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.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 import static io.jenetics.internal.util.Hashes.hash;
027
028 import java.util.Random;
029
030 import io.jenetics.Crossover;
031 import io.jenetics.NumericGene;
032 import io.jenetics.internal.math.random;
033 import io.jenetics.internal.util.require;
034 import io.jenetics.util.MSeq;
035 import io.jenetics.util.RandomRegistry;
036
037 /**
038 * Performs the simulated binary crossover (SBX) on a {@code Chromosome} of
039 * {@link NumericGene}s such that each position is either crossed contracted or
040 * expanded with a certain probability. The probability distribution is designed
041 * such that the children will lie closer to their parents as is the case with
042 * the single point binary crossover.
043 * <p>
044 * It is implemented as described in Deb, K. and Agrawal, R. B. 1995. Simulated
045 * binary crossover for continuous search space. Complex Systems, 9, pp. 115-148.
046 *
047 * @author <a href="mailto:franz.wilhelmstoetter@gmail.com">Franz Wilhelmstötter</a>
048 * @since 3.5
049 * @version 3.5
050 */
051 public class SimulatedBinaryCrossover<
052 G extends NumericGene<?, G>,
053 C extends Comparable<? super C>
054 >
055 extends Crossover<G, C>
056 {
057 private final double _contiguity;
058
059 /**
060 * Create a new <i>simulated binary crossover</i> alterer with the given
061 * parameters.
062 *
063 * @param probability the recombination probability
064 * @param contiguity the contiguity value that specifies how close a child
065 * should be to its parents (larger value means closer). The value
066 * must be greater or equal than 0. Typical values are in the range
067 * [2..5].
068 * @throws IllegalArgumentException if the {@code probability} is not in the
069 * valid range of {@code [0, 1]}
070 * @throws IllegalArgumentException if {@code contiguity} is smaller than
071 * zero
072 */
073 public SimulatedBinaryCrossover(
074 final double probability,
075 final double contiguity
076 ) {
077 super(probability);
078 _contiguity = require.nonNegative(contiguity);
079 }
080
081 /**
082 * Create a new <i>simulated binary crossover</i> alterer with the given
083 * parameters. The <i>contiguity</i> value is set to {@code 2.5}.
084 *
085 * @param probability the recombination probability
086 * @throws IllegalArgumentException if the {@code probability} is not in the
087 * valid range of {@code [0, 1]}
088 * @throws IllegalArgumentException if {@code contiguity} is smaller than
089 * zero
090 */
091 public SimulatedBinaryCrossover(final double probability) {
092 this(probability, 2.5);
093 }
094
095 /**
096 * Return the <i>contiguity</i> value of the crossover.
097 *
098 * @return the <i>contiguity</i> value of the crossover
099 */
100 public double getContiguity() {
101 return _contiguity;
102 }
103
104 @Override
105 protected int crossover(final MSeq<G> that, final MSeq<G> other) {
106 return (int)random.indexes(RandomRegistry.getRandom(), that.length(), 0.5)
107 .peek(i -> crossover(that, other, i))
108 .count();
109 }
110
111 private void crossover(final MSeq<G> that, final MSeq<G> other, final int i) {
112 final Random random = RandomRegistry.getRandom();
113
114 final double u = random.nextDouble();
115 final double beta;
116 if (u < 0.5) {
117 // If u is smaller than 0.5 perform a contracting crossover.
118 beta = pow(2*u, 1.0/(_contiguity + 1));
119 } else if (u > 0.5) {
120 // Otherwise perform an expanding crossover.
121 beta = pow(0.5 / (1.0 - u), 1.0/(_contiguity + 1));
122 } else if (u == 0.5) {
123 beta = 1;
124 } else {
125 beta = 0;
126 }
127
128 final double v1 = that.get(i).doubleValue();
129 final double v2 = other.get(i).doubleValue();
130 final double v = random.nextBoolean()
131 ? ((v1 - v2)*0.5) - beta*0.5*abs(v1 - v2)
132 : ((v1 - v2)*0.5) + beta*0.5*abs(v1 - v2);
133
134 final double min = that.get(i).getMin().doubleValue();
135 final double max = that.get(i).getMax().doubleValue();
136 that.set(i, that.get(i).newInstance(clamp(v, min, max)));
137 }
138
139 @Override
140 public int hashCode() {
141 return hash(_probability, hash(_contiguity));
142 }
143
144 @Override
145 public boolean equals(final Object obj) {
146 return obj == this ||
147 obj instanceof SimulatedBinaryCrossover &&
148 Double.compare(((SimulatedBinaryCrossover)obj)._probability, _probability) == 0 &&
149 Double.compare(((SimulatedBinaryCrossover)obj)._contiguity, _contiguity) == 0;
150 }
151
152 @Override
153 public String toString() {
154 return format(
155 "SimulatedBinaryCrossover[p=%f, c=%f]",
156 _probability, _contiguity
157 );
158 }
159
160 }
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