001 /*
002 * Java Genetic Algorithm Library (jenetics-3.7.0).
003 * Copyright (c) 2007-2016 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@gmx.at)
019 */
020 package org.jenetics.engine;
021
022 import static java.util.Objects.requireNonNull;
023
024 import java.util.function.BiFunction;
025 import java.util.function.Function;
026
027 import org.jenetics.Gene;
028 import org.jenetics.Genotype;
029 import org.jenetics.util.Factory;
030 import org.jenetics.util.ISeq;
031
032 /**
033 * A problem {@code Codec} contains the information about how to encode a given
034 * argument type into a {@code Genotype}. It also lets convert the encoded
035 * {@code Genotype} back to the argument type. The engine creation and the
036 * implementation of the fitness function can be heavily simplified by using
037 * a {@code Codec} class. The example given in the {@link Engine} documentation
038 * can be simplified as follows:
039 *
040 * <pre>{@code
041 * public class RealFunction {
042 * // The conversion from the 'Genotype' to the argument type of the fitness
043 * // function is performed by the given 'Codec'. You can concentrate on the
044 * // implementation, because you are not bothered with the conversion code.
045 * private static double eval(final double x) {
046 * return cos(0.5 + sin(x)) * cos(x);
047 * }
048 *
049 * public static void main(final String[] args) {
050 * final Engine<DoubleGene, Double> engine = Engine
051 * // Create an Engine.Builder with the "pure" fitness function
052 * // and the appropriate Codec.
053 * .build(RealFunction::eval, codecs.ofScalar(DoubleRange.of(0, 2*PI)))
054 * .build();
055 * ...
056 * }
057 * }
058 * }</pre>
059 *
060 * The {@code Codec} needed for the above usage example, will look like this:
061 * <pre>{@code
062 * final DoubleRange domain = DoubleRange.of(0, 2*PI);
063 * final Codec<Double, DoubleGene> codec = Codec.of(
064 * Genotype.of(DoubleChromosome.of(domain)),
065 * gt -> gt.getChromosome().getGene().getAllele()
066 * );
067 * }</pre>
068 *
069 * Calling the {@link Codec#of(Factory, Function)} method is the usual way for
070 * creating new {@code Codec} instances.
071 *
072 * @see codecs
073 * @see Engine
074 * @see Engine.Builder
075 *
076 * @param <T> the argument type of a given problem
077 * @param <G> the {@code Gene} type used for encoding the argument type {@code T}
078 *
079 * @author <a href="mailto:franz.wilhelmstoetter@gmx.at">Franz Wilhelmstötter</a>
080 * @version 3.6
081 * @since 3.2
082 */
083 public interface Codec<T, G extends Gene<?, G>> {
084
085 /**
086 * Return the genotype factory for creating genotypes with the right
087 * encoding for the given problem. The genotype created with this factory
088 * must work together with the {@link #decoder()} function, which transforms
089 * the genotype into an object of the problem domain.
090 *
091 * <pre>{@code
092 * final Codec<SomeObject, DoubleGene> codec = ...
093 * final Genotype<DoubleGene> gt = codec.encoding().newInstance();
094 * final SomeObject arg = codec.decoder().apply(gt);
095 * }</pre>
096 *
097 * @see #decoder()
098 *
099 * @return the genotype (factory) representation of the problem domain
100 */
101 public Factory<Genotype<G>> encoding();
102
103 /**
104 * Return the <em>decoder</em> function which transforms the genotype back
105 * to the original problem domain representation.
106 *
107 * @see #encoding()
108 *
109 * @return genotype decoder
110 */
111 public Function<Genotype<G>, T> decoder();
112
113 /**
114 * Converts the given {@link Genotype} to the target type {@link T}. This is
115 * a shortcut for
116 * <pre>{@code
117 * final Codec<SomeObject, DoubleGene> codec = ...
118 * final Genotype<DoubleGene> gt = codec.encoding().newInstance();
119 *
120 * final SomeObject arg = codec.decoder().apply(gt);
121 * }</pre>
122 *
123 * @since 3.6
124 *
125 * @param gt the genotype to be converted
126 * @return the converted genotype
127 */
128 public default T decode(final Genotype<G> gt) {
129 return decoder().apply(gt);
130 }
131
132
133 /**
134 * Create a new {@code Codec} object with the given {@code encoding} and
135 * {@code decoder} function.
136 *
137 * @param encoding the genotype factory used for creating new
138 * {@code Genotypes}.
139 * @param decoder decoder function, which converts a {@code Genotype} to a
140 * value in the problem domain.
141 * @param <G> the {@code Gene} type
142 * @param <T> the fitness function argument type in the problem domain
143 * @return a new {@code Codec} object with the given parameters.
144 * @throws NullPointerException if one of the arguments is {@code null}.
145 */
146 public static <G extends Gene<?, G>, T> Codec<T, G> of(
147 final Factory<Genotype<G>> encoding,
148 final Function<Genotype<G>, T> decoder
149 ) {
150 requireNonNull(encoding);
151 requireNonNull(decoder);
152
153 return new Codec<T, G>() {
154 @Override
155 public Factory<Genotype<G>> encoding() {
156 return encoding;
157 }
158
159 @Override
160 public Function<Genotype<G>, T> decoder() {
161 return decoder;
162 }
163 };
164 }
165
166
167 /**
168 * Converts two given {@code Codec} instances into one. This lets you divide
169 * a problem into sub problems and combine them again.
170 * <p>
171 * The following example shows how to combine two codecs, which converts a
172 * {@code LongGene} to a {@code LocalDate}, to a codec which combines the
173 * two {@code LocalDate} object (this are the argument types of the
174 * component codecs) to a {@code Duration}.
175 *
176 * <pre>{@code
177 * final Codec<LocalDate, LongGene> dateCodec1 = Codec.of(
178 * Genotype.of(LongChromosome.of(0, 10_000)),
179 * gt -> LocalDate.ofEpochDay(gt.getGene().longValue())
180 * );
181 *
182 * final Codec<LocalDate, LongGene> dateCodec2 = Codec.of(
183 * Genotype.of(LongChromosome.of(1_000_000, 10_000_000)),
184 * gt -> LocalDate.ofEpochDay(gt.getGene().longValue())
185 * );
186 *
187 * final Codec<Duration, LongGene> durationCodec = Codec.of(
188 * dateCodec1,
189 * dateCodec2,
190 * (d1, d2) -> Duration.ofDays(d2.toEpochDay() - d1.toEpochDay())
191 * );
192 *
193 * final Engine<LongGene, Long> engine = Engine
194 * .builder(Duration::toMillis, durationCodec)
195 * .build();
196 *
197 * final Phenotype<LongGene, Long> pt = engine.stream()
198 * .limit(100)
199 * .collect(EvolutionResult.toBestPhenotype());
200 * System.out.println(pt);
201 *
202 * final Duration duration = durationCodec.decoder()
203 * .apply(pt.getGenotype());
204 * System.out.println(duration);
205 * }</pre>
206 *
207 * @since 3.3
208 *
209 * @param <G> the gene type
210 * @param <A> the argument type of the first codec
211 * @param <B> the argument type of the second codec
212 * @param <T> the argument type of the compound codec
213 * @param codec1 the first codec
214 * @param codec2 the second codec
215 * @param decoder the decoder which combines the two argument types from the
216 * given given codecs, to the argument type of the resulting codec.
217 * @return a new codec which combines the given {@code codec1} and
218 * {@code codec2}
219 * @throws NullPointerException if one of the arguments is {@code null}
220 */
221 public static <G extends Gene<?, G>, A, B, T> Codec<T, G> of(
222 final Codec<A, G> codec1,
223 final Codec<B, G> codec2,
224 final BiFunction<A, B, T> decoder
225 ) {
226 @SuppressWarnings("unchecked")
227 final Function<Object[], T> decoderAdapter =
228 v -> decoder.apply((A)v[0], (B)v[1]);
229
230 return of(
231 ISeq.of(codec1, codec2),
232 decoderAdapter
233 );
234 }
235
236 /**
237 * Combines the given {@code codecs} into one codec. This lets you divide
238 * a problem into sub problems and combine them again.
239 * <p>
240 * The following example combines more than two sub-codecs into one.
241 * <pre>{@code
242 * final Codec<LocalDate, LongGene> dateCodec = Codec.of(
243 * Genotype.of(LongChromosome.of(0, 10_000)),
244 * gt -> LocalDate.ofEpochDay(gt.getGene().longValue())
245 * );
246 *
247 * final Codec<Duration, LongGene> durationCodec = Codec.of(
248 * ISeq.of(dateCodec, dateCodec, dateCodec),
249 * dates -> {
250 * final LocalDate ld1 = (LocalDate)dates[0];
251 * final LocalDate ld2 = (LocalDate)dates[1];
252 * final LocalDate ld3 = (LocalDate)dates[2];
253 *
254 * return Duration.ofDays(
255 * ld1.toEpochDay() + ld2.toEpochDay() - ld3.toEpochDay()
256 * );
257 * }
258 * );
259 *
260 * final Engine<LongGene, Long> engine = Engine
261 * .builder(Duration::toMillis, durationCodec)
262 * .build();
263 *
264 * final Phenotype<LongGene, Long> pt = engine.stream()
265 * .limit(100)
266 * .collect(EvolutionResult.toBestPhenotype());
267 * System.out.println(pt);
268 *
269 * final Duration duration = durationCodec.decoder()
270 * .apply(pt.getGenotype());
271 * System.out.println(duration);
272 * }</pre>
273 *
274 * @since 3.3
275 *
276 * @param <G> the gene type
277 * @param <T> the argument type of the compound codec
278 * @param codecs the {@code Codec} sequence of the sub-problems
279 * @param decoder the decoder which combines the argument types from the
280 * given given codecs, to the argument type of the resulting codec.
281 * @return a new codec which combines the given {@code codecs}
282 * @throws NullPointerException if one of the arguments is {@code null}
283 */
284 public static <G extends Gene<?, G>, T> Codec<T, G> of(
285 final ISeq<? extends Codec<?, G>> codecs,
286 final Function<? super Object[], ? extends T> decoder
287 ) {
288 return new CompositeCodec<>(codecs, decoder);
289 }
290
291 }
|