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.min;
023
024 import java.util.Random;
025
026 import io.jenetics.Chromosome;
027 import io.jenetics.Genotype;
028 import io.jenetics.Phenotype;
029 import io.jenetics.Recombinator;
030 import io.jenetics.util.ISeq;
031 import io.jenetics.util.MSeq;
032 import io.jenetics.util.RandomRegistry;
033
034 import io.jenetics.ext.util.FlatTree;
035 import io.jenetics.ext.util.FlatTreeNode;
036 import io.jenetics.ext.util.TreeNode;
037
038 /**
039 * Abstract implementation of tree base crossover recombinator. This class
040 * simplifies the implementation of tree base crossover implementation, by doing
041 * the transformation of the flattened tree genes to actual trees and vice versa.
042 * Only the {@link #crossover(TreeNode, TreeNode)} method must be implemented.
043 *
044 * @author <a href="mailto:franz.wilhelmstoetter@gmail.com">Franz Wilhelmstötter</a>
045 * @version 3.9
046 * @since 3.9
047 */
048 public abstract class TreeCrossover<
049 G extends TreeGene<?, G>,
050 C extends Comparable<? super C>
051 >
052 extends Recombinator<G, C>
053 {
054
055 /**
056 * Constructs an tree crossover with a given recombination probability.
057 *
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 */
062 protected TreeCrossover(final double probability) {
063 super(probability, 2);
064 }
065
066 @Override
067 protected int recombine(
068 final MSeq<Phenotype<G, C>> population,
069 final int[] individuals,
070 final long generation
071 ) {
072 assert individuals.length == 2 : "Required order of 2";
073 final Random random = RandomRegistry.getRandom();
074
075 final Phenotype<G, C> pt1 = population.get(individuals[0]);
076 final Phenotype<G, C> pt2 = population.get(individuals[1]);
077 final Genotype<G> gt1 = pt1.getGenotype();
078 final Genotype<G> gt2 = pt2.getGenotype();
079
080 //Choosing the Chromosome index for crossover.
081 final int chIndex = random.nextInt(min(gt1.length(), gt2.length()));
082
083 final MSeq<Chromosome<G>> c1 = gt1.toSeq().copy();
084 final MSeq<Chromosome<G>> c2 = gt2.toSeq().copy();
085
086 crossover(c1, c2, chIndex);
087
088 //Creating two new Phenotypes and exchanging it with the old.
089 population.set(
090 individuals[0],
091 pt1.newInstance(Genotype.of(c1.toISeq()), generation)
092 );
093 population.set(
094 individuals[1],
095 pt2.newInstance(Genotype.of(c2.toISeq()), generation)
096 );
097
098 return getOrder();
099 }
100
101 // Since the allele type "A" is not part of the type signature, we have to
102 // do some unchecked casts to make it "visible" again. The implementor of
103 // the abstract "crossover" method usually don't have to do additional casts.
104 private <A> void crossover(
105 final MSeq<Chromosome<G>> c1,
106 final MSeq<Chromosome<G>> c2,
107 final int index
108 ) {
109 @SuppressWarnings("unchecked")
110 final TreeNode<A> tree1 = (TreeNode<A>)TreeNode.ofTree(c1.get(index).getGene());
111 @SuppressWarnings("unchecked")
112 final TreeNode<A> tree2 = (TreeNode<A>)TreeNode.ofTree(c2.get(index).getGene());
113
114 crossover(tree1, tree2);
115
116 final FlatTreeNode<A> flat1 = FlatTreeNode.of(tree1);
117 final FlatTreeNode<A> flat2 = FlatTreeNode.of(tree2);
118
119 @SuppressWarnings("unchecked")
120 final TreeGene<A, ?> template = (TreeGene<A, ?>)c1.get(0).getGene();
121
122 final ISeq<G> genes1 = flat1.map(tree -> gene(template, tree));
123 final ISeq<G> genes2 = flat2.map(tree -> gene(template, tree));
124
125 c1.set(index, c1.get(index).newInstance(genes1));
126 c2.set(index, c2.get(index).newInstance(genes2));
127 }
128
129 @SuppressWarnings("unchecked")
130 private <A> G gene(
131 final TreeGene<A, ?> template,
132 final FlatTree<? extends A, ?> tree
133 ) {
134 return (G)template.newInstance(
135 tree.getValue(),
136 tree.childOffset(),
137 tree.childCount()
138 );
139 }
140
141 /**
142 * Template method which performs the crossover. The arguments given are
143 * mutable non null trees.
144 *
145 * @param <A> the <em>existential</em> allele type
146 * @param that the first (chromosome) tree
147 * @param other he second (chromosome) tree
148 * @return the number of altered genes
149 */
150 protected abstract <A> int crossover(
151 final TreeNode<A> that,
152 final TreeNode<A> other
153 );
154
155 }
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