001 /*
002 * Java Genetic Algorithm Library (jenetics-7.1.2).
003 * Copyright (c) 2007-2023 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.min;
023
024 import io.jenetics.Chromosome;
025 import io.jenetics.Genotype;
026 import io.jenetics.Phenotype;
027 import io.jenetics.Recombinator;
028 import io.jenetics.util.MSeq;
029 import io.jenetics.util.RandomRegistry;
030
031 import io.jenetics.ext.util.FlatTree;
032 import io.jenetics.ext.util.FlatTreeNode;
033 import 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 */
045 public 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 don'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 }
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