001/*
002 * Licensed to the Apache Software Foundation (ASF) under one or more
003 * contributor license agreements.  See the NOTICE file distributed with
004 * this work for additional information regarding copyright ownership.
005 * The ASF licenses this file to You under the Apache License, Version 2.0
006 * (the "License"); you may not use this file except in compliance with
007 * the License.  You may obtain a copy of the License at
008 *
009 *      http://www.apache.org/licenses/LICENSE-2.0
010 *
011 * Unless required by applicable law or agreed to in writing, software
012 * distributed under the License is distributed on an "AS IS" BASIS,
013 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
014 * See the License for the specific language governing permissions and
015 * limitations under the License.
016 */
017package org.apache.commons.math4.genetics;
018
019import java.util.ArrayList;
020import java.util.List;
021
022import org.apache.commons.math4.exception.MathIllegalArgumentException;
023import org.apache.commons.math4.exception.util.LocalizedFormats;
024
025/**
026 * Mutation for {@link BinaryChromosome}s. Randomly changes one gene.
027 *
028 * @since 2.0
029 */
030public class BinaryMutation implements MutationPolicy {
031
032    /**
033     * Mutate the given chromosome. Randomly changes one gene.
034     *
035     * @param original the original chromosome.
036     * @return the mutated chromosome.
037     * @throws MathIllegalArgumentException if <code>original</code> is not an instance of {@link BinaryChromosome}.
038     */
039    @Override
040    public Chromosome mutate(Chromosome original) throws MathIllegalArgumentException {
041        if (!(original instanceof BinaryChromosome)) {
042            throw new MathIllegalArgumentException(LocalizedFormats.INVALID_BINARY_CHROMOSOME);
043        }
044
045        BinaryChromosome origChrom = (BinaryChromosome) original;
046        List<Integer> newRepr = new ArrayList<>(origChrom.getRepresentation());
047
048        // randomly select a gene
049        int geneIndex = GeneticAlgorithm.getRandomGenerator().nextInt(origChrom.getLength());
050        // and change it
051        newRepr.set(geneIndex, origChrom.getRepresentation().get(geneIndex) == 0 ? 1 : 0);
052
053        Chromosome newChrom = origChrom.newFixedLengthChromosome(newRepr);
054        return newChrom;
055    }
056
057}