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 org.jenetics.internal.math.random.indexes;
024
025 import org.jenetics.internal.util.require;
026
027 import org.jenetics.util.MSeq;
028 import org.jenetics.util.RandomRegistry;
029
030 /**
031 * The uniform crossover uses swaps single genes between two chromosomes, instead
032 * of whole ranges as in single- and multi-point crossover.
033 * <pre>
034 * +---+---+---+---+---+---+---+
035 * | 1 | 2 | 3 | 4 | 6 | 7 | 8 |
036 * +-+-+---+-+-+-+-+---+-+-+---+
037 * | | | | swapping
038 * +-+-+---+-+-+-+-+---+-+-+---+
039 * | a | b | c | d | e | f | g |
040 * +---+---+---+---+---+---+---+
041 * </pre>
042 * The probability that two genes are swapped is controlled by the
043 * <i>swap-probability</i> ({@link #getSwapProbability()}), whereas the
044 * probability that a given individual is selected for crossover is defined by
045 * the <i>crossover-probability</i> ({@link #getProbability()}).
046 *
047 * @see <a href="https://en.wikipedia.org/wiki/Crossover_(genetic_algorithm)#Uniform_crossover_and_half_uniform_crossover">
048 * Wikipedia: Uniform crossover</a>
049 *
050 * @author <a href="mailto:franz.wilhelmstoetter@gmx.at">Franz Wilhelmstötter</a>
051 * @version 3.7
052 * @since 3.7
053 */
054 public class UniformCrossover<
055 G extends Gene<?, G>,
056 C extends Comparable<? super C>
057 >
058 extends Crossover<G, C>
059 {
060
061 private final double _swapProbability;
062
063 /**
064 * Create a new universal crossover instance.
065 *
066 * @param crossoverProbability the recombination probability as defined in
067 * {@link Crossover#Crossover(double)}. This is the probability that
068 * a given individual is selected for crossover.
069 * @param swapProbability the probability for swapping a given gene of
070 * a chromosome
071 * @throws IllegalArgumentException if the probabilities are not in the
072 * valid range of {@code [0, 1]}
073 */
074 public UniformCrossover(
075 final double crossoverProbability,
076 final double swapProbability
077 ) {
078 super(crossoverProbability);
079 _swapProbability = require.probability(swapProbability);
080 }
081
082 /**
083 * Create a new universal crossover instance. The {@code swapProbability} is
084 * set to {@link Alterer#DEFAULT_ALTER_PROBABILITY}.
085 *
086 * @param crossoverProbability the recombination probability as defined in
087 * {@link Crossover#Crossover(double)}. This is the probability that
088 * a given individual is selected for crossover.
089 * @throws IllegalArgumentException if the probabilities are not in the
090 * valid range of {@code [0, 1]}
091 */
092 public UniformCrossover(final double crossoverProbability) {
093 this(crossoverProbability, DEFAULT_ALTER_PROBABILITY);
094 }
095
096 /**
097 * Create a new universal crossover instance. The probabilities are set to
098 * {@link Alterer#DEFAULT_ALTER_PROBABILITY}.
099 */
100 public UniformCrossover() {
101 this(DEFAULT_ALTER_PROBABILITY, DEFAULT_ALTER_PROBABILITY);
102 }
103
104 /**
105 * Return the probability for swapping genes of a chromosome.
106 *
107 * @return the probability for swapping genes of a chromosome
108 */
109 public double getSwapProbability() {
110 return _swapProbability;
111 }
112
113 @Override
114 protected int crossover(final MSeq<G> that, final MSeq<G> other) {
115 final int length = min(that.length(), other.length());
116 return (int)indexes(RandomRegistry.getRandom(), length, _swapProbability)
117 .peek(i -> swap(i, that, other))
118 .count();
119 }
120
121 private static <T> void swap(
122 final int index,
123 final MSeq<T> that,
124 final MSeq<T> other
125 ) {
126 final T temp = that.get(index);
127 that.set(index, other.get(index));
128 other.set(index, temp);
129 }
130
131 }
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