01 /*
02 * Java Genetic Algorithm Library (jenetics-7.1.2).
03 * Copyright (c) 2007-2023 Franz Wilhelmstötter
04 *
05 * Licensed under the Apache License, Version 2.0 (the "License");
06 * you may not use this file except in compliance with the License.
07 * You may obtain a copy of the License at
08 *
09 * http://www.apache.org/licenses/LICENSE-2.0
10 *
11 * Unless required by applicable law or agreed to in writing, software
12 * distributed under the License is distributed on an "AS IS" BASIS,
13 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
14 * See the License for the specific language governing permissions and
15 * limitations under the License.
16 *
17 * Author:
18 * Franz Wilhelmstötter (franz.wilhelmstoetter@gmail.com)
19 */
20 package io.jenetics.ext.engine;
21
22 import static java.util.Objects.requireNonNull;
23
24 import java.util.function.Function;
25
26 import io.jenetics.Alterer;
27 import io.jenetics.Gene;
28 import io.jenetics.engine.Engine;
29 import io.jenetics.engine.EvolutionResult;
30 import io.jenetics.engine.EvolutionStreamable;
31 import io.jenetics.stat.DoubleMomentStatistics;
32 import io.jenetics.util.DoubleRange;
33
34 /**
35 * @author <a href="mailto:franz.wilhelmstoetter@gmail.com">Franz Wilhelmstötter</a>
36 * @version 5.0
37 * @since 5.0
38 */
39 final class FitnessVarianceAdaptiveEngine<
40 G extends Gene<?, G>,
41 N extends Number & Comparable<? super N>
42 >
43 implements Function<EvolutionResult<G, N>, EvolutionStreamable<G, N>>
44 {
45
46 private final DoubleRange _variance;
47 private final Engine.Builder<G, N> _builder;
48 private final Alterer<G, N> _narrow;
49 private final Alterer<G, N> _enlarge;
50
51 private Engine<G, N> _engine;
52 private boolean _narrowing;
53
54 FitnessVarianceAdaptiveEngine(
55 final DoubleRange variance,
56 final Engine.Builder<G, N> builder,
57 final Alterer<G, N> narrow,
58 final Alterer<G, N> enlarge
59 ) {
60 _variance = requireNonNull(variance);
61 _builder = requireNonNull(builder).copy();
62 _narrow = requireNonNull(narrow);
63 _enlarge = requireNonNull(enlarge);
64 }
65
66 @Override
67 public EvolutionStreamable<G, N> apply(final EvolutionResult<G, N> result) {
68 if (result == null || _engine == null) {
69 _engine = _builder
70 .alterers(_enlarge)
71 .build();
72 _narrowing = false;
73 } else {
74 final DoubleMomentStatistics stat = new DoubleMomentStatistics();
75
76 result.population()
77 .forEach(pt -> stat.accept(pt.fitness().doubleValue()));
78
79 if (stat.variance() < _variance.min() && _narrowing) {
80 _engine = _builder
81 .alterers(_enlarge)
82 .build();
83 _narrowing = false;
84 } else if (stat.variance() > _variance.max() && !_narrowing) {
85 _engine = _builder
86 .alterers(_narrow)
87 .build();
88 _narrowing = true;
89 }
90 }
91
92 assert _engine != null;
93 return _engine;
94 }
95
96 }
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