001 /*
002 * Java Genetic Algorithm Library (jenetics-4.1.0).
003 * Copyright (c) 2007-2018 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;
021
022 import static java.lang.Math.min;
023 import static java.lang.String.format;
024 import static io.jenetics.internal.math.random.nextDouble;
025
026 import java.util.Random;
027
028 import io.jenetics.internal.util.Hash;
029 import io.jenetics.internal.util.require;
030 import io.jenetics.util.MSeq;
031 import io.jenetics.util.RandomRegistry;
032
033 /**
034 * This alterer takes two chromosome (treating it as vectors) and creates a
035 * linear combination of this vectors as result. The line-recombination depends
036 * on a variable <em>p</em> which determines how far out along the line (defined
037 * by the two multidimensional points/vectors) the children are allowed to be.
038 * If <em>p</em> = 0 then the children will be located along the line within the
039 * hypercube between the two points. If <em>p</em> > 0 then the children may
040 * be located anywhere on the line, even somewhat outside of the hypercube.
041 * <p>
042 * Points outside of the allowed numeric range are rejected and the original
043 * value are used instead. The strategy on how out-of-range points are handled,
044 * is the difference to the very similar {@link IntermediateCrossover}.
045 *
046 * @see <a href="https://cs.gmu.edu/~sean/book/metaheuristics/"><em>
047 * Essentials of Metaheuristic, page 42</em></a>
048 * @see IntermediateCrossover
049 *
050 * @author <a href="mailto:franz.wilhelmstoetter@gmail.com">Franz Wilhelmstötter</a>
051 * @version 3.8
052 * @since 3.8
053 */
054 public class LineCrossover<
055 G extends NumericGene<?, G>,
056 C extends Comparable<? super C>
057 >
058 extends Crossover<G, C>
059 {
060
061 private final double _p;
062
063 /**
064 * Creates a new linear-crossover with the given recombination
065 * probability and the line-scaling factor <em>p</em>.
066 *
067 * @param probability the recombination probability.
068 * @param p defines the possible location of the recombined chromosomes. If
069 * <em>p</em> = 0 then the children will be located along the line
070 * within the hypercube between the two points. If <em>p</em> > 0
071 * then the children may be located anywhere on the line, even
072 * somewhat outside of the hypercube.
073 * @throws IllegalArgumentException if the {@code probability} is not in the
074 * valid range of {@code [0, 1]} or if {@code p} is smaller then zero
075 */
076 public LineCrossover(final double probability, final double p) {
077 super(probability);
078 _p = require.nonNegative(p, "p");
079 }
080
081 /**
082 * Creates a new linear-crossover with the given recombination
083 * probability. The parameter <em>p</em> is set to zero, which restricts the
084 * recombined chromosomes within the hypercube of the selected chromosomes
085 * (vectors).
086 *
087 * @param probability the recombination probability.
088 * @throws IllegalArgumentException if the {@code probability} is not in the
089 * valid range of {@code [0, 1]}
090 */
091 public LineCrossover(final double probability) {
092 this(probability, 0);
093 }
094
095 /**
096 * Creates a new linear-crossover with default recombination
097 * probability ({@link #DEFAULT_ALTER_PROBABILITY}) and a <em>p</em> value
098 * of zero, which restricts the recombined chromosomes within the hypercube
099 * of the selected chromosomes (vectors).
100 */
101 public LineCrossover() {
102 this(DEFAULT_ALTER_PROBABILITY, 0);
103 }
104
105 @Override
106 protected int crossover(final MSeq<G> v, final MSeq<G> w) {
107 final Random random = RandomRegistry.getRandom();
108
109 final double min = v.get(0).getMin().doubleValue();
110 final double max = v.get(0).getMax().doubleValue();
111
112 final double a = nextDouble(-_p, 1 + _p, random);
113 final double b = nextDouble(-_p, 1 + _p, random);
114
115 boolean changed = false;
116 for (int i = 0, n = min(v.length(), w.length()); i < n; ++i) {
117 final double vi = v.get(i).doubleValue();
118 final double wi = w.get(i).doubleValue();
119
120 final double t = a*vi + (1 - a)*wi;
121 final double s = b*wi + (1 - b)*vi;
122
123 if (t >= min && s >= min && t < max && s < max) {
124 v.set(i, v.get(i).newInstance(t));
125 w.set(i, w.get(i).newInstance(s));
126 changed = true;
127 }
128 }
129
130 return changed ? 2 : 0;
131 }
132
133 @Override
134 public int hashCode() {
135 return Hash.of(getClass()).and(super.hashCode()).value();
136 }
137
138 @Override
139 public boolean equals(final Object obj) {
140 return obj == this ||
141 obj instanceof LineCrossover &&
142 super.equals(obj);
143 }
144
145 @Override
146 public String toString() {
147 return format("%s[p=%f]", getClass().getSimpleName(), _probability);
148 }
149
150 }
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