OnePointCrossover.java revision dee0849a9704d532af0b550146cbafbaa6ee1d19
1/* 2 * Licensed to the Apache Software Foundation (ASF) under one or more 3 * contributor license agreements. See the NOTICE file distributed with 4 * this work for additional information regarding copyright ownership. 5 * The ASF licenses this file to You under the Apache License, Version 2.0 6 * (the "License"); you may not use this file except in compliance with 7 * the License. You may obtain a copy of the License at 8 * 9 * http://www.apache.org/licenses/LICENSE-2.0 10 * 11 * Unless required by applicable law or agreed to in writing, software 12 * distributed under the License is distributed on an "AS IS" BASIS, 13 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 14 * See the License for the specific language governing permissions and 15 * limitations under the License. 16 */ 17package org.apache.commons.math.genetics; 18 19import java.util.ArrayList; 20import java.util.List; 21 22 23/** 24 * One point crossover policy. A random crossover point is selected and the 25 * first part from each parent is copied to the corresponding child, and the 26 * second parts are copied crosswise. 27 * 28 * Example: 29 * <pre> 30 * -C- denotes a crossover point 31 * -C- -C- 32 * p1 = (1 0 1 0 0 1 | 0 1 1) X p2 = (0 1 1 0 1 0 | 1 1 1) 33 * \------------/ \-----/ \------------/ \-----/ 34 * || (*) || (**) 35 * VV (**) VV (*) 36 * /------------\ /-----\ /------------\ /-----\ 37 * c1 = (1 0 1 0 0 1 | 1 1 1) X p2 = (0 1 1 0 1 0 | 0 1 1) 38 * </pre> 39 * 40 * This policy works only on {@link AbstractListChromosome}, and therefore it 41 * is parametrized by T. Moreover, the chromosomes must have same lengths. 42 * 43 * @param <T> generic type of the {@link AbstractListChromosome}s for crossover 44 * @since 2.0 45 * @version $Revision: 903046 $ $Date: 2010-01-26 03:07:26 +0100 (mar. 26 janv. 2010) $ 46 * 47 */ 48public class OnePointCrossover<T> implements CrossoverPolicy { 49 50 /** 51 * Performs one point crossover. A random crossover point is selected and the 52 * first part from each parent is copied to the corresponding child, and the 53 * second parts are copied crosswise. 54 * 55 * Example: 56 * -C- denotes a crossover point 57 * -C- -C- 58 * p1 = (1 0 1 0 0 1 | 0 1 1) X p2 = (0 1 1 0 1 0 | 1 1 1) 59 * \------------/ \-----/ \------------/ \-----/ 60 * || (*) || (**) 61 * VV (**) VV (*) 62 * /------------\ /-----\ /------------\ /-----\ 63 * c1 = (1 0 1 0 0 1 | 1 1 1) X p2 = (0 1 1 0 1 0 | 0 1 1) 64 * 65 * @param first first parent (p1) 66 * @param second second parent (p2) 67 * @return pair of two children (c1,c2) 68 */ 69 @SuppressWarnings("unchecked") // OK because of instanceof checks 70 public ChromosomePair crossover(Chromosome first, Chromosome second) { 71 if (! (first instanceof AbstractListChromosome<?> && second instanceof AbstractListChromosome<?>)) { 72 throw new IllegalArgumentException("One point crossover works on FixedLengthChromosomes only."); 73 } 74 return crossover((AbstractListChromosome<T>) first, (AbstractListChromosome<T>) second); 75 } 76 77 78 /** 79 * Helper for {@link #crossover(Chromosome, Chromosome)}. Performs the actual crossover. 80 * 81 * @param first the first chromosome. 82 * @param second the second chromosome. 83 * @return the pair of new chromosomes that resulted from the crossover. 84 */ 85 private ChromosomePair crossover(AbstractListChromosome<T> first, AbstractListChromosome<T> second) { 86 int length = first.getLength(); 87 if (length != second.getLength()) 88 throw new IllegalArgumentException("Both chromosomes must have same lengths."); 89 90 // array representations of the parents 91 List<T> parent1Rep = first.getRepresentation(); 92 List<T> parent2Rep = second.getRepresentation(); 93 // and of the children 94 ArrayList<T> child1Rep = new ArrayList<T> (first.getLength()); 95 ArrayList<T> child2Rep = new ArrayList<T> (second.getLength()); 96 97 // select a crossover point at random (0 and length makes no sense) 98 int crossoverIndex = 1 + (GeneticAlgorithm.getRandomGenerator().nextInt(length-2)); 99 100 // copy the first part 101 for (int i = 0; i < crossoverIndex; i++) { 102 child1Rep.add(parent1Rep.get(i)); 103 child2Rep.add(parent2Rep.get(i)); 104 } 105 // and switch the second part 106 for (int i = crossoverIndex; i < length; i++) { 107 child1Rep.add(parent2Rep.get(i)); 108 child2Rep.add(parent1Rep.get(i)); 109 } 110 111 return new ChromosomePair( 112 first.newFixedLengthChromosome(child1Rep), 113 second.newFixedLengthChromosome(child2Rep) 114 ); 115 } 116 117} 118