001 /*
002 * Java Genetic Algorithm Library (jenetics-7.1.2).
003 * Copyright (c) 2007-2023 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.ext;
021
022 import static java.lang.Math.abs;
023 import static java.lang.Math.pow;
024 import static java.lang.String.format;
025 import static io.jenetics.internal.math.Basics.clamp;
026
027 import io.jenetics.Crossover;
028 import io.jenetics.NumericGene;
029 import io.jenetics.internal.math.Randoms;
030 import io.jenetics.internal.util.Requires;
031 import io.jenetics.util.MSeq;
032 import io.jenetics.util.RandomRegistry;
033
034 /**
035 * Performs the simulated binary crossover (SBX) on a {@code Chromosome} of
036 * {@link NumericGene}s such that each position is either crossed contracted or
037 * expanded with a certain probability. The probability distribution is designed
038 * such that the children will lie closer to their parents as is the case with
039 * the single point binary crossover.
040 * <p>
041 * It is implemented as described in Deb, K. and Agrawal, R. B. 1995. Simulated
042 * binary crossover for continuous search space. Complex Systems, 9, pp. 115-148.
043 *
044 * @author <a href="mailto:franz.wilhelmstoetter@gmail.com">Franz Wilhelmstötter</a>
045 * @since 3.5
046 * @version 6.0
047 */
048 public class SimulatedBinaryCrossover<
049 G extends NumericGene<?, G>,
050 C extends Comparable<? super C>
051 >
052 extends Crossover<G, C>
053 {
054 private final double _contiguity;
055
056 /**
057 * Create a new <i>simulated binary crossover</i> alterer with the given
058 * parameters.
059 *
060 * @param probability the recombination probability
061 * @param contiguity the contiguity value that specifies how close a child
062 * should be to its parents (larger value means closer). The value
063 * must be greater or equal than 0. Typical values are in the range
064 * [2..5].
065 * @throws IllegalArgumentException if the {@code probability} is not in the
066 * valid range of {@code [0, 1]}
067 * @throws IllegalArgumentException if {@code contiguity} is smaller than
068 * zero
069 */
070 public SimulatedBinaryCrossover(
071 final double probability,
072 final double contiguity
073 ) {
074 super(probability);
075 _contiguity = Requires.nonNegative(contiguity);
076 }
077
078 /**
079 * Create a new <i>simulated binary crossover</i> alterer with the given
080 * parameters. The <i>contiguity</i> value is set to {@code 2.5}.
081 *
082 * @param probability the recombination probability
083 * @throws IllegalArgumentException if the {@code probability} is not in the
084 * valid range of {@code [0, 1]}
085 * @throws IllegalArgumentException if {@code contiguity} is smaller than
086 * zero
087 */
088 public SimulatedBinaryCrossover(final double probability) {
089 this(probability, 2.5);
090 }
091
092 /**
093 * Return the <i>contiguity</i> value of the crossover.
094 *
095 * @return the <i>contiguity</i> value of the crossover
096 */
097 public double contiguity() {
098 return _contiguity;
099 }
100
101 @Override
102 protected int crossover(final MSeq<G> that, final MSeq<G> other) {
103 return (int) Randoms.indexes(RandomRegistry.random(), that.length(), 0.5)
104 .peek(i -> crossover(that, other, i))
105 .count();
106 }
107
108 private void crossover(final MSeq<G> that, final MSeq<G> other, final int i) {
109 final var random = RandomRegistry.random();
110
111 final double u = random.nextDouble();
112 final double beta;
113 if (u < 0.5) {
114 // If u is smaller than 0.5 perform a contracting crossover.
115 beta = pow(2*u, 1.0/(_contiguity + 1));
116 } else if (u > 0.5) {
117 // Otherwise, perform an expanding crossover.
118 beta = pow(0.5/(1.0 - u), 1.0/(_contiguity + 1));
119 } else {
120 beta = 1;
121 }
122
123 final double v1 = that.get(i).doubleValue();
124 final double v2 = other.get(i).doubleValue();
125 final double v = random.nextBoolean()
126 ? ((v1 - v2)*0.5) - beta*0.5*abs(v1 - v2)
127 : ((v1 - v2)*0.5) + beta*0.5*abs(v1 - v2);
128
129 final double min = that.get(i).min().doubleValue();
130 final double max = that.get(i).max().doubleValue();
131 that.set(i, that.get(i).newInstance(clamp(v, min, max)));
132 }
133
134 @Override
135 public String toString() {
136 return format(
137 "SimulatedBinaryCrossover[p=%f, c=%f]",
138 _probability, _contiguity
139 );
140 }
141
142 }
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