001 /*
002 * Java Genetic Algorithm Library (jenetics-6.3.0).
003 * Copyright (c) 2007-2021 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.ext;
021
022 import java.util.Random;
023
024 import io.jenetics.AbstractAlterer;
025 import io.jenetics.Chromosome;
026 import io.jenetics.Gene;
027 import io.jenetics.Mutator;
028 import io.jenetics.MutatorResult;
029 import io.jenetics.internal.math.Combinatorics;
030 import io.jenetics.internal.math.Probabilities;
031 import io.jenetics.util.MSeq;
032
033 /**
034 * The Hybridizing PSM and RSM Operator (HPRM) constructs an offspring from a
035 * pair of parents by hybridizing two mutation operators, PSM and RSM.
036 * <p>
037 * This mutator is described in <a href="https://arxiv.org/abs/1203.5028">A New
038 * Mutation Operator for Solving an NP-Complete Problem: Travelling Salesman
039 * Problem</a>, by <em>Otman Abdoun, Chakir Tajani</em> and
040 * <em>Jaafar Abouchabka</em>.
041 *
042 * @see RSMutator
043 * @see io.jenetics.SwapMutator
044 *
045 * @author <a href="mailto:franz.wilhelmstoetter@gmail.com">Franz Wilhelmstötter</a>
046 * @version 5.0
047 * @since 5.0
048 */
049 public class HPRMutator<
050 G extends Gene<?, G>,
051 C extends Comparable<? super C>
052 >
053 extends Mutator<G, C>
054 {
055
056 /**
057 * Constructs an alterer with a given recombination probability.
058 *
059 * @param probability the crossover probability.
060 * @throws IllegalArgumentException if the {@code probability} is not in the
061 * valid range of {@code [0, 1]}.
062 */
063 public HPRMutator(final double probability) {
064 super(probability);
065 }
066
067 /**
068 * Default constructor, with default mutation probability
069 * ({@link AbstractAlterer#DEFAULT_ALTER_PROBABILITY}).
070 */
071 public HPRMutator() {
072 this(DEFAULT_ALTER_PROBABILITY);
073 }
074
075 @Override
076 protected MutatorResult<Chromosome<G>> mutate(
077 final Chromosome<G> chromosome,
078 final double p,
079 final Random random
080 ) {
081 final MutatorResult<Chromosome<G>> result;
082 if (chromosome.length() > 1) {
083 final int P = Probabilities.toInt(p);
084 final int[] points = Combinatorics.subset(chromosome.length(), 2);
085 final MSeq<G> genes = MSeq.of(chromosome);
086
087 int mutations = (points[1] - points[0] + 1)/2;
088 for (int i = points[0], j = points[1]; i < j; ++i, --j) {
089 genes.swap(i, j);
090 if (random.nextInt() < P) {
091 genes.swap(i, random.nextInt(chromosome.length()));
092 ++mutations;
093 }
094 }
095
096 result = MutatorResult.of(
097 chromosome.newInstance(genes.toISeq()),
098 mutations
099 );
100 } else {
101 result = MutatorResult.of(chromosome);
102 }
103
104 return result;
105 }
106
107 }
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