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.ext;
021
022 import static java.lang.String.format;
023
024 import java.util.Random;
025
026 import io.jenetics.AltererResult;
027 import io.jenetics.Gene;
028 import io.jenetics.Genotype;
029 import io.jenetics.Mutator;
030 import io.jenetics.MutatorResult;
031 import io.jenetics.Phenotype;
032 import io.jenetics.util.ISeq;
033 import io.jenetics.util.RandomRegistry;
034 import io.jenetics.util.Seq;
035
036 /**
037 * Mutator implementation which is part of the
038 * <a href="https://en.wikipedia.org/wiki/Weasel_program">Weasel program</a>
039 * algorithm. The <i>Weasel program</i> is an thought experiment by Richard
040 * Dawkins to illustrate the functioning of the evolution: random <i>mutation</i>
041 * combined with non-random cumulative <i>selection</i>.
042 * <p>
043 * The mutator mutates the genes of <i>every</i> chromosome of <i>every</i>
044 * genotype in the population with the given mutation probability.
045 * </p>
046 * {@link io.jenetics.engine.Engine} setup for the <i>Weasel program:</i>
047 * <pre>{@code
048 * final Engine<CharacterGene, Integer> engine = Engine.builder(problem)
049 * // Set the 'WeaselSelector'.
050 * .selector(new WeaselSelector<>())
051 * // Disable survivors selector.
052 * .offspringFraction(1)
053 * // Set the 'WeaselMutator'.
054 * .alterers(new WeaselMutator<>(0.05))
055 * .build();
056 * }</pre>
057 *
058 * @see <a href="https://en.wikipedia.org/wiki/Weasel_program">Weasel program</a>
059 * @see WeaselSelector
060 *
061 * @param <G> the gene type
062 * @param <C> the fitness result type
063 *
064 * @author <a href="mailto:franz.wilhelmstoetter@gmail.com">Franz Wilhelmstötter</a>
065 * @since 3.5
066 * @version 5.0
067 */
068 public class WeaselMutator<
069 G extends Gene<?, G>,
070 C extends Comparable<? super C>
071 >
072 extends Mutator<G, C>
073 {
074
075 /**
076 * Create a new weasel mutator with the given mutation probability.
077 *
078 * @param probability the mutation probability
079 * @throws IllegalArgumentException if the {@code probability} is not in the
080 * valid range of {@code [0, 1]}.
081 */
082 public WeaselMutator(final double probability) {
083 super(probability);
084 }
085
086 /**
087 * Create a new weasel mutator with the <em>default</em> mutation probability
088 * of {@code 0.05}.
089 */
090 public WeaselMutator() {
091 this(0.05);
092 }
093
094 @Override
095 public AltererResult<G, C>
096 alter(final Seq<Phenotype<G, C>> population, final long generation) {
097 final var random = RandomRegistry.random();
098 final var result = population
099 .map(pt -> mutate(pt, generation, _probability, random));
100
101 return AltererResult.of(
102 result
103 .map(MutatorResult::result)
104 .asISeq(),
105 result.stream()
106 .mapToInt(MutatorResult::mutations)
107 .sum()
108 );
109 }
110
111 @Override
112 protected MutatorResult<Genotype<G>> mutate(
113 final Genotype<G> genotype,
114 final double p,
115 final Random random
116 ) {
117 final var result = genotype.stream()
118 .map(gt -> mutate(gt, p, random))
119 .collect(ISeq.toISeq());
120
121 return MutatorResult.of(
122 Genotype.of(result.map(MutatorResult::result)),
123 result.stream().mapToInt(MutatorResult::mutations).sum()
124 );
125 }
126
127 @Override
128 public String toString() {
129 return format("WeaselMutator[%f]", _probability);
130 }
131
132 }
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