001 /*
002 * Java Genetic Algorithm Library (jenetics-4.3.0).
003 * Copyright (c) 2007-2018 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 java.util.Random;
026
027 import io.jenetics.util.MSeq;
028 import io.jenetics.util.RandomRegistry;
029
030 /**
031 * <strong>Single point crossover</strong>
032 *
033 * <p>
034 * One or two children are created by taking two parent strings and cutting
035 * them at some randomly chosen site. E.g.
036 * <p>
037 * <img src="doc-files/SinglePointCrossover.svg" width="400"
038 * alt="Single-point crossover" >
039 * <p>
040 * If we create a child and its complement we preserving the total number of
041 * genes in the population, preventing any genetic drift.
042 * Single-point crossover is the classic form of crossover. However, it produces
043 * very slow mixing compared with multi-point crossover or uniform crossover.
044 * For problems where the site position has some intrinsic meaning to the
045 * problem single-point crossover can lead to small disruption than multi-point
046 * or uniform crossover.
047 *
048 * @see MultiPointCrossover
049 *
050 * @author <a href="mailto:franz.wilhelmstoetter@gmail.com">Franz Wilhelmstötter</a>
051 * @since 1.0
052 * @version 4.0
053 */
054 public class SinglePointCrossover<
055 G extends Gene<?, G>,
056 C extends Comparable<? super C>
057 >
058 extends MultiPointCrossover<G, C>
059 {
060
061 /**
062 * Constructs an alterer with a given recombination probability.
063 *
064 * @param probability the crossover probability.
065 * @throws IllegalArgumentException if the {@code probability} is not in the
066 * valid range of {@code [0, 1]}.
067 */
068 public SinglePointCrossover(final double probability) {
069 super(probability, 1);
070 }
071
072 /**
073 * Create a new single point crossover object with crossover probability of
074 * {@code 0.05}.
075 */
076 public SinglePointCrossover() {
077 this(0.05);
078 }
079
080 @Override
081 protected int crossover(final MSeq<G> that, final MSeq<G> other) {
082 final Random random = RandomRegistry.getRandom();
083
084 final int index = random.nextInt(min(that.length(), other.length()));
085 crossover(that, other, index);
086 return 2;
087 }
088
089 // Package private for testing purpose.
090 static <T> void crossover(
091 final MSeq<T> that,
092 final MSeq<T> other,
093 final int index
094 ) {
095 assert index >= 0 :
096 format(
097 "Crossover index must be within [0, %d) but was %d",
098 that.length(), index
099 );
100
101 that.swap(index, min(that.length(), other.length()), other, index);
102 }
103
104 @Override
105 public String toString() {
106 return format("%s[p=%f]", getClass().getSimpleName(), _probability);
107 }
108
109 }
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