbaa6ee1d19Raymond for (int i=0; i<this.arity; i++) { 86dee0849a9704d532af0b550146cbafbaa6ee1d19Raymond // select a random individual and add it to the tournament 87dee0849a9704d532af0b550146cbafbaa6ee1d19Raymond int rind = GeneticAlgorithm.getRandomGenerator().nextInt(chromosomes.size()); 88dee0849a9704d532af0b550146cbafbaa6ee1d19Raymond tournamentPopulation.addChromosome(chromosomes.get(rind)); 89dee0849a9704d532af0b550146cbafbaa6ee1d19Raymond // do not select it again 90dee0849a9704d532af0b550146cbafbaa6ee1d19Raymond chromosomes.remove(rind); 91dee0849a9704d532af0b550146cbafbaa6ee1d19Raymond } 92dee0849a9704d532af0b550146cbafbaa6ee1d19Raymond // the winner takes it all 93dee0849a9704d532af0b550146cbafbaa6ee1d19Raymond return tournamentPopulation.getFittestChromosome(); 94dee0849a9704d532af0b550146cbafbaa6ee1d19Raymond } 95dee0849a9704d532af0b550146cbafbaa6ee1d19Raymond 96dee0849a9704d532af0b550146cbafbaa6ee1d19Raymond /** 97dee0849a9704d532af0b550146cbafbaa6ee1d19Raymond * Gets the arity (number of chromosomes drawn to the tournament). 98dee0849a9704d532af0b550146cbafbaa6ee1d19Raymond * 99dee0849a9704d532af0b550146cbafbaa6ee1d19Raymond * @return arity of the tournament 100dee0849a9704d532af0b550146cbafbaa6ee1d19Raymond */ 101dee0849a9704d532af0b550146cbafbaa6ee1d19Raymond public int getArity() { 102dee0849a9704d532af0b550146cbafbaa6ee1d19Raymond return arity; 103dee0849a9704d532af0b550146cbafbaa6ee1d19Raymond } 104dee0849a9704d532af0b550146cbafbaa6ee1d19Raymond 105dee0849a9704d532af0b550146cbafbaa6ee1d19Raymond /** 106dee0849a9704d532af0b550146cbafbaa6ee1d19Raymond * Sets the arity (number of chromosomes drawn to the tournament). 107dee0849a9704d532af0b550146cbafbaa6ee1d19Raymond * 108dee0849a9704d532af0b550146cbafbaa6ee1d19Raymond * @param arity arity of the tournament 109dee0849a9704d532af0b550146cbafbaa6ee1d19Raymond */ 110dee0849a9704d532af0b550146cbafbaa6ee1d19Raymond public void setArity(int arity) { 111dee0849a9704d532af0b550146cbafbaa6ee1d19Raymond this.arity = arity; 112dee0849a9704d532af0b550146cbafbaa6ee1d19Raymond } 113dee0849a9704d532af0b550146cbafbaa6ee1d19Raymond 114dee0849a9704d532af0b550146cbafbaa6ee1d19Raymond} 115