001/*
002 * Java Genetic Algorithm Library (jenetics-8.1.0).
003 * Copyright (c) 2007-2024 Franz Wilhelmstötter
004 *
005 * Licensed under the Apache License, Version 2.0 (the "License");
006 * you may not use this file except in compliance with the License.
007 * 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 *
017 * Author:
018 *    Franz Wilhelmstötter (franz.wilhelmstoetter@gmail.com)
019 */
020package io.jenetics.ext;
021
022import java.util.random.RandomGenerator;
023
024import io.jenetics.AbstractAlterer;
025import io.jenetics.Chromosome;
026import io.jenetics.Gene;
027import io.jenetics.Mutator;
028import io.jenetics.MutatorResult;
029import io.jenetics.internal.math.Subsets;
030import io.jenetics.util.MSeq;
031
032/**
033 * The reverse sequence mutation, two positions i and j are randomly chosen The
034 * gene order in a chromosome will then be reversed between this two points.
035 * This mutation operator can also be used for combinatorial problems, where no
036 * duplicated genes within a chromosome are allowed, e.g., for the TSP.
037 *
038 * @see io.jenetics.SwapMutator
039 *
040 * @author <a href="mailto:franz.wilhelmstoetter@gmail.com">Franz Wilhelmstötter</a>
041 * @version 5.0
042 * @since 5.0
043 */
044public class RSMutator<
045        G extends Gene<?, G>,
046        C extends Comparable<? super C>
047>
048        extends Mutator<G, C>
049{
050
051        /**
052         * Constructs an alterer with a given recombination probability.
053         *
054         * @param probability the crossover probability.
055         * @throws IllegalArgumentException if the {@code probability} is not in the
056         *          valid range of {@code [0, 1]}.
057         */
058        public RSMutator(final double probability) {
059                super(probability);
060        }
061
062        /**
063         * Default constructor, with default mutation probability
064         * ({@link AbstractAlterer#DEFAULT_ALTER_PROBABILITY}).
065         */
066        public RSMutator() {
067                this(DEFAULT_ALTER_PROBABILITY);
068        }
069
070        @Override
071        protected MutatorResult<Chromosome<G>> mutate(
072                final Chromosome<G> chromosome,
073                final double p,
074                final RandomGenerator random
075        ) {
076                final MutatorResult<Chromosome<G>> result;
077                if (chromosome.length() > 1) {
078                        final int[] points = Subsets.next(random, chromosome.length() + 1, 2);
079                        final MSeq<G> genes = MSeq.of(chromosome);
080                        genes.subSeq(points[0], points[1]).reverse();
081
082                        result = new MutatorResult<>(
083                                chromosome.newInstance(genes.toISeq()),
084                                points[1] - points[0] - 1
085                        );
086                } else {
087                        result = new MutatorResult<>(chromosome, 0);
088                }
089
090                return result;
091        }
092
093}