001 /*
002 * Java Genetic Algorithm Library (jenetics-6.1.0).
003 * Copyright (c) 2007-2020 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 java.util.function.Function;
023 import java.util.function.Predicate;
024 import java.util.function.Supplier;
025 import java.util.stream.Stream;
026
027 import io.jenetics.Gene;
028 import io.jenetics.internal.engine.EvolutionStreamImpl;
029
030 /**
031 * The {@code EvolutionStream} class extends the Java {@link Stream} and adds a
032 * method for limiting the evolution by a given predicate.
033 *
034 * @implNote Collecting an <em>empty</em> {@code EvolutionStream} will return
035 * {@code null}.
036 * <pre>{@code
037 * final EvolutionResult<DoubleGene, Double> result = engine.stream()
038 * .limit(0)
039 * .collect(toBestEvolutionResult());
040 *
041 * assert result == null;
042 * }</pre>
043 *
044 * @see java.util.stream.Stream
045 * @see Engine
046 * @see EvolutionStreamable
047 *
048 * @author <a href="mailto:franz.wilhelmstoetter@gmail.com">Franz Wilhelmstötter</a>
049 * @since 3.0
050 * @version 6.0
051 */
052 public interface EvolutionStream<
053 G extends Gene<?, G>,
054 C extends Comparable<? super C>
055 >
056 extends Stream<EvolutionResult<G, C>>
057 {
058
059 /**
060 * Returns a stream consisting of the elements of this stream, truncated
061 * when the given {@code proceed} predicate returns {@code false}.
062 * <p>
063 * <i>General usage example:</i>
064 * <pre>{@code
065 * final Phenotype<DoubleGene, Double> result = engine.stream()
066 * // Truncate the evolution stream after 5 "steady" generations.
067 * .limit(bySteadyFitness(5))
068 * // The evolution will stop after maximal 100 generations.
069 * .limit(100)
070 * .collect(toBestPhenotype());
071 * }</pre>
072 *
073 * <b>Note:</b>
074 * The evolution result may be {@code null}, if your <em>truncation</em>
075 * predicate returns {@code false} for the initial population.
076 * <pre>{@code
077 * final EvolutionResult<DoubleGene, Double> result = engine.stream()
078 * .limit(er -> false)
079 * .collect(toBestEvolutionResult());
080 *
081 * assert result == null;
082 * }</pre>
083 *
084 * @see Limits
085 *
086 * @param proceed the predicate which determines whether the stream is
087 * truncated or not. <i>If the predicate returns {@code false}, the
088 * evolution stream is truncated.</i>
089 * @return the new stream
090 * @throws NullPointerException if the given predicate is {@code null}.
091 */
092 EvolutionStream<G, C>
093 limit(final Predicate<? super EvolutionResult<G, C>> proceed);
094
095 /**
096 * Create a new {@code EvolutionStream} from the given {@code start}
097 * population and {@code evolution} function. The main purpose of this
098 * factory method is to simplify the creation of an {@code EvolutionStream}
099 * from an own evolution (GA) engine.
100 *
101 * <pre>{@code
102 * final Supplier<EvolutionStart<DoubleGene, Double>> start = ...
103 * final EvolutionStream<DoubleGene, Double> stream =
104 * EvolutionStream.of(start, new MySpecialEngine());
105 * }</pre>
106 *
107 * A more complete example for would look like as:
108 *
109 * <pre>{@code
110 * public final class SpecialEngine {
111 *
112 * // The fitness function.
113 * private static Double fitness(final Genotype<DoubleGene> gt) {
114 * return gt.gene().allele();
115 * }
116 *
117 * // Create new evolution start object.
118 * private static EvolutionStart<DoubleGene, Double>
119 * start(final int populationSize, final long generation) {
120 * final Population<DoubleGene, Double> population =
121 * Genotype.of(DoubleChromosome.of(0, 1)).instances()
122 * .map(gt -> Phenotype.of(gt, generation, SpecialEngine::fitness))
123 * .limit(populationSize)
124 * .collect(Population.toPopulation());
125 *
126 * return EvolutionStart.of(population, generation);
127 * }
128 *
129 * // The special evolution function.
130 * private static EvolutionResult<DoubleGene, Double>
131 * evolve(final EvolutionStart<DoubleGene, Double> start) {
132 * // Your special evolution implementation comes here!
133 * return null;
134 * }
135 *
136 * public static void main(final String[] args) {
137 * final Genotype<DoubleGene> best = EvolutionStream
138 * .ofEvolution(() -> start(50, 0), SpecialEngine::evolve)
139 * .limit(Limits.bySteadyFitness(10))
140 * .limit(1000)
141 * .collect(EvolutionResult.toBestGenotype());
142 *
143 * System.out.println(String.format("Best Genotype: %s", best));
144 * }
145 * }
146 * }</pre>
147 *
148 *
149 * @since 5.1
150 *
151 * @see #ofAdjustableEvolution(Supplier, Function)
152 *
153 * @param <G> the gene type
154 * @param <C> the fitness type
155 * @param start the evolution start
156 * @param evolution the evolution function
157 * @return a new {@code EvolutionStream} with the given {@code start} and
158 * {@code evolution} function
159 * @throws java.lang.NullPointerException if one of the arguments is
160 * {@code null}
161 */
162 static <G extends Gene<?, G>, C extends Comparable<? super C>>
163 EvolutionStream<G, C> ofEvolution(
164 final Supplier<EvolutionStart<G, C>> start,
165 final Evolution<G, C> evolution
166 ) {
167 return new EvolutionStreamImpl<>(start, evolution);
168 }
169
170 /**
171 * Create a new evolution stream with an <em>adjustable</em> evolution
172 * function.
173 *
174 * <pre>{@code
175 * public static void main(final String[] args) {
176 * final Problem<double[], DoubleGene, Double> problem = Problem.of(
177 * v -> Math.sin(v[0])*Math.cos(v[1]),
178 * Codecs.ofVector(DoubleRange.of(0, 2*Math.PI), 2)
179 * );
180 *
181 * // Engine builder template.
182 * final Engine.Builder<DoubleGene, Double> builder = Engine
183 * .builder(problem)
184 * .minimizing();
185 *
186 * // Evolution used for low fitness variance.
187 * final Evolution<DoubleGene, Double> lowVar = builder.copy()
188 * .alterers(new Mutator<>(0.5))
189 * .selector(new MonteCarloSelector<>())
190 * .build();
191 *
192 * // Evolution used for high fitness variance.
193 * final Evolution<DoubleGene, Double> highVar = builder.copy()
194 * .alterers(
195 * new Mutator<>(0.05),
196 * new MeanAlterer<>())
197 * .selector(new RouletteWheelSelector<>())
198 * .build();
199 *
200 * final EvolutionStream<DoubleGene, Double> stream =
201 * EvolutionStream.ofAdjustableEvolution(
202 * EvolutionStart::empty,
203 * er -> var(er) < 0.2 ? lowVar : highVar
204 * );
205 *
206 * final Genotype<DoubleGene> result = stream
207 * .limit(Limits.bySteadyFitness(50))
208 * .collect(EvolutionResult.toBestGenotype());
209 *
210 * System.out.println(result + ": " +
211 * problem.fitness().apply(problem.codec().decode(result)));
212 * }
213 *
214 * private static double var(final EvolutionStart<DoubleGene, Double> result) {
215 * return result != null
216 * ? result.getPopulation().stream()
217 * .map(Phenotype::fitness)
218 * .collect(DoubleMoments.toDoubleMoments())
219 * .variance()
220 * : 0.0;
221 * }
222 * }</pre>
223 *
224 * @see #ofEvolution(Supplier, Evolution)
225 *
226 * @param start the evolution start object
227 * @param evolution the adaptable evolution function
228 * @param <G> the gene type
229 * @param <C> the fitness type
230 * @return a new {@code EvolutionStream} with the given {@code start} and
231 * {@code evolution} function
232 * @throws java.lang.NullPointerException if one of the arguments is
233 * {@code null}
234 */
235 static <G extends Gene<?, G>, C extends Comparable<? super C>>
236 EvolutionStream<G, C> ofAdjustableEvolution(
237 final Supplier<EvolutionStart<G, C>> start,
238 final Function<
239 ? super EvolutionStart<G, C>,
240 ? extends Evolution<G, C>> evolution
241 ) {
242 return EvolutionStreamImpl.of(start, evolution);
243 }
244
245 }
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