001 /*
002 * Java Genetic Algorithm Library (jenetics-2.0.2).
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 org.jenetics.internal.util.HashBuilder;
027
028 import org.jenetics.util.MSeq;
029 import org.jenetics.util.RandomRegistry;
030
031
032 /**
033 * <strong>Single point crossover</strong>
034 *
035 * <p>
036 * One or two children are created by taking two parent strings and cutting
037 * them at some randomly chosen site. E.g.
038 * <p>
039 * <img src="doc-files/SinglePointCrossover.svg" width="400"
040 * alt="Single-point crossover" >
041 * <p>
042 * If we create a child and its complement we preserving the total number of
043 * genes in the population, preventing any genetic drift.
044 * Single-point crossover is the classic form of crossover. However, it produces
045 * very slow mixing compared with multi-point crossover or uniform crossover.
046 * For problems where the site position has some intrinsic meaning to the
047 * problem single-point crossover can lead to small disruption than multi-point
048 * or uniform crossover.
049 *
050 * @see MultiPointCrossover
051 *
052 * @author <a href="mailto:franz.wilhelmstoetter@gmx.at">Franz Wilhelmstötter</a>
053 * @since 1.0
054 * @version 2.0 — <em>$Date: 2014-03-28 $</em>
055 */
056 public class SinglePointCrossover<G extends Gene<?, G>>
057 extends MultiPointCrossover<G>
058 {
059
060 /**
061 * Constructs an alterer with a given recombination probability.
062 *
063 * @param probability the crossover probability.
064 * @throws IllegalArgumentException if the {@code probability} is not in the
065 * valid range of {@code [0, 1]}.
066 */
067 public SinglePointCrossover(final double probability) {
068 super(probability, 1);
069 }
070
071 /**
072 * Create a new single point crossover object with crossover probability of
073 * {@code 0.05}.
074 */
075 public SinglePointCrossover() {
076 this(0.05);
077 }
078
079
080
081 @Override
082 protected int crossover(final MSeq<G> that, final MSeq<G> other) {
083 assert (that.length() == other.length());
084
085 final Random random = RandomRegistry.getRandom();
086 crossover(that, other, random.nextInt(that.length()));
087 return 2;
088 }
089
090 // Package private for testing purpose.
091 static <T> void crossover(
092 final MSeq<T> that,
093 final MSeq<T> other,
094 final int index
095 ) {
096 assert (index >= 0) : format(
097 "Crossover index must be within [0, %d) but was %d",
098 that.length(), index
099 );
100
101 that.swap(index, that.length(), other, index);
102 }
103
104 @Override
105 public int hashCode() {
106 return HashBuilder.of(getClass()).and(super.hashCode()).value();
107 }
108
109 @Override
110 public boolean equals(final Object obj) {
111 if (obj == this) {
112 return true;
113 }
114 if (obj == null || obj.getClass() != getClass()) {
115 return false;
116 }
117
118 return super.equals(obj);
119 }
120
121 @Override
122 public String toString() {
123 return format("%s[p=%f]", getClass().getSimpleName(), _probability);
124 }
125
126 }
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