001 /*
002 * Java Genetic Algorithm Library (jenetics-4.2.0).
003 * Copyright (c) 2007-2018 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
024 import java.util.Random;
025
026 import io.jenetics.internal.math.comb;
027 import io.jenetics.internal.util.Equality;
028 import io.jenetics.internal.util.Hash;
029 import io.jenetics.util.MSeq;
030 import io.jenetics.util.RandomRegistry;
031
032 /**
033 * The {@code PartiallyMatchedCrossover} (PMX) guarantees that all {@link Gene}s
034 * are found exactly once in each chromosome. No gene is duplicated by this
035 * crossover. The PMX can be applied usefully in the TSP or other permutation
036 * problem encodings. Permutation encoding is useful for all problems where the
037 * fitness only depends on the ordering of the genes within the chromosome. This
038 * is the case in many combinatorial optimization problems. Other crossover
039 * operators for combinatorial optimization are:
040 * <ul type="square">
041 * <li>order crossover</li>
042 * <li>cycle crossover</li>
043 * <li>edge recombination crossover</li>
044 * <li>edge assembly crossover</li>
045 * </ul>
046 * <p>
047 * The PMX is similar to the two-point crossover. A crossing region is chosen
048 * by selecting two crossing points.
049 * <pre>
050 * C1 = 012|345|6789
051 * C2 = 987|654|3210
052 * </pre>
053 * After performing the crossover we normally got two invalid chromosomes.
054 * <pre>
055 * C1 = 012|654|6789
056 * C2 = 987|345|3210
057 * </pre>
058 * Chromosome {@code C1} contains the value 6 twice and misses the value
059 * 3. On the other side chromosome {@code C2} contains the value 3 twice and
060 * misses the value 6. We can observe that this crossover is equivalent
061 * to the exchange of the values {@code 3 -> 6}, {@code 4 -> 5} and
062 * {@code 5 -> 4}. To repair the two
063 * chromosomes we have to apply this exchange outside the crossing region.
064 * <pre>
065 * C1 = 012|654|3789
066 * C2 = 987|345|6210
067 * </pre>
068 *
069 * <em>The {@code PartiallyMatchedCrossover} class requires chromosomes with the
070 * same length. An {@code IllegalArgumentException} is thrown at runtime if this
071 * requirement is not fulfilled.</em>
072 *
073 * @see PermutationChromosome
074 *
075 * @author <a href="mailto:franz.wilhelmstoetter@gmail.com">Franz Wilhelmstötter</a>
076 * @since 1.0
077 * @version 4.0
078 */
079 public final class PartiallyMatchedCrossover<T, C extends Comparable<? super C>>
080 extends Crossover<EnumGene<T>, C>
081 {
082
083 public PartiallyMatchedCrossover(final double probability) {
084 super(probability);
085 }
086
087 @Override
088 protected int crossover(
089 final MSeq<EnumGene<T>> that,
090 final MSeq<EnumGene<T>> other
091 ) {
092 if (that.length() != other.length()) {
093 throw new IllegalArgumentException(format(
094 "Required chromosomes with same length: %s != %s",
095 that.length(), other.length()
096 ));
097 }
098
099 if (that.length() >= 2) {
100 final Random random = RandomRegistry.getRandom();
101 final int[] points = comb.subset(that.length(), 2, random);
102
103 that.swap(points[0], points[1], other, points[0]);
104 repair(that, other, points[0], points[1]);
105 repair(other, that, points[0], points[1]);
106 }
107
108 return 1;
109 }
110
111 private static <T> void repair(
112 final MSeq<T> that, final MSeq<T> other,
113 final int begin, final int end
114 ) {
115 for (int i = 0; i < begin; ++i) {
116 int index = that.indexOf(that.get(i), begin, end);
117 while (index != -1) {
118 that.set(i, other.get(index));
119 index = that.indexOf(that.get(i), begin, end);
120 }
121 }
122 for (int i = end, n = that.length(); i < n; ++i) {
123 int index = that.indexOf(that.get(i), begin, end);
124 while (index != -1) {
125 that.set(i, other.get(index));
126 index = that.indexOf(that.get(i), begin, end);
127 }
128 }
129 }
130
131 @Override
132 public int hashCode() {
133 return Hash.of(getClass()).and(super.hashCode()).value();
134 }
135
136 @Override
137 public boolean equals(final Object obj) {
138 return Equality.of(this, obj).test(super::equals);
139 }
140
141 @Override
142 public String toString() {
143 return format("%s[p=%f]", getClass().getSimpleName(), _probability);
144 }
145
146 }
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