001 /*
002 * Java Genetic Algorithm Library (jenetics-8.0.0).
003 * Copyright (c) 2007-2024 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
025 import io.jenetics.util.MSeq;
026 import io.jenetics.util.RandomRegistry;
027
028 /**
029 * <strong>Single point crossover</strong>
030 *
031 * <p>
032 * One or two children are created by taking two parent strings and cutting
033 * them at some randomly chosen site. E.g.
034 * <p>
035 * <img src="doc-files/SinglePointCrossover.svg" width="400"
036 * alt="Single-point crossover" >
037 * <p>
038 * If we create a child and its complement we preserving the total number of
039 * genes in the population, preventing any genetic drift.
040 * Single-point crossover is the classic form of crossover. However, it produces
041 * very slow mixing compared with multi-point crossover or uniform crossover.
042 * For problems where the site position has some intrinsic meaning to the
043 * problem single-point crossover can lead to small disruption than multi-point
044 * or uniform crossover.
045 *
046 * @see MultiPointCrossover
047 *
048 * @author <a href="mailto:franz.wilhelmstoetter@gmail.com">Franz Wilhelmstötter</a>
049 * @since 1.0
050 * @version 5.0
051 */
052 public class SinglePointCrossover<
053 G extends Gene<?, G>,
054 C extends Comparable<? super C>
055 >
056 extends MultiPointCrossover<G, C>
057 {
058
059 /**
060 * Constructs an alterer with a given recombination probability.
061 *
062 * @param probability the crossover probability.
063 * @throws IllegalArgumentException if the {@code probability} is not in the
064 * valid range of {@code [0, 1]}.
065 */
066 public SinglePointCrossover(final double probability) {
067 super(probability, 1);
068 }
069
070 /**
071 * Create a new single-point crossover object with crossover probability of
072 * {@code 0.05}.
073 */
074 public SinglePointCrossover() {
075 this(0.05);
076 }
077
078 @Override
079 protected int crossover(final MSeq<G> that, final MSeq<G> other) {
080 final var random = RandomRegistry.random();
081
082 final int index = random.nextInt(min(that.length(), other.length()));
083 crossover(that, other, index);
084 return 2;
085 }
086
087 // Package private for testing purpose.
088 static <T> void crossover(
089 final MSeq<T> that,
090 final MSeq<T> other,
091 final int index
092 ) {
093 assert index >= 0 :
094 format(
095 "Crossover index must be within [0, %d) but was %d",
096 that.length(), index
097 );
098
099 that.swap(index, min(that.length(), other.length()), other, index);
100 }
101
102 @Override
103 public String toString() {
104 return format("%s[p=%f]", getClass().getSimpleName(), _probability);
105 }
106
107 }
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