001 /*
002 * Java Genetic Algorithm Library (jenetics-1.5.0).
003 * Copyright (c) 2007-2013 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 import static org.jenetics.util.object.hashCodeOf;
025
026 import java.util.Random;
027
028 import org.jenetics.util.MSeq;
029 import org.jenetics.util.RandomRegistry;
030 import org.jenetics.util.math;
031
032 /**
033 * <strong><p>Multiple point crossover</p></strong>
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><div align="center">
040 * <img src="doc-files/2PointCrossover.svg" width="400" alt="2-point crossover">
041 * </div></p>
042 *
043 * If the number of crossover points is odd, the crossover looks like in the
044 * following figure.
045 *
046 * <p><div align="center">
047 * <img src="doc-files/3PointCrossover.svg" width="400" alt="3-point crossover">
048 * </div></p>
049 *
050 * @see SinglePointCrossover
051 *
052 * @author <a href="mailto:franz.wilhelmstoetter@gmx.at">Franz Wilhelmstötter</a>
053 * @since 1.2
054 * @version 1.2 — <em>$Date: 2013-11-28 $ </em>
055 */
056 public class MultiPointCrossover<G extends Gene<?, G>> extends Crossover<G> {
057
058 private final int _n;
059
060 /**
061 * Create a new crossover instance.
062 *
063 * @param probability the recombination probability.
064 * @param n the number of crossover points.
065 * @throws IllegalArgumentException if the {@code probability} is not in the
066 * valid range of {@code [0, 1]} or {@code n < 1}.
067 */
068 public MultiPointCrossover(final double probability, final int n) {
069 super(probability);
070 if (n < 1) {
071 throw new IllegalArgumentException(format(
072 "n must be at least 1 but was %d.", n
073 ));
074 }
075 _n = n;
076 }
077
078 /**
079 * Create a new crossover instance with two crossover points.
080 *
081 * @param probability the recombination probability.
082 * @throws IllegalArgumentException if the {@code probability} is not in the
083 * valid range of {@code [0, 1]}.
084 */
085 public MultiPointCrossover(final double probability) {
086 this(probability, 2);
087 }
088
089 /**
090 * Create a new crossover instance with default crossover probability of
091 * 0.05.
092 *
093 * @param n the number of crossover points.
094 * @throws IllegalArgumentException if {@code n < 1}.
095 */
096 public MultiPointCrossover(final int n) {
097 this(0.05, n);
098 }
099
100 /**
101 * Create a new crossover instance with two crossover points and crossover
102 * probability 0.05.
103 */
104 public MultiPointCrossover() {
105 this(0.05, 2);
106 }
107
108 /**
109 * Return the number of crossover points.
110 *
111 * @return the number of crossover points.
112 */
113 public int getN() {
114 return _n;
115 }
116
117 @Override
118 protected int crossover(final MSeq<G> that, final MSeq<G> other) {
119 assert (that.length() == other.length());
120
121 final int n = that.length();
122 final int k = min(n, _n);
123
124 final Random random = RandomRegistry.getRandom();
125 final int[] points = k > 0 ? math.subset(n, k, random) : new int[0];
126
127 crossover(that, other, points);
128 return 2;
129 }
130
131 // Package private for testing purpose.
132 static <T> void crossover(
133 final MSeq<T> that,
134 final MSeq<T> other,
135 final int[] indexes
136 ) {
137
138 for (int i = 0; i < indexes.length - 1; i += 2) {
139 final int start = indexes[i];
140 final int end = indexes[i + 1];
141 that.swap(start, end, other, start);
142 }
143 if (indexes.length%2 == 1) {
144 final int index = indexes[indexes.length - 1];
145 that.swap(index, that.length(), other, index);
146 }
147 }
148
149 @Override
150 public int hashCode() {
151 return hashCodeOf(getClass()).
152 and(super.hashCode()).
153 and(_n).value();
154 }
155
156 @Override
157 public boolean equals(final Object obj) {
158 if (obj == this) {
159 return true;
160 }
161 if (obj == null || obj.getClass() != getClass()) {
162 return false;
163 }
164
165 final MultiPointCrossover<?> mpc = (MultiPointCrossover<?>)obj;
166 return _n == mpc._n && super.equals(obj);
167 }
168
169 @Override
170 public String toString() {
171 return format(
172 "%s[p=%f, n=%d]",
173 getClass().getSimpleName(), _probability, _n
174 );
175 }
176
177 //public static <G extends Gene<?, G>> MultiPointCrossover<G> zip() {
178 // return new MultiPointCrossover<>(Integer.MAX_VALUE);
179 //}
180
181 }
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