001 /*
002 * Java Genetic Algorithm Library (jenetics-5.1.0).
003 * Copyright (c) 2007-2019 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.base.clamp;
026
027 import java.util.Random;
028
029 import io.jenetics.Crossover;
030 import io.jenetics.NumericGene;
031 import io.jenetics.internal.math.random;
032 import io.jenetics.internal.util.require;
033 import io.jenetics.util.MSeq;
034 import io.jenetics.util.RandomRegistry;
035
036 /**
037 * Performs the simulated binary crossover (SBX) on a {@code Chromosome} of
038 * {@link NumericGene}s such that each position is either crossed contracted or
039 * expanded with a certain probability. The probability distribution is designed
040 * such that the children will lie closer to their parents as is the case with
041 * the single point binary crossover.
042 * <p>
043 * It is implemented as described in Deb, K. and Agrawal, R. B. 1995. Simulated
044 * binary crossover for continuous search space. Complex Systems, 9, pp. 115-148.
045 *
046 * @author <a href="mailto:franz.wilhelmstoetter@gmail.com">Franz Wilhelmstötter</a>
047 * @since 3.5
048 * @version 5.0
049 */
050 public class SimulatedBinaryCrossover<
051 G extends NumericGene<?, G>,
052 C extends Comparable<? super C>
053 >
054 extends Crossover<G, C>
055 {
056 private final double _contiguity;
057
058 /**
059 * Create a new <i>simulated binary crossover</i> alterer with the given
060 * parameters.
061 *
062 * @param probability the recombination probability
063 * @param contiguity the contiguity value that specifies how close a child
064 * should be to its parents (larger value means closer). The value
065 * must be greater or equal than 0. Typical values are in the range
066 * [2..5].
067 * @throws IllegalArgumentException if the {@code probability} is not in the
068 * valid range of {@code [0, 1]}
069 * @throws IllegalArgumentException if {@code contiguity} is smaller than
070 * zero
071 */
072 public SimulatedBinaryCrossover(
073 final double probability,
074 final double contiguity
075 ) {
076 super(probability);
077 _contiguity = require.nonNegative(contiguity);
078 }
079
080 /**
081 * Create a new <i>simulated binary crossover</i> alterer with the given
082 * parameters. The <i>contiguity</i> value is set to {@code 2.5}.
083 *
084 * @param probability the recombination probability
085 * @throws IllegalArgumentException if the {@code probability} is not in the
086 * valid range of {@code [0, 1]}
087 * @throws IllegalArgumentException if {@code contiguity} is smaller than
088 * zero
089 */
090 public SimulatedBinaryCrossover(final double probability) {
091 this(probability, 2.5);
092 }
093
094 /**
095 * Return the <i>contiguity</i> value of the crossover.
096 *
097 * @return the <i>contiguity</i> value of the crossover
098 */
099 public double getContiguity() {
100 return _contiguity;
101 }
102
103 @Override
104 protected int crossover(final MSeq<G> that, final MSeq<G> other) {
105 return (int)random.indexes(RandomRegistry.getRandom(), that.length(), 0.5)
106 .peek(i -> crossover(that, other, i))
107 .count();
108 }
109
110 private void crossover(final MSeq<G> that, final MSeq<G> other, final int i) {
111 final Random random = RandomRegistry.getRandom();
112
113 final double u = random.nextDouble();
114 final double beta;
115 if (u < 0.5) {
116 // If u is smaller than 0.5 perform a contracting crossover.
117 beta = pow(2*u, 1.0/(_contiguity + 1));
118 } else if (u > 0.5) {
119 // Otherwise perform an expanding crossover.
120 beta = pow(0.5 / (1.0 - u), 1.0/(_contiguity + 1));
121 } else if (u == 0.5) {
122 beta = 1;
123 } else {
124 beta = 0;
125 }
126
127 final double v1 = that.get(i).doubleValue();
128 final double v2 = other.get(i).doubleValue();
129 final double v = random.nextBoolean()
130 ? ((v1 - v2)*0.5) - beta*0.5*abs(v1 - v2)
131 : ((v1 - v2)*0.5) + beta*0.5*abs(v1 - v2);
132
133 final double min = that.get(i).getMin().doubleValue();
134 final double max = that.get(i).getMax().doubleValue();
135 that.set(i, that.get(i).newInstance(clamp(v, min, max)));
136 }
137
138 @Override
139 public String toString() {
140 return format(
141 "SimulatedBinaryCrossover[p=%f, c=%f]",
142 _probability, _contiguity
143 );
144 }
145
146 }
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