001 /*
002 * Java Genetic Algorithm Library (jenetics-3.5.0).
003 * Copyright (c) 2007-2016 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 * @see PermutationChromosome
071 *
072 * @author <a href="mailto:franz.wilhelmstoetter@gmx.at">Franz Wilhelmstötter</a>
073 * @since 1.0
074 * @version 3.0
075 */
076 public final class PartiallyMatchedCrossover<T, C extends Comparable<? super C>>
077 extends Crossover<EnumGene<T>, C>
078 {
079
080 public PartiallyMatchedCrossover(final double probability) {
081 super(probability);
082 }
083
084 @Override
085 protected int crossover(
086 final MSeq<EnumGene<T>> that,
087 final MSeq<EnumGene<T>> other
088 ) {
089 assert that.length() == other.length();
090
091 if (that.length() >= 2) {
092 final Random random = RandomRegistry.getRandom();
093 final int[] points = base.subset(that.length(), 2, random);
094
095 that.swap(points[0], points[1], other, points[0]);
096 repair(that, other, points[0], points[1]);
097 repair(other, that, points[0], points[1]);
098 }
099
100 return 1;
101 }
102
103 private static <T> void repair(
104 final MSeq<T> that, final MSeq<T> other,
105 final int begin, final int end
106 ) {
107 for (int i = 0; i < begin; ++i) {
108 int index = that.indexOf(that.get(i), begin, end);
109 while (index != -1) {
110 that.set(i, other.get(index));
111 index = that.indexOf(that.get(i), begin, end);
112 }
113 }
114 for (int i = end, n = that.length(); i < n; ++i) {
115 int index = that.indexOf(that.get(i), begin, end);
116 while (index != -1) {
117 that.set(i, other.get(index));
118 index = that.indexOf(that.get(i), begin, end);
119 }
120 }
121 }
122
123 @Override
124 public int hashCode() {
125 return Hash.of(getClass()).and(super.hashCode()).value();
126 }
127
128 @Override
129 public boolean equals(final Object obj) {
130 return Equality.of(this, obj).test(super::equals);
131 }
132
133 @Override
134 public String toString() {
135 return format("%s[p=%f]", getClass().getSimpleName(), _probability);
136 }
137
138 }
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