001 /*
002 * Java Genetic Algorithm Library (jenetics-3.9.0).
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@gmx.at)
019 */
020 package org.jenetics;
021
022 import static java.lang.String.format;
023
024 import java.util.Random;
025
026 import org.jenetics.internal.math.base;
027 import org.jenetics.internal.util.Equality;
028 import org.jenetics.internal.util.Hash;
029
030 import org.jenetics.util.MSeq;
031 import org.jenetics.util.RandomRegistry;
032
033 /**
034 * The {@code PartiallyMatchedCrossover} (PMX) guarantees that all {@link Gene}s
035 * are found exactly once in each chromosome. No gene is duplicated by this
036 * crossover. The PMX can be applied usefully in the TSP or other permutation
037 * problem encodings. Permutation encoding is useful for all problems where the
038 * fitness only depends on the ordering of the genes within the chromosome. This
039 * is the case in many combinatorial optimization problems. Other crossover
040 * operators for combinatorial optimization are:
041 * <ul type="square">
042 * <li>order crossover</li>
043 * <li>cycle crossover</li>
044 * <li>edge recombination crossover</li>
045 * <li>edge assembly crossover</li>
046 * </ul>
047 * <p>
048 * The PMX is similar to the two-point crossover. A crossing region is chosen
049 * by selecting two crossing points.
050 * <pre>
051 * C1 = 012|345|6789
052 * C2 = 987|654|3210
053 * </pre>
054 * After performing the crossover we normally got two invalid chromosomes.
055 * <pre>
056 * C1 = 012|654|6789
057 * C2 = 987|345|3210
058 * </pre>
059 * Chromosome {@code C1} contains the value 6 twice and misses the value
060 * 3. On the other side chromosome {@code C2} contains the value 3 twice and
061 * misses the value 6. We can observe that this crossover is equivalent
062 * to the exchange of the values {@code 3 -> 6}, {@code 4 -> 5} and
063 * {@code 5 -> 4}. To repair the two
064 * chromosomes we have to apply this exchange outside the crossing region.
065 * <pre>
066 * C1 = 012|654|3789
067 * C2 = 987|345|6210
068 * </pre>
069 *
070 * <em>The {@code PartiallyMatchedCrossover} class requires chromosomes with the
071 * same length. An {@code IllegalArgumentException} is thrown at runtime if this
072 * requirement is not fulfilled.</em>
073 *
074 * @see PermutationChromosome
075 *
076 * @author <a href="mailto:franz.wilhelmstoetter@gmx.at">Franz Wilhelmstötter</a>
077 * @since 1.0
078 * @version 3.6
079 */
080 public final class PartiallyMatchedCrossover<T, C extends Comparable<? super C>>
081 extends Crossover<EnumGene<T>, C>
082 {
083
084 public PartiallyMatchedCrossover(final double probability) {
085 super(probability);
086 }
087
088 @Override
089 protected int crossover(
090 final MSeq<EnumGene<T>> that,
091 final MSeq<EnumGene<T>> other
092 ) {
093 if (that.length() != other.length()) {
094 throw new IllegalArgumentException(format(
095 "Required chromosomes with same length: %s != %s",
096 that.length(), other.length()
097 ));
098 }
099
100 if (that.length() >= 2) {
101 final Random random = RandomRegistry.getRandom();
102 final int[] points = base.subset(that.length(), 2, random);
103
104 that.swap(points[0], points[1], other, points[0]);
105 repair(that, other, points[0], points[1]);
106 repair(other, that, points[0], points[1]);
107 }
108
109 return 1;
110 }
111
112 private static <T> void repair(
113 final MSeq<T> that, final MSeq<T> other,
114 final int begin, final int end
115 ) {
116 for (int i = 0; i < begin; ++i) {
117 int index = that.indexOf(that.get(i), begin, end);
118 while (index != -1) {
119 that.set(i, other.get(index));
120 index = that.indexOf(that.get(i), begin, end);
121 }
122 }
123 for (int i = end, n = that.length(); i < n; ++i) {
124 int index = that.indexOf(that.get(i), begin, end);
125 while (index != -1) {
126 that.set(i, other.get(index));
127 index = that.indexOf(that.get(i), begin, end);
128 }
129 }
130 }
131
132 @Override
133 public int hashCode() {
134 return Hash.of(getClass()).and(super.hashCode()).value();
135 }
136
137 @Override
138 public boolean equals(final Object obj) {
139 return Equality.of(this, obj).test(super::equals);
140 }
141
142 @Override
143 public String toString() {
144 return format("%s[p=%f]", getClass().getSimpleName(), _probability);
145 }
146
147 }
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