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.Math.min;
023 import static java.lang.String.format;
024
025 import java.util.Random;
026
027 import org.jenetics.internal.util.HashBuilder;
028
029 import org.jenetics.util.MSeq;
030 import org.jenetics.util.RandomRegistry;
031 import org.jenetics.util.math;
032
033 /**
034 * <strong><p>Multiple point crossover</p></strong>
035 *
036 * If the {@code MultiPointCrossover} is created with one crossover point, it
037 * behaves exactly like the {@link SinglePointCrossover}. The following picture
038 * shows how the {@code MultiPointCrossover} works with two crossover points,
039 * defined at index 1 and 4.
040 * <p><div align="center">
041 * <img src="doc-files/2PointCrossover.svg" width="400" alt="2-point crossover">
042 * </div></p>
043 *
044 * If the number of crossover points is odd, the crossover looks like in the
045 * following figure.
046 *
047 * <p><div align="center">
048 * <img src="doc-files/3PointCrossover.svg" width="400" alt="3-point crossover">
049 * </div></p>
050 *
051 * @see SinglePointCrossover
052 *
053 * @author <a href="mailto:franz.wilhelmstoetter@gmx.at">Franz Wilhelmstötter</a>
054 * @since 1.2
055 * @version 1.2 — <em>$Date: 2014-02-27 $ </em>
056 */
057 public class MultiPointCrossover<G extends Gene<?, G>> extends Crossover<G> {
058
059 private final int _n;
060
061 /**
062 * Create a new crossover instance.
063 *
064 * @param probability the recombination probability.
065 * @param n the number of crossover points.
066 * @throws IllegalArgumentException if the {@code probability} is not in the
067 * valid range of {@code [0, 1]} or {@code n < 1}.
068 */
069 public MultiPointCrossover(final double probability, final int n) {
070 super(probability);
071 if (n < 1) {
072 throw new IllegalArgumentException(format(
073 "n must be at least 1 but was %d.", n
074 ));
075 }
076 _n = n;
077 }
078
079 /**
080 * Create a new crossover instance with two crossover points.
081 *
082 * @param probability the recombination probability.
083 * @throws IllegalArgumentException if the {@code probability} is not in the
084 * valid range of {@code [0, 1]}.
085 */
086 public MultiPointCrossover(final double probability) {
087 this(probability, 2);
088 }
089
090 /**
091 * Create a new crossover instance with default crossover probability of
092 * 0.05.
093 *
094 * @param n the number of crossover points.
095 * @throws IllegalArgumentException if {@code n < 1}.
096 */
097 public MultiPointCrossover(final int n) {
098 this(0.05, n);
099 }
100
101 /**
102 * Create a new crossover instance with two crossover points and crossover
103 * probability 0.05.
104 */
105 public MultiPointCrossover() {
106 this(0.05, 2);
107 }
108
109 /**
110 * Return the number of crossover points.
111 *
112 * @return the number of crossover points.
113 */
114 public int getN() {
115 return _n;
116 }
117
118 @Override
119 protected int crossover(final MSeq<G> that, final MSeq<G> other) {
120 assert (that.length() == other.length());
121
122 final int n = that.length();
123 final int k = min(n, _n);
124
125 final Random random = RandomRegistry.getRandom();
126 final int[] points = k > 0 ? math.subset(n, k, random) : new int[0];
127
128 crossover(that, other, points);
129 return 2;
130 }
131
132 // Package private for testing purpose.
133 static <T> void crossover(
134 final MSeq<T> that,
135 final MSeq<T> other,
136 final int[] indexes
137 ) {
138
139 for (int i = 0; i < indexes.length - 1; i += 2) {
140 final int start = indexes[i];
141 final int end = indexes[i + 1];
142 that.swap(start, end, other, start);
143 }
144 if (indexes.length%2 == 1) {
145 final int index = indexes[indexes.length - 1];
146 that.swap(index, that.length(), other, index);
147 }
148 }
149
150 @Override
151 public int hashCode() {
152 return HashBuilder.of(getClass()).
153 and(super.hashCode()).
154 and(_n).value();
155 }
156
157 @Override
158 public boolean equals(final Object obj) {
159 if (obj == this) {
160 return true;
161 }
162 if (obj == null || obj.getClass() != getClass()) {
163 return false;
164 }
165
166 final MultiPointCrossover<?> mpc = (MultiPointCrossover<?>)obj;
167 return _n == mpc._n && super.equals(obj);
168 }
169
170 @Override
171 public String toString() {
172 return format(
173 "%s[p=%f, n=%d]",
174 getClass().getSimpleName(), _probability, _n
175 );
176 }
177
178 //public static <G extends Gene<?, G>> MultiPointCrossover<G> zip() {
179 // return new MultiPointCrossover<>(Integer.MAX_VALUE);
180 //}
181
182 }
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