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;
021
022 import static java.util.Objects.requireNonNull;
023
024 import io.jenetics.util.ISeq;
025 import io.jenetics.util.Seq;
026
027 /**
028 * The Alterer is responsible for the changing/recombining the Population.
029 * Alterers can be chained by appending a list of alterers with the
030 * {@link io.jenetics.engine.Engine.Builder#alterers(Alterer, Alterer[])} method.
031 *
032 * <pre>{@code
033 * final Engine<DoubleGene, Double> engine = Engine
034 * .builder(gtf, ff)
035 * .alterers(
036 * new Crossover<>(0.1),
037 * new Mutator<>(0.05),
038 * new MeanAlterer<>(0.2))
039 * .build();
040 * final EvolutionStream<DoubleGene, Double> stream = engine.stream();
041 * }</pre>
042 *
043 * The order of the alterer calls is: Crossover, Mutation and MeanAlterer.
044 *
045 * @param <G> the gene type
046 * @param <C> the fitness function result type
047 *
048 * @author <a href="mailto:franz.wilhelmstoetter@gmail.com">Franz Wilhelmstötter</a>
049 * @since 1.0
050 * @version 4.0
051 */
052 @FunctionalInterface
053 public interface Alterer<
054 G extends Gene<?, G>,
055 C extends Comparable<? super C>
056 > {
057
058 /**
059 * The default alter probability: 0.2
060 */
061 double DEFAULT_ALTER_PROBABILITY = 0.2;
062
063 /**
064 * Alters (recombine) a given population. If the {@code population} is empty,
065 * nothing is altered. The altered population is part of the returned
066 * {@code AlterResult} object.
067 *
068 * @param population The Population to be altered. If the {@code population}
069 * is {@code null} or empty, nothing is altered.
070 * @param generation the date of birth (generation) of the altered phenotypes.
071 * @return the alter-result object, which contains the altered population
072 * and the alteration count
073 * @throws NullPointerException if the given {@code population} is
074 * {@code null}.
075 */
076 AltererResult<G, C> alter(
077 final Seq<Phenotype<G, C>> population,
078 final long generation
079 );
080
081 /**
082 * Returns a composed alterer that first applies the {@code before} alterer
083 * to its input, and then applies {@code this} alterer to the result.
084 *
085 * @param before the alterer to apply first
086 * @return the new composed alterer
087 */
088 default Alterer<G, C> compose(final Alterer<G, C> before) {
089 return of(requireNonNull(before), this);
090 }
091
092 /**
093 * Returns a composed alterer that applies the {@code this} alterer
094 * to its input, and then applies the {@code after} alterer to the result.
095 *
096 * @param after the alterer to apply first
097 * @return the new composed alterer
098 */
099 default Alterer<G, C> andThen(final Alterer<G, C> after) {
100 return of(this, requireNonNull(after));
101 }
102
103 /**
104 * Combine the given alterers.
105 *
106 * @param <G> the gene type
107 * @param <C> the fitness function result type
108 * @param alterers the alterers to combine.
109 * @return a new alterer which consists of the given one
110 * @throws NullPointerException if one of the alterers is {@code null}.
111 */
112 @SafeVarargs
113 static <G extends Gene<?, G>, C extends Comparable<? super C>>
114 Alterer<G, C> of(final Alterer<G, C>... alterers) {
115 return alterers.length == 0
116 ? (p, g) -> AltererResult.of(p.asISeq())
117 : alterers.length == 1
118 ? alterers[0]
119 : new CompositeAlterer<>(ISeq.of(alterers));
120 }
121
122 }
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