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 io.jenetics.Gene;
025 import io.jenetics.Mutator;
026 import io.jenetics.TruncationSelector;
027 import io.jenetics.engine.Engine.Builder;
028 import io.jenetics.engine.Engine.Setup;
029 import io.jenetics.internal.util.Requires;
030
031 /**
032 * Setup for a (μ, λ)-Evolution Strategy. Applying this setup is done in the
033 * following way.
034 * <pre>{@code
035 * final var engine = Engine.builder(problem)
036 * .setup(new MLEvolutionStrategy<>(μ, λ, p)
037 * .build();
038 * }</pre>
039 *
040 * And is equivalent to the following builder setup.
041 * <pre>{@code
042 * final var engine = Engine.builder(problem)
043 * .populationSize(λ)
044 * .survivorsSize(0)
045 * .offspringSelector(new TruncationSelector<>(μ))
046 * .alterers(new Mutator<>(p))
047 * .build();
048 * }</pre>
049 *
050 * @param <G> the gene type
051 * @param <C> the fitness result type
052 *
053 * @author <a href="mailto:franz.wilhelmstoetter@gmail.com">Franz Wilhelmstötter</a>
054 * @version 6.0
055 * @since 6.0
056 */
057 public final class MLEvolutionStrategy<
058 G extends Gene<?, G>,
059 C extends Comparable<? super C>
060 >
061 implements Setup<G, C>
062 {
063
064 private final int _mu;
065 private final int _lambda;
066 private final double _mutationProbability;
067
068 /**
069 * Create a new (μ, λ)-Evolution Strategy with the given parameters.
070 *
071 * @param mu the number of fittest individuals to be selected
072 * @param lambda the population count
073 * @param mutationProbability the mutation probability
074 * @throws IllegalArgumentException if {@code mu < 2} or {@code lambda < mu}
075 * or {@code mutationProbability not in [0, 1]}
076 */
077 public MLEvolutionStrategy(
078 final int mu,
079 final int lambda,
080 final double mutationProbability
081 ) {
082 if (mu < 2) {
083 throw new IllegalArgumentException(format(
084 "mu (μ) must be greater or equal 2: %d.", mu
085 ));
086 }
087 if (lambda < mu) {
088 throw new IllegalArgumentException(format(
089 "lambda (λ) must be greater or equal then μ [μ=%d, λ=%d].",
090 mu, lambda
091 ));
092 }
093
094 _mu = mu;
095 _lambda = lambda;
096 _mutationProbability = Requires.probability(mutationProbability);
097 }
098
099 /**
100 * Create a new (μ, λ)-Evolution Strategy with the given parameters. The
101 * mutation probability is set to {@link Mutator#DEFAULT_ALTER_PROBABILITY}.
102 *
103 * @param mu the number of fittest individuals to be selected
104 * @param lambda the population count
105 * @throws IllegalArgumentException if {@code mu < 2} or {@code lambda < mu}
106 * or {@code mutationProbability not in [0, 1]}
107 */
108 public MLEvolutionStrategy(final int mu, final int lambda) {
109 this(mu, lambda, Mutator.DEFAULT_ALTER_PROBABILITY);
110 }
111
112 @Override
113 public void apply(final Builder<G, C> builder) {
114 builder.populationSize(_lambda)
115 .survivorsSize(0)
116 .offspringSelector(new TruncationSelector<>(_mu))
117 .alterers(new Mutator<>(_mutationProbability));
118 }
119
120 }
|