01 /*
02 * Java Genetic Algorithm Library (jenetics-4.3.0).
03 * Copyright (c) 2007-2018 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;
21
22 import static java.lang.String.format;
23 import static io.jenetics.internal.math.random.indexes;
24
25 import java.util.Random;
26
27 import io.jenetics.util.MSeq;
28
29 /**
30 * The {@code SwapMutation} changes the order of genes in a chromosome, with the
31 * hope of bringing related genes closer together, thereby facilitating the
32 * production of building blocks. This mutation operator can also be used for
33 * combinatorial problems, where no duplicated genes within a chromosome are
34 * allowed, e.g. for the TSP.
35 *
36 * @author <a href="mailto:franz.wilhelmstoetter@gmail.com">Franz Wilhelmstötter</a>
37 * @since 1.0
38 * @version 4.0
39 */
40 public class SwapMutator<
41 G extends Gene<?, G>,
42 C extends Comparable<? super C>
43 >
44 extends Mutator<G, C>
45 {
46
47 /**
48 * Constructs an alterer with a given recombination probability.
49 *
50 * @param probability the crossover probability.
51 * @throws IllegalArgumentException if the {@code probability} is not in the
52 * valid range of {@code [0, 1]}.
53 */
54 public SwapMutator(final double probability) {
55 super(probability);
56 }
57
58 /**
59 * Default constructor, with default mutation probability
60 * ({@link AbstractAlterer#DEFAULT_ALTER_PROBABILITY}).
61 */
62 public SwapMutator() {
63 this(DEFAULT_ALTER_PROBABILITY);
64 }
65
66 /**
67 * Swaps the genes in the given array, with the mutation probability of this
68 * mutation.
69 */
70 @Override
71 protected MutatorResult<Chromosome<G>> mutate(
72 final Chromosome<G> chromosome,
73 final double p,
74 final Random random
75 ) {
76 final MutatorResult<Chromosome<G>> result;
77 if (chromosome.length() > 1) {
78 final MSeq<G> genes = chromosome.toSeq().copy();
79 final int mutations = (int)indexes(random, genes.length(), p)
80 .peek(i -> genes.swap(i, random.nextInt(genes.length())))
81 .count();
82 result = MutatorResult.of(
83 chromosome.newInstance(genes.toISeq()),
84 mutations
85 );
86 } else {
87 result = MutatorResult.of(chromosome);
88 }
89
90 return result;
91 }
92
93 @Override
94 public String toString() {
95 return format("%s[p=%f]", getClass().getSimpleName(), _probability);
96 }
97
98 }
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