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;
021
022import static io.jenetics.internal.math.Randoms.indexes;
023
024import java.util.random.RandomGenerator;
025
026import io.jenetics.util.MSeq;
027
028/**
029 * The {@code SwapMutation} changes the order of genes in a chromosome, with the
030 * hope of bringing related genes closer together, thereby facilitating the
031 * production of building blocks. This mutation operator can also be used for
032 * combinatorial problems, where no duplicated genes within a chromosome are
033 * allowed, e.g., for the TSP.
034 * <p>
035 * This mutator is also known as <em>Partial Shuffle Mutator</em> (PSM).
036 *
037 * @see <a href="https://arxiv.org/ftp/arxiv/papers/1203/1203.3099.pdf">
038 *     Analyzing the Performance of Mutation Operators to Solve the Travelling
039 *     Salesman Problem</a>
040 *
041 * @author <a href="mailto:franz.wilhelmstoetter@gmail.com">Franz Wilhelmstötter</a>
042 * @since 1.0
043 * @version 5.0
044 */
045public class SwapMutator<
046        G extends Gene<?, G>,
047        C extends Comparable<? super C>
048>
049        extends Mutator<G, C>
050{
051
052        /**
053         * Constructs an alterer with a given recombination probability.
054         *
055         * @param probability the crossover probability.
056         * @throws IllegalArgumentException if the {@code probability} is not in the
057         *          valid range of {@code [0, 1]}.
058         */
059        public SwapMutator(final double probability) {
060                super(probability);
061        }
062
063        /**
064         * Default constructor, with default mutation probability
065         * ({@link AbstractAlterer#DEFAULT_ALTER_PROBABILITY}).
066         */
067        public SwapMutator() {
068                this(DEFAULT_ALTER_PROBABILITY);
069        }
070
071        /**
072         * Swaps the genes in the given array, with the mutation probability of this
073         * mutation.
074         */
075        @Override
076        protected MutatorResult<Chromosome<G>> mutate(
077                final Chromosome<G> chromosome,
078                final double p,
079                final RandomGenerator random
080        ) {
081                final MutatorResult<Chromosome<G>> result;
082                if (chromosome.length() > 1) {
083                        final MSeq<G> genes = MSeq.of(chromosome);
084                        final int mutations = (int)indexes(random, genes.length(), p)
085                                .peek(i -> genes.swap(i, random.nextInt(genes.length())))
086                                .count();
087
088                        result = new MutatorResult<>(
089                                chromosome.newInstance(genes.toISeq()),
090                                mutations
091                        );
092                } else {
093                        result = new MutatorResult<>(chromosome, 0);
094                }
095
096                return result;
097        }
098
099}