001/*
002 * Java Genetic Algorithm Library (jenetics-7.1.0).
003 * Copyright (c) 2007-2022 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 */
020package io.jenetics;
021
022import static java.lang.Math.min;
023import static java.lang.String.format;
024import static java.util.Objects.requireNonNull;
025
026import java.util.function.BinaryOperator;
027
028import io.jenetics.util.BaseSeq;
029import io.jenetics.util.MSeq;
030import io.jenetics.util.RandomRegistry;
031
032/**
033 * Alters a chromosome by replacing two genes by the result of a given
034 * <em>combiner</em> function.
035 *
036 * <p>
037 * The order ({@link #order()}) of this recombination implementation is two.
038 * </p>
039 *
040 * @author <a href="mailto:franz.wilhelmstoetter@gmail.com">Franz Wilhelmstötter</a>
041 * @since 6.0
042 * @version 6.0
043 */
044public class CombineAlterer<
045        G extends Gene<?, G>,
046        C extends Comparable<? super C>
047>
048        extends Recombinator<G, C>
049{
050
051        private final BinaryOperator<G> _combiner;
052
053        /**
054         * Create a new combiner alterer with the given arguments.
055         *
056         * @param combiner the function used for combining two genes
057         * @param probability The recombination probability.
058         * @throws IllegalArgumentException if the {@code probability} is not in the
059         *         valid range of {@code [0, 1]}
060         * @throws NullPointerException if the given {@code combiner} is {@code null}
061         */
062        public CombineAlterer(
063                final BinaryOperator<G> combiner,
064                final double probability
065        ) {
066                super(probability, 2);
067                _combiner = requireNonNull(combiner);
068        }
069
070        /**
071         * Create a new combiner alterer with the given arguments.
072         *
073         * @param combiner the function used for combining two genes
074         * @throws IllegalArgumentException if the {@code probability} is not in the
075         *         valid range of {@code [0, 1]}
076         * @throws NullPointerException if the given {@code combiner} is {@code null}
077         */
078        public CombineAlterer(final BinaryOperator<G> combiner) {
079                this(combiner, DEFAULT_ALTER_PROBABILITY);
080        }
081
082        /**
083         * Return the combiner function, used by {@code this} alterer.
084         *
085         * @return the combiner function, used by {@code this} alterer
086         */
087        public BinaryOperator<G> combiner() {
088                return _combiner;
089        }
090
091        @Override
092        protected int recombine(
093                final MSeq<Phenotype<G, C>> population,
094                final int[] individuals,
095                final long generation
096        ) {
097                final Phenotype<G, C> pt1 = population.get(individuals[0]);
098                final Phenotype<G, C> pt2 = population.get(individuals[1]);
099                final Genotype<G> gt1 = pt1.genotype();
100                final Genotype<G> gt2 = pt2.genotype();
101
102                //Choosing the Chromosome index for crossover.
103                final int ci = RandomRegistry.random()
104                        .nextInt(min(gt1.length(), gt2.length()));
105
106                final MSeq<Chromosome<G>> c1 = MSeq.of(gt1);
107
108                // Calculate the mean value of the gene array.
109                final MSeq<G> mean = combine(c1.get(ci), gt2.get(ci), _combiner);
110
111                c1.set(ci, c1.get(ci).newInstance(mean.toISeq()));
112                population.set(individuals[0], Phenotype.of(Genotype.of(c1), generation));
113
114                return 1;
115        }
116
117        private static <G extends Gene<?, G>>
118        MSeq<G> combine(
119                final BaseSeq<G> a,
120                final BaseSeq<G> b,
121                final BinaryOperator<G> combiner
122        ) {
123                final MSeq<G> result = MSeq.ofLength(a.length());
124                for (int i = a.length(); --i >= 0;) {
125                        result.set(i, combiner.apply(a.get(i), b.get(i)));
126                }
127                return result;
128        }
129
130        @Override
131        public String toString() {
132                return format("%s[p=%f]", getClass().getSimpleName(), _probability);
133        }
134}