001 /*
002 * Java Genetic Algorithm Library (jenetics-4.4.0).
003 * Copyright (c) 2007-2019 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.engine;
021
022 import static java.util.Objects.requireNonNull;
023
024 import java.util.function.Function;
025
026 import io.jenetics.Gene;
027 import io.jenetics.Genotype;
028
029 /**
030 * This interface describes a <i>problem</i> which can be solved by the GA
031 * evolution {@code Engine}. It connects the actual {@link #fitness()} function
032 * and the needed {@link #codec()}.
033 *
034 * <pre>{@code
035 * final Problem<ISeq<BitGene>, BitGene, Integer> counting = Problem.of(
036 * // Native fitness function
037 * genes -> (int)genes.stream()
038 * .filter(BitGene::getBit)
039 * .count(),
040 * // Problem encoding
041 * Codec.of(
042 * Genotype.of(BitChromosome.of(100)),
043 * gt -> gt.getChromosome().toSeq()
044 * )
045 * );
046 * }</pre>
047 *
048 * The example above shows the Ones-Counting problem definition.
049 *
050 * @see Codec
051 * @see Engine
052 *
053 * @param <T> the (<i>native</i>) argument type of the problem fitness function
054 * @param <G> the gene type the evolution engine is working with
055 * @param <C> the result type of the fitness function
056 *
057 * @author <a href="mailto:franz.wilhelmstoetter@gmail.com">Franz Wilhelmstötter</a>
058 * @version 4.2
059 * @since 3.4
060 */
061 public interface Problem<
062 T,
063 G extends Gene<?, G>,
064 C extends Comparable<? super C>
065 > {
066
067 /**
068 * Return the fitness function of the <i>problem</i> in the <i>native</i>
069 * problem domain.
070 *
071 * @return the fitness function
072 */
073 public Function<T, C> fitness();
074
075 /**
076 * Return the codec, which translates the types of the problem domain into
077 * types, which can be understand by the evolution {@code Engine}.
078 *
079 * @return the engine codec
080 */
081 public Codec<T, G> codec();
082
083 /**
084 * Converts the given {@link Genotype} to the target type {@link T}. This is
085 * a shortcut for
086 * <pre>{@code
087 * final Problem<SomeObject, DoubleGene, Double> problem = ...
088 * final Genotype<DoubleGene> gt = problem.codec().encoding().newInstance();
089 *
090 * final SomeObject arg = problem.decode(gt);
091 * }</pre>
092 *
093 * @since 4.2
094 *
095 * @see Codec#decode(Genotype)
096 *
097 * @param genotype the genotype to be converted
098 * @return the converted genotype
099 * @throws NullPointerException if the given {@code genotype} is {@code null}
100 */
101 public default T decode(final Genotype<G> genotype) {
102 return codec().decode(genotype);
103 }
104
105 /**
106 * Returns the fitness value for the given argument.
107 *
108 * @since 4.1
109 *
110 * @param arg the argument of the fitness function
111 * @return the fitness value
112 */
113 public default C fitness(final T arg) {
114 return fitness().apply(arg);
115 }
116
117 /**
118 * Returns the fitness value for the given argument.
119 *
120 * @since 4.1
121 *
122 * @param genotype the argument of the fitness function
123 * @return the fitness value
124 */
125 public default C fitness(final Genotype<G> genotype) {
126 return fitness(codec().decode(genotype));
127 }
128
129 /**
130 * Return a new optimization <i>problem</i> with the given parameters.
131 *
132 * @param fitness the problem fitness function
133 * @param codec the evolution engine codec
134 * @param <T> the (<i>native</i>) argument type of the problem fitness function
135 * @param <G> the gene type the evolution engine is working with
136 * @param <C> the result type of the fitness function
137 * @return a new problem object from the given parameters
138 * @throws NullPointerException if one of the arguments is {@code null}
139 */
140 public static <T, G extends Gene<?, G>, C extends Comparable<? super C>>
141 Problem<T, G, C> of(
142 final Function<T, C> fitness,
143 final Codec<T, G> codec
144 ) {
145 requireNonNull(fitness);
146 requireNonNull(codec);
147
148 return new Problem<T, G, C>() {
149 @Override
150 public Codec<T, G> codec() {
151 return codec;
152 }
153
154 @Override
155 public Function<T, C> fitness() {
156 return fitness;
157 }
158 };
159 }
160
161 }
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