001 /*
002 * Java Genetic Algorithm Library (jenetics-4.0.0).
003 * Copyright (c) 2007-2017 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 */
020 package io.jenetics;
021
022 import static java.lang.String.format;
023 import static io.jenetics.internal.math.random.indexes;
024
025 import java.util.Random;
026
027 import io.jenetics.internal.util.Equality;
028 import io.jenetics.internal.util.Hash;
029 import io.jenetics.util.MSeq;
030
031 /**
032 * The {@code SwapMutation} changes the order of genes in a chromosome, with the
033 * hope of bringing related genes closer together, thereby facilitating the
034 * production of building blocks. This mutation operator can also be used for
035 * combinatorial problems, where no duplicated genes within a chromosome are
036 * allowed, e.g. for the TSP.
037 *
038 * @author <a href="mailto:franz.wilhelmstoetter@gmail.com">Franz Wilhelmstötter</a>
039 * @since 1.0
040 * @version 4.0
041 */
042 public class SwapMutator<
043 G extends Gene<?, G>,
044 C extends Comparable<? super C>
045 >
046 extends Mutator<G, C>
047 {
048
049 /**
050 * Constructs an alterer with a given recombination probability.
051 *
052 * @param probability the crossover probability.
053 * @throws IllegalArgumentException if the {@code probability} is not in the
054 * valid range of {@code [0, 1]}.
055 */
056 public SwapMutator(final double probability) {
057 super(probability);
058 }
059
060 /**
061 * Default constructor, with default mutation probability
062 * ({@link AbstractAlterer#DEFAULT_ALTER_PROBABILITY}).
063 */
064 public SwapMutator() {
065 this(DEFAULT_ALTER_PROBABILITY);
066 }
067
068 /**
069 * Swaps the genes in the given array, with the mutation probability of this
070 * mutation.
071 */
072 @Override
073 protected MutatorResult<Chromosome<G>> mutate(
074 final Chromosome<G> chromosome,
075 final double p,
076 final Random random
077 ) {
078 final MutatorResult<Chromosome<G>> result;
079 if (chromosome.length() > 1) {
080 final MSeq<G> genes = chromosome.toSeq().copy();
081 final int mutations = (int)indexes(random, genes.length(), p)
082 .peek(i -> genes.swap(i, random.nextInt(genes.length())))
083 .count();
084 result = MutatorResult.of(
085 chromosome.newInstance(genes.toISeq()),
086 mutations
087 );
088 } else {
089 result = MutatorResult.of(chromosome);
090 }
091
092 return result;
093 }
094
095 @Override
096 public int hashCode() {
097 return Hash.of(getClass()).and(super.hashCode()).value();
098 }
099
100 @Override
101 public boolean equals(final Object obj) {
102 return Equality.of(this, obj).test(super::equals);
103 }
104
105 @Override
106 public String toString() {
107 return format("%s[p=%f]", getClass().getSimpleName(), _probability);
108 }
109
110 }
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