001/*
002 * Java Genetic Algorithm Library (jenetics-8.1.0).
003 * Copyright (c) 2007-2024 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.ext;
021
022import static java.lang.Math.min;
023
024import io.jenetics.Chromosome;
025import io.jenetics.Genotype;
026import io.jenetics.Phenotype;
027import io.jenetics.Recombinator;
028import io.jenetics.util.MSeq;
029import io.jenetics.util.RandomRegistry;
030
031import io.jenetics.ext.util.FlatTree;
032import io.jenetics.ext.util.FlatTreeNode;
033import io.jenetics.ext.util.TreeNode;
034
035/**
036 * Abstract implementation of tree base crossover recombinator. This class
037 * simplifies the implementation of tree base crossover implementation, by doing
038 * the transformation of the flattened tree genes to actual trees and vice versa.
039 * Only the {@link #crossover(TreeNode, TreeNode)} method must be implemented.
040 *
041 * @author <a href="mailto:franz.wilhelmstoetter@gmail.com">Franz Wilhelmstötter</a>
042 * @version 3.9
043 * @since 3.9
044 */
045public abstract class TreeCrossover<
046        G extends TreeGene<?, G>,
047        C extends Comparable<? super C>
048>
049        extends Recombinator<G, C>
050{
051
052        /**
053         * Constructs a tree crossover with a given recombination probability.
054         *
055         * @param probability the recombination probability
056         * @throws IllegalArgumentException if the {@code probability} is not in the
057         *          valid range of {@code [0, 1]}
058         */
059        protected TreeCrossover(final double probability) {
060                super(probability, 2);
061        }
062
063        @Override
064        protected int recombine(
065                final MSeq<Phenotype<G, C>> population,
066                final int[] individuals,
067                final long generation
068        ) {
069                assert individuals.length == 2 : "Required order of 2";
070                final var random = RandomRegistry.random();
071
072                final Phenotype<G, C> pt1 = population.get(individuals[0]);
073                final Phenotype<G, C> pt2 = population.get(individuals[1]);
074                final Genotype<G> gt1 = pt1.genotype();
075                final Genotype<G> gt2 = pt2.genotype();
076
077                //Choosing the Chromosome index for crossover.
078                final int chIndex = random.nextInt(min(gt1.length(), gt2.length()));
079
080                final MSeq<Chromosome<G>> c1 = MSeq.of(gt1);
081                final MSeq<Chromosome<G>> c2 = MSeq.of(gt2);
082
083                crossover(c1, c2, chIndex);
084
085                //Creating two new Phenotypes and exchanging it with the old.
086                population.set(
087                        individuals[0],
088                        Phenotype.of(Genotype.of(c1.toISeq()), generation)
089                );
090                population.set(
091                        individuals[1],
092                        Phenotype.of(Genotype.of(c2.toISeq()), generation)
093                );
094
095                return order();
096        }
097
098        // Since the allele type "A" is not part of the type signature, we have to
099        // do some unchecked casts to make it "visible" again. The implementor of
100        // the abstract "crossover" method usually doesn't have to do additional casts.
101        private <A> void crossover(
102                final MSeq<Chromosome<G>> c1,
103                final MSeq<Chromosome<G>> c2,
104                final int index
105        ) {
106                @SuppressWarnings("unchecked")
107                final TreeNode<A> tree1 = (TreeNode<A>)TreeNode.ofTree(c1.get(index).gene());
108                @SuppressWarnings("unchecked")
109                final TreeNode<A> tree2 = (TreeNode<A>)TreeNode.ofTree(c2.get(index).gene());
110
111                crossover(tree1, tree2);
112
113                final var flat1 = FlatTreeNode.ofTree(tree1);
114                final var flat2 = FlatTreeNode.ofTree(tree2);
115
116                @SuppressWarnings("unchecked")
117                final var template = (TreeGene<A, ?>)c1.get(0).gene();
118
119                final var genes1 = flat1.map(tree -> gene(template, tree));
120                final var genes2 = flat2.map(tree -> gene(template, tree));
121
122                c1.set(index, c1.get(index).newInstance(genes1));
123                c2.set(index, c2.get(index).newInstance(genes2));
124        }
125
126        @SuppressWarnings("unchecked")
127        private <A> G gene(
128                final TreeGene<A, ?> template,
129                final FlatTree<? extends A, ?> tree
130        ) {
131                return (G)template.newInstance(
132                        tree.value(),
133                        tree.childOffset(),
134                        tree.childCount()
135                );
136        }
137
138        /**
139         * Template method which performs the crossover. The arguments given are
140         * mutable non-null trees.
141         *
142         * @param <A> the <em>existential</em> allele type
143         * @param that the first (chromosome) tree
144         * @param other he second (chromosome) tree
145         * @return the number of altered genes
146         */
147        protected abstract <A> int crossover(
148                final TreeNode<A> that,
149                final TreeNode<A> other
150        );
151
152}