001 /*
002 * Java Genetic Algorithm Library (jenetics-4.3.0).
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.Math.min;
023 import static java.lang.String.format;
024 import static io.jenetics.internal.util.Hashes.hash;
025
026 import java.util.Random;
027
028 import io.jenetics.internal.math.comb;
029 import io.jenetics.util.MSeq;
030 import io.jenetics.util.RandomRegistry;
031
032 /**
033 * <p><strong>Multiple point crossover</strong></p>
034 *
035 * If the {@code MultiPointCrossover} is created with one crossover point, it
036 * behaves exactly like the {@link SinglePointCrossover}. The following picture
037 * shows how the {@code MultiPointCrossover} works with two crossover points,
038 * defined at index 1 and 4.
039 * <p>
040 * <img src="doc-files/2PointCrossover.svg" width="400" alt="2-point crossover">
041 * </p>
042 *
043 * If the number of crossover points is odd, the crossover looks like in the
044 * following figure.
045 *
046 * <p>
047 * <img src="doc-files/3PointCrossover.svg" width="400" alt="3-point crossover">
048 * </p>
049 *
050 * @see SinglePointCrossover
051 *
052 * @author <a href="mailto:franz.wilhelmstoetter@gmail.com">Franz Wilhelmstötter</a>
053 * @since 1.2
054 * @version 4.0
055 */
056 public class MultiPointCrossover<
057 G extends Gene<?, G>,
058 C extends Comparable<? super C>
059 >
060 extends Crossover<G, C>
061 {
062
063 private final int _n;
064
065 /**
066 * Create a new crossover instance.
067 *
068 * @param probability the recombination probability.
069 * @param n the number of crossover points.
070 * @throws IllegalArgumentException if the {@code probability} is not in the
071 * valid range of {@code [0, 1]} or {@code n < 1}.
072 */
073 public MultiPointCrossover(final double probability, final int n) {
074 super(probability);
075 if (n < 1) {
076 throw new IllegalArgumentException(format(
077 "n must be at least 1 but was %d.", n
078 ));
079 }
080 _n = n;
081 }
082
083 /**
084 * Create a new crossover instance with two crossover points.
085 *
086 * @param probability the recombination probability.
087 * @throws IllegalArgumentException if the {@code probability} is not in the
088 * valid range of {@code [0, 1]}.
089 */
090 public MultiPointCrossover(final double probability) {
091 this(probability, 2);
092 }
093
094 /**
095 * Create a new crossover instance with default crossover probability of
096 * 0.05.
097 *
098 * @param n the number of crossover points.
099 * @throws IllegalArgumentException if {@code n < 1}.
100 */
101 public MultiPointCrossover(final int n) {
102 this(0.05, n);
103 }
104
105 /**
106 * Create a new crossover instance with two crossover points and crossover
107 * probability 0.05.
108 */
109 public MultiPointCrossover() {
110 this(0.05, 2);
111 }
112
113 /**
114 * Return the number of crossover points.
115 *
116 * @return the number of crossover points.
117 */
118 public int getN() {
119 return _n;
120 }
121
122 @Override
123 protected int crossover(final MSeq<G> that, final MSeq<G> other) {
124 assert that.length() == other.length();
125
126 final int n = min(that.length(), other.length());
127 final int k = min(n, _n);
128
129 final Random random = RandomRegistry.getRandom();
130 final int[] points = k > 0 ? comb.subset(n, k, random) : new int[0];
131
132 crossover(that, other, points);
133 return 2;
134 }
135
136 // Package private for testing purpose.
137 static <T> void crossover(
138 final MSeq<T> that,
139 final MSeq<T> other,
140 final int[] indexes
141 ) {
142
143 for (int i = 0; i < indexes.length - 1; i += 2) {
144 final int start = indexes[i];
145 final int end = indexes[i + 1];
146 that.swap(start, end, other, start);
147 }
148 if (indexes.length%2 == 1) {
149 final int index = indexes[indexes.length - 1];
150 that.swap(index, min(that.length(), other.length()), other, index);
151 }
152 }
153
154 @Override
155 public int hashCode() {
156 return hash(super.hashCode(), hash(_n));
157 }
158
159 @Override
160 public boolean equals(final Object obj) {
161 return obj == this ||
162 obj != null &&
163 getClass() == obj.getClass() &&
164 _n == ((MultiPointCrossover)obj)._n &&
165 super.equals(obj);
166 }
167
168 @Override
169 public String toString() {
170 return format(
171 "%s[p=%f, n=%d]",
172 getClass().getSimpleName(), _probability, _n
173 );
174 }
175
176 }
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