001 /*
002 * Java Genetic Algorithm Library (jenetics-7.1.2).
003 * Copyright (c) 2007-2023 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.engine;
021
022 import java.util.ArrayList;
023 import java.util.Collection;
024 import java.util.Collections;
025 import java.util.List;
026 import java.util.Spliterator;
027 import java.util.concurrent.atomic.AtomicReference;
028 import java.util.function.Supplier;
029 import java.util.stream.BaseStream;
030
031 import io.jenetics.Gene;
032 import io.jenetics.engine.EvolutionInit;
033 import io.jenetics.engine.EvolutionResult;
034 import io.jenetics.engine.EvolutionStart;
035 import io.jenetics.engine.EvolutionStream;
036 import io.jenetics.engine.EvolutionStreamable;
037 import io.jenetics.internal.engine.EvolutionStreamImpl;
038
039 import io.jenetics.ext.internal.util.ConcatSpliterator;
040
041 /**
042 * The {@code ConcatEngine} lets you concatenate two (or more) evolution
043 * {@link io.jenetics.engine.Engine}, with different configurations, and let it
044 * use as <em>one</em> engine {@link EvolutionStreamable}.
045 *
046 * <pre> {@code
047 * +----------+ +----------+
048 * | ES | | ES |
049 * +-------+----+ | +-------+----+ |
050 * (Start) | +-----+ Start | +-----+
051 * ------>| Engine 1 |------------>| Engine 2 |----------->
052 * | | Result | | Result
053 * +------------+ +------------+
054 * }</pre>
055 *
056 * The sketch above shows how the engine concatenation works. In this example,
057 * the evolution stream of the first engine is evaluated until it terminates.
058 * The result of the first stream is then used as start input of the second
059 * evolution stream, which then delivers the final result.
060 * <p>
061 * Concatenating evolution engines might be useful, if you want to explore your
062 * search space with random search first and then start the <em>real</em> GA
063 * search.
064 * <pre>{@code
065 * final Problem<double[], DoubleGene, Double> problem = Problem.of(
066 * v -> Math.sin(v[0])*Math.cos(v[1]),
067 * Codecs.ofVector(DoubleRange.of(0, 2*Math.PI), 2)
068 * );
069 *
070 * final Engine<DoubleGene, Double> engine1 = Engine.builder(problem)
071 * .minimizing()
072 * .alterers(new Mutator<>(0.2))
073 * .selector(new MonteCarloSelector<>())
074 * .build();
075 *
076 * final Engine<DoubleGene, Double> engine2 = Engine.builder(problem)
077 * .minimizing()
078 * .alterers(
079 * new Mutator<>(0.1),
080 * new MeanAlterer<>())
081 * .selector(new RouletteWheelSelector<>())
082 * .build();
083 *
084 * final Genotype<DoubleGene> result =
085 * ConcatEngine.of(
086 * engine1.limit(50),
087 * engine2.limit(() -> Limits.bySteadyFitness(30)))
088 * .stream()
089 * .collect(EvolutionResult.toBestGenotype());
090 *
091 * System.out.println(result + ": " +
092 * problem.fitness().apply(problem.codec().decode(result)));
093 * }</pre>
094 *
095 * An essential part, when concatenating evolution engines, is to make sure your
096 * your engines are creating <em>limited</em> evolution streams. This is what
097 * the {@link EvolutionStreamable#limit(Supplier)} and
098 * {@link EvolutionStreamable#limit(long)} methods are for. Limiting an engine
099 * means, that this engine will surely create only streams, which are limited
100 * with the predicate/generation given to the engine. If you have limited your
101 * engines, it is no longer necessary to limit your final evolution stream, but
102 * your are still able to do so.
103 *
104 * @see CyclicEngine
105 *
106 * @param <G> the gene type
107 * @param <C> the fitness type
108 *
109 * @author <a href="mailto:franz.wilhelmstoetter@gmail.com">Franz Wilhelmstötter</a>
110 * @version 4.1
111 * @since 4.1
112 */
113 public final class ConcatEngine<
114 G extends Gene<?, G>,
115 C extends Comparable<? super C>
116 >
117 extends EnginePool<G, C>
118 {
119
120 /**
121 * Create a new concatenating evolution engine with the given list of engines.
122 *
123 * @param engines the engines which are concatenated to <em>one</em> engine
124 * @throws NullPointerException if the {@code engines} or one of it's
125 * elements is {@code null}
126 */
127 public ConcatEngine(final List<? extends EvolutionStreamable<G, C>> engines) {
128 super(engines);
129 }
130
131 @Override
132 public EvolutionStream<G, C>
133 stream(final Supplier<EvolutionStart<G, C>> start) {
134 final AtomicReference<EvolutionStart<G, C>> other =
135 new AtomicReference<>(null);
136
137 return new EvolutionStreamImpl<>(
138 new ConcatSpliterator<>(
139 _engines.stream()
140 .map(engine -> engine
141 .stream(() -> start(start, other))
142 .peek(result -> other.set(result.toEvolutionStart())))
143 .map(BaseStream::spliterator)
144 .toList()
145 ),
146 false
147 );
148 }
149
150 private EvolutionStart<G, C> start(
151 final Supplier<EvolutionStart<G, C>> first,
152 final AtomicReference<EvolutionStart<G, C>> other
153 ) {
154 return other.get() != null ? other.get() : first.get();
155 }
156
157 @Override
158 public EvolutionStream<G, C> stream(final EvolutionInit<G> init) {
159 final AtomicReference<EvolutionStart<G, C>> other =
160 new AtomicReference<>(null);
161
162 return new EvolutionStreamImpl<>(
163 new ConcatSpliterator<>(spliterators(init, other)),
164 false
165 );
166 }
167
168 private Collection<Spliterator<EvolutionResult<G, C>>> spliterators(
169 final EvolutionInit<G> init,
170 final AtomicReference<EvolutionStart<G, C>> other
171 ) {
172 final Collection<Spliterator<EvolutionResult<G, C>>> result;
173 if (_engines.isEmpty()) {
174 result = Collections.emptyList();
175 } else if (_engines.size() == 1) {
176 result = List.of(
177 _engines.get(0)
178 .stream(init)
179 .peek(er -> other.set(er.toEvolutionStart()))
180 .spliterator()
181 );
182 } else {
183 final List<Spliterator<EvolutionResult<G, C>>> concat =
184 new ArrayList<>();
185
186 concat.add(
187 _engines.get(0)
188 .stream(init)
189 .peek(er -> other.set(er.toEvolutionStart()))
190 .spliterator()
191 );
192 concat.addAll(
193 _engines.subList(1, _engines.size()).stream()
194 .map(engine -> engine
195 .stream(other::get)
196 .peek(er -> other.set(er.toEvolutionStart())))
197 .map(BaseStream::spliterator)
198 .toList()
199 );
200
201 result = concat;
202 }
203
204 return result;
205 }
206
207 /**
208 * Create a new concatenating evolution engine with the given array of
209 * engines.
210 *
211 * @param engines the engines which are concatenated to <em>one</em> engine
212 * @param <G> the gene type
213 * @param <C> the fitness type
214 * @return a new concatenating evolution engine
215 * @throws NullPointerException if the {@code engines} or one of it's
216 * elements is {@code null}
217 */
218 @SafeVarargs
219 public static <G extends Gene<?, G>, C extends Comparable<? super C>>
220 ConcatEngine<G, C> of(final EvolutionStreamable<G, C>... engines) {
221 return new ConcatEngine<>(List.of(engines));
222 }
223
224
225 }
|