001 /*
002 * Java Genetic Algorithm Library (jenetics-3.8.0).
003 * Copyright (c) 2007-2017 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.Equality;
028 import org.jenetics.internal.util.Hash;
029
030 import org.jenetics.util.MSeq;
031 import org.jenetics.util.RandomRegistry;
032
033 /**
034 * <strong>Single point crossover</strong>
035 *
036 * <p>
037 * One or two children are created by taking two parent strings and cutting
038 * them at some randomly chosen site. E.g.
039 * <p>
040 * <img src="doc-files/SinglePointCrossover.svg" width="400"
041 * alt="Single-point crossover" >
042 * <p>
043 * If we create a child and its complement we preserving the total number of
044 * genes in the population, preventing any genetic drift.
045 * Single-point crossover is the classic form of crossover. However, it produces
046 * very slow mixing compared with multi-point crossover or uniform crossover.
047 * For problems where the site position has some intrinsic meaning to the
048 * problem single-point crossover can lead to small disruption than multi-point
049 * or uniform crossover.
050 *
051 * @see MultiPointCrossover
052 *
053 * @author <a href="mailto:franz.wilhelmstoetter@gmx.at">Franz Wilhelmstötter</a>
054 * @since 1.0
055 * @version 3.6
056 */
057 public class SinglePointCrossover<
058 G extends Gene<?, G>,
059 C extends Comparable<? super C>
060 >
061 extends MultiPointCrossover<G, C>
062 {
063
064 /**
065 * Constructs an alterer with a given recombination probability.
066 *
067 * @param probability the crossover probability.
068 * @throws IllegalArgumentException if the {@code probability} is not in the
069 * valid range of {@code [0, 1]}.
070 */
071 public SinglePointCrossover(final double probability) {
072 super(probability, 1);
073 }
074
075 /**
076 * Create a new single point crossover object with crossover probability of
077 * {@code 0.05}.
078 */
079 public SinglePointCrossover() {
080 this(0.05);
081 }
082
083 @Override
084 protected int crossover(final MSeq<G> that, final MSeq<G> other) {
085 final Random random = RandomRegistry.getRandom();
086
087 final int index = random.nextInt(min(that.length(), other.length()));
088 crossover(that, other, index);
089 return 2;
090 }
091
092 // Package private for testing purpose.
093 static <T> void crossover(
094 final MSeq<T> that,
095 final MSeq<T> other,
096 final int index
097 ) {
098 assert index >= 0 :
099 format(
100 "Crossover index must be within [0, %d) but was %d",
101 that.length(), index
102 );
103
104 that.swap(index, min(that.length(), other.length()), other, index);
105 }
106
107 @Override
108 public int hashCode() {
109 return Hash.of(getClass()).and(super.hashCode()).value();
110 }
111
112 @Override
113 public boolean equals(final Object obj) {
114 return Equality.of(this, obj).test(super::equals);
115 }
116
117 @Override
118 public String toString() {
119 return format("%s[p=%f]", getClass().getSimpleName(), _probability);
120 }
121
122 }
|