001 /*
002 * Java Genetic Algorithm Library (jenetics-1.6.0).
003 * Copyright (c) 2007-2014 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 javolution.lang.Immutable;
027
028 import org.jenetics.internal.util.HashBuilder;
029
030 import org.jenetics.util.MSeq;
031 import org.jenetics.util.RandomRegistry;
032 import org.jenetics.util.math;
033
034 /**
035 * <p>
036 * The {@code PartiallyMatchedCrossover} (PMX) guarantees that all {@link Gene}s
037 * are found exactly once in each chromosome. No gene is duplicated by this
038 * crossover. The PMX can be applied usefully in the TSP or other permutation
039 * problem encodings. Permutation encoding is useful for all problems where the
040 * fitness only depends on the ordering of the genes within the chromosome. This
041 * is the case in many combinatorial optimization problems. Other crossover
042 * operators for combinatorial optimization are:
043 * <ul type="square">
044 * <li>order crossover</li>
045 * <li>cycle crossover</li>
046 * <li>edge recombination crossover</li>
047 * <li>edge assembly crossover</li>
048 * </ul>
049 * </p>
050 * The PMX is similar to the two-point crossover. A crossing region is chosen
051 * by selecting two crossing points.
052 * <pre>
053 * C1 = 012|345|6789
054 * C2 = 987|654|3210
055 * </pre>
056 * After performing the crossover we normally got two invalid chromosomes.
057 * <pre>
058 * C1 = 012|654|6789
059 * C2 = 987|345|3210
060 * </pre>
061 * Chromosome {@code C1} contains the value 6 twice and misses the value
062 * 3. On the other side chromosome {@code C2} contains the value 3 twice and
063 * misses the value 6. We can observe that this crossover is equivalent
064 * to the exchange of the values 3 -> 6, 4 -> 5 and 5 -> 4. To repair the two
065 * chromosomes we have to apply this exchange outside the crossing region.
066 * <pre>
067 * C1 = 012|654|3789
068 * C2 = 987|345|6210
069 * </pre>
070 *
071 * @see PermutationChromosome
072 *
073 * @author <a href="mailto:franz.wilhelmstoetter@gmx.at">Franz Wilhelmstötter</a>
074 * @since 1.0
075 * @version 1.0 — <em>$Date: 2014-02-27 $</em>
076 */
077 public final class PartiallyMatchedCrossover<T>
078 extends Crossover<EnumGene<T>>
079 implements Immutable
080 {
081
082 public PartiallyMatchedCrossover(final double probability) {
083 super(probability);
084 }
085
086 @Override
087 protected int crossover(
088 final MSeq<EnumGene<T>> that,
089 final MSeq<EnumGene<T>> other
090 ) {
091 assert (that.length() == other.length());
092
093 if (that.length() >= 2) {
094 final Random random = RandomRegistry.getRandom();
095 final int[] points = math.subset(that.length(), 2, random);
096
097 that.swap(points[0], points[1], other, points[0]);
098 repair(that, other, points[0], points[1]);
099 repair(other, that, points[0], points[1]);
100 }
101
102 return 1;
103 }
104
105 private static <T> void repair(
106 final MSeq<T> that, final MSeq<T> other,
107 final int begin, final int end
108 ) {
109 for (int i = 0; i < begin; ++i) {
110 int index = that.indexOf(that.get(i), begin, end);
111 while (index != -1) {
112 that.set(i, other.get(index));
113 index = that.indexOf(that.get(i), begin, end);
114 }
115 }
116 for (int i = end, n = that.length(); i < n; ++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 }
124
125 @Override
126 public int hashCode() {
127 return HashBuilder.of(getClass()).and(super.hashCode()).value();
128 }
129
130 @Override
131 public boolean equals(final Object obj) {
132 if (obj == this) {
133 return true;
134 }
135 if (obj == null || obj.getClass() != getClass()) {
136 return false;
137 }
138
139 return super.equals(obj);
140 }
141
142 @Override
143 public String toString() {
144 return format("%s[p=%f]", getClass().getSimpleName(), _probability);
145 }
146
147 }
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