001 /*
002 * Java Genetic Algorithm Library (jenetics-4.0.0).
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@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 io.jenetics.internal.math.base.clamp;
025
026 import java.util.Random;
027
028 import io.jenetics.Crossover;
029 import io.jenetics.NumericGene;
030 import io.jenetics.internal.math.random;
031 import io.jenetics.internal.util.require;
032 import io.jenetics.util.MSeq;
033 import io.jenetics.util.RandomRegistry;
034
035 /**
036 * Performs the simulated binary crossover (SBX) on a {@code Chromosome} of
037 * {@link NumericGene}s such that each position is either crossed contracted or
038 * expanded with a certain probability. The probability distribution is designed
039 * such that the children will lie closer to their parents as is the case with
040 * the single point binary crossover.
041 * <p>
042 * It is implemented as described in Deb, K. and Agrawal, R. B. 1995. Simulated
043 * binary crossover for continuous search space. Complex Systems, 9, pp. 115-148.
044 *
045 * @author <a href="mailto:franz.wilhelmstoetter@gmail.com">Franz Wilhelmstötter</a>
046 * @since 3.5
047 * @version 3.5
048 */
049 public class SimulatedBinaryCrossover<
050 G extends NumericGene<?, G>,
051 C extends Comparable<? super C>
052 >
053 extends Crossover<G, C>
054 {
055 private final double _contiguity;
056
057 /**
058 * Create a new <i>simulated binary crossover</i> alterer with the given
059 * parameters.
060 *
061 * @param probability the recombination probability
062 * @param contiguity the contiguity value that specifies how close a child
063 * should be to its parents (larger value means closer). The value
064 * must be greater or equal than 0. Typical values are in the range
065 * [2..5].
066 * @throws IllegalArgumentException if the {@code probability} is not in the
067 * valid range of {@code [0, 1]}
068 * @throws IllegalArgumentException if {@code contiguity} is smaller than
069 * zero
070 */
071 public SimulatedBinaryCrossover(
072 final double probability,
073 final double contiguity
074 ) {
075 super(probability);
076 _contiguity = require.nonNegative(contiguity);
077 }
078
079 /**
080 * Create a new <i>simulated binary crossover</i> alterer with the given
081 * parameters. The <i>contiguity</i> value is set to {@code 2.5}.
082 *
083 * @param probability the recombination probability
084 * @throws IllegalArgumentException if the {@code probability} is not in the
085 * valid range of {@code [0, 1]}
086 * @throws IllegalArgumentException if {@code contiguity} is smaller than
087 * zero
088 */
089 public SimulatedBinaryCrossover(final double probability) {
090 this(probability, 2.5);
091 }
092
093 /**
094 * Return the <i>contiguity</i> value of the crossover.
095 *
096 * @return the <i>contiguity</i> value of the crossover
097 */
098 public double getContiguity() {
099 return _contiguity;
100 }
101
102 @Override
103 protected int crossover(final MSeq<G> that, final MSeq<G> other) {
104 return (int)random.indexes(RandomRegistry.getRandom(), that.length(), 0.5)
105 .peek(i -> crossover(that, other, i))
106 .count();
107 }
108
109 private void crossover(final MSeq<G> that, final MSeq<G> other, final int i) {
110 final Random random = RandomRegistry.getRandom();
111
112 final double u = random.nextDouble();
113 final double beta;
114 if (u < 0.5) {
115 // If u is smaller than 0.5 perform a contracting crossover.
116 beta = pow(2*u, 1.0/(_contiguity + 1));
117 } else if (u > 0.5) {
118 // Otherwise perform an expanding crossover.
119 beta = pow(0.5 / (1.0 - u), 1.0/(_contiguity + 1));
120 } else if (u == 0.5) {
121 beta = 1;
122 } else {
123 beta = 0;
124 }
125
126 final double v1 = that.get(i).doubleValue();
127 final double v2 = other.get(i).doubleValue();
128 final double v = random.nextBoolean()
129 ? ((v1 - v2)*0.5) - beta*0.5*abs(v1 - v2)
130 : ((v1 - v2)*0.5) + beta*0.5*abs(v1 - v2);
131
132 final double min = that.get(i).getMin().doubleValue();
133 final double max = that.get(i).getMax().doubleValue();
134 that.set(i, that.get(i).newInstance(clamp(v, min, max)));
135 }
136
137 }
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