001 /*
002 * Java Genetic Algorithm Library (jenetics-6.3.0).
003 * Copyright (c) 2007-2021 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;
021
022 import static java.lang.Math.min;
023 import static java.lang.String.format;
024 import static java.util.Objects.requireNonNull;
025
026 import java.util.Random;
027 import java.util.function.BinaryOperator;
028
029 import io.jenetics.util.BaseSeq;
030 import io.jenetics.util.MSeq;
031 import io.jenetics.util.RandomRegistry;
032
033 /**
034 * Alters a chromosome by replacing two genes by the result of a given
035 * <em>combiner</em> function.
036 *
037 * <p>
038 * The order ({@link #order()}) of this recombination implementation is two.
039 * </p>
040 *
041 * @author <a href="mailto:franz.wilhelmstoetter@gmail.com">Franz Wilhelmstötter</a>
042 * @since 6.0
043 * @version 6.0
044 */
045 public class CombineAlterer<
046 G extends Gene<?, G>,
047 C extends Comparable<? super C>
048 >
049 extends Recombinator<G, C>
050 {
051
052 private final BinaryOperator<G> _combiner;
053
054 /**
055 * Create a new combiner alterer with the given arguments.
056 *
057 * @param combiner the function used for combining two genes
058 * @param probability The recombination probability.
059 * @throws IllegalArgumentException if the {@code probability} is not in the
060 * valid range of {@code [0, 1]}
061 * @throws NullPointerException if the given {@code combiner} is {@code null}
062 */
063 public CombineAlterer(
064 final BinaryOperator<G> combiner,
065 final double probability
066 ) {
067 super(probability, 2);
068 _combiner = requireNonNull(combiner);
069 }
070
071 /**
072 * Create a new combiner alterer with the given arguments.
073 *
074 * @param combiner the function used for combining two genes
075 * @throws IllegalArgumentException if the {@code probability} is not in the
076 * valid range of {@code [0, 1]}
077 * @throws NullPointerException if the given {@code combiner} is {@code null}
078 */
079 public CombineAlterer(final BinaryOperator<G> combiner) {
080 this(combiner, DEFAULT_ALTER_PROBABILITY);
081 }
082
083 /**
084 * Return the combiner function, used by {@code this} alterer.
085 *
086 * @return the combiner function, used by {@code this} alterer
087 */
088 public BinaryOperator<G> combiner() {
089 return _combiner;
090 }
091
092 @Override
093 protected int recombine(
094 final MSeq<Phenotype<G, C>> population,
095 final int[] individuals,
096 final long generation
097 ) {
098 final Random random = RandomRegistry.random();
099
100 final Phenotype<G, C> pt1 = population.get(individuals[0]);
101 final Phenotype<G, C> pt2 = population.get(individuals[1]);
102 final Genotype<G> gt1 = pt1.genotype();
103 final Genotype<G> gt2 = pt2.genotype();
104
105 //Choosing the Chromosome index for crossover.
106 final int ci = random.nextInt(min(gt1.length(), gt2.length()));
107
108 final MSeq<Chromosome<G>> c1 = MSeq.of(gt1);
109
110 // Calculate the mean value of the gene array.
111 final MSeq<G> mean = combine(c1.get(ci), gt2.get(ci), _combiner);
112
113 c1.set(ci, c1.get(ci).newInstance(mean.toISeq()));
114 population.set(individuals[0], Phenotype.of(Genotype.of(c1), generation));
115
116 return 1;
117 }
118
119 private static <G extends Gene<?, G>>
120 MSeq<G> combine(
121 final BaseSeq<G> a,
122 final BaseSeq<G> b,
123 final BinaryOperator<G> combiner
124 ) {
125 final MSeq<G> result = MSeq.ofLength(a.length());
126 for (int i = a.length(); --i >= 0;) {
127 result.set(i, combiner.apply(a.get(i), b.get(i)));
128 }
129 return result;
130 }
131
132 @Override
133 public String toString() {
134 return format("%s[p=%f]", getClass().getSimpleName(), _probability);
135 }
136 }
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