| /* |
| * Licensed to the Apache Software Foundation (ASF) under one or more |
| * contributor license agreements. See the NOTICE file distributed with |
| * this work for additional information regarding copyright ownership. |
| * The ASF licenses this file to You 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.apache.commons.math.genetics; |
| |
| import java.util.ArrayList; |
| import java.util.List; |
| |
| |
| /** |
| * One point crossover policy. A random crossover point is selected and the |
| * first part from each parent is copied to the corresponding child, and the |
| * second parts are copied crosswise. |
| * |
| * Example: |
| * <pre> |
| * -C- denotes a crossover point |
| * -C- -C- |
| * p1 = (1 0 1 0 0 1 | 0 1 1) X p2 = (0 1 1 0 1 0 | 1 1 1) |
| * \------------/ \-----/ \------------/ \-----/ |
| * || (*) || (**) |
| * VV (**) VV (*) |
| * /------------\ /-----\ /------------\ /-----\ |
| * c1 = (1 0 1 0 0 1 | 1 1 1) X p2 = (0 1 1 0 1 0 | 0 1 1) |
| * </pre> |
| * |
| * This policy works only on {@link AbstractListChromosome}, and therefore it |
| * is parametrized by T. Moreover, the chromosomes must have same lengths. |
| * |
| * @param <T> generic type of the {@link AbstractListChromosome}s for crossover |
| * @since 2.0 |
| * @version $Revision: 903046 $ $Date: 2010-01-26 03:07:26 +0100 (mar. 26 janv. 2010) $ |
| * |
| */ |
| public class OnePointCrossover<T> implements CrossoverPolicy { |
| |
| /** |
| * Performs one point crossover. A random crossover point is selected and the |
| * first part from each parent is copied to the corresponding child, and the |
| * second parts are copied crosswise. |
| * |
| * Example: |
| * -C- denotes a crossover point |
| * -C- -C- |
| * p1 = (1 0 1 0 0 1 | 0 1 1) X p2 = (0 1 1 0 1 0 | 1 1 1) |
| * \------------/ \-----/ \------------/ \-----/ |
| * || (*) || (**) |
| * VV (**) VV (*) |
| * /------------\ /-----\ /------------\ /-----\ |
| * c1 = (1 0 1 0 0 1 | 1 1 1) X p2 = (0 1 1 0 1 0 | 0 1 1) |
| * |
| * @param first first parent (p1) |
| * @param second second parent (p2) |
| * @return pair of two children (c1,c2) |
| */ |
| @SuppressWarnings("unchecked") // OK because of instanceof checks |
| public ChromosomePair crossover(Chromosome first, Chromosome second) { |
| if (! (first instanceof AbstractListChromosome<?> && second instanceof AbstractListChromosome<?>)) { |
| throw new IllegalArgumentException("One point crossover works on FixedLengthChromosomes only."); |
| } |
| return crossover((AbstractListChromosome<T>) first, (AbstractListChromosome<T>) second); |
| } |
| |
| |
| /** |
| * Helper for {@link #crossover(Chromosome, Chromosome)}. Performs the actual crossover. |
| * |
| * @param first the first chromosome. |
| * @param second the second chromosome. |
| * @return the pair of new chromosomes that resulted from the crossover. |
| */ |
| private ChromosomePair crossover(AbstractListChromosome<T> first, AbstractListChromosome<T> second) { |
| int length = first.getLength(); |
| if (length != second.getLength()) |
| throw new IllegalArgumentException("Both chromosomes must have same lengths."); |
| |
| // array representations of the parents |
| List<T> parent1Rep = first.getRepresentation(); |
| List<T> parent2Rep = second.getRepresentation(); |
| // and of the children |
| ArrayList<T> child1Rep = new ArrayList<T> (first.getLength()); |
| ArrayList<T> child2Rep = new ArrayList<T> (second.getLength()); |
| |
| // select a crossover point at random (0 and length makes no sense) |
| int crossoverIndex = 1 + (GeneticAlgorithm.getRandomGenerator().nextInt(length-2)); |
| |
| // copy the first part |
| for (int i = 0; i < crossoverIndex; i++) { |
| child1Rep.add(parent1Rep.get(i)); |
| child2Rep.add(parent2Rep.get(i)); |
| } |
| // and switch the second part |
| for (int i = crossoverIndex; i < length; i++) { |
| child1Rep.add(parent2Rep.get(i)); |
| child2Rep.add(parent1Rep.get(i)); |
| } |
| |
| return new ChromosomePair( |
| first.newFixedLengthChromosome(child1Rep), |
| second.newFixedLengthChromosome(child2Rep) |
| ); |
| } |
| |
| } |