001/*
002 * Java Genetic Algorithm Library (jenetics-7.2.0).
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 */
020package io.jenetics;
021
022import static java.lang.Math.min;
023import static java.lang.String.format;
024
025import io.jenetics.internal.util.Requires;
026import io.jenetics.util.MSeq;
027import io.jenetics.util.RandomRegistry;
028
029/**
030 * This alterer takes two chromosomes (treating it as vectors) and creates a
031 * linear combination of these vectors as a result. The line-recombination depends
032 * on a variable <em>p</em> which determines how far out along the line (defined
033 * by the two multidimensional points/vectors) the children are allowed to be.
034 * If <em>p</em> = 0 then the children will be located along the line within the
035 * hypercube between the two points. If <em>p</em> &gt; 0 then the children may
036 * be located anywhere on the line, even somewhat outside the hypercube.
037 * <p>
038 * Points outside the allowed numeric range are rejected and the original
039 * value is used instead. The strategy on how out-of-range points are handled,
040 * is the difference to the very similar {@link IntermediateCrossover}.
041 *
042 * @see <a href="https://cs.gmu.edu/~sean/book/metaheuristics/"><em>
043 *       Essentials of Metaheuristic, page 42</em></a>
044 * @see IntermediateCrossover
045 *
046 * @author <a href="mailto:franz.wilhelmstoetter@gmail.com">Franz Wilhelmstötter</a>
047 * @version 3.8
048 * @since 3.8
049 */
050public class LineCrossover<
051        G extends NumericGene<?, G>,
052        C extends Comparable<? super C>
053>
054        extends Crossover<G, C>
055{
056
057        private final double _p;
058
059        /**
060         * Creates a new linear-crossover with the given recombination
061         * probability and the line-scaling factor <em>p</em>.
062         *
063         * @param probability the recombination probability.
064         * @param p defines the possible location of the recombined chromosomes. If
065         *        <em>p</em> = 0 then the children will be located along the line
066         *        within the hypercube between the two points. If <em>p</em> &gt; 0
067         *        then the children may be located anywhere on the line, even
068         *        somewhat outside the hypercube.
069         * @throws IllegalArgumentException if the {@code probability} is not in the
070         *         valid range of {@code [0, 1]} or if {@code p} is smaller then zero
071         */
072        public LineCrossover(final double probability, final double p) {
073                super(probability);
074                _p = Requires.nonNegative(p, "p");
075        }
076
077        /**
078         * Creates a new linear-crossover with the given recombination
079         * probability. The parameter <em>p</em> is set to zero, which restricts the
080         * recombined chromosomes within the hypercube of the selected chromosomes
081         * (vectors).
082         *
083         * @param probability the recombination probability.
084         * @throws IllegalArgumentException if the {@code probability} is not in the
085         *         valid range of {@code [0, 1]}
086         */
087        public LineCrossover(final double probability) {
088                this(probability, 0);
089        }
090
091        /**
092         * Creates a new linear-crossover with default recombination
093         * probability ({@link #DEFAULT_ALTER_PROBABILITY}) and a <em>p</em> value
094         * of zero, which restricts the recombined chromosomes within the hypercube
095         * of the selected chromosomes (vectors).
096         */
097        public LineCrossover() {
098                this(DEFAULT_ALTER_PROBABILITY, 0);
099        }
100
101        @Override
102        protected int crossover(final MSeq<G> v, final MSeq<G> w) {
103                final var random = RandomRegistry.random();
104
105                final double min = v.get(0).min().doubleValue();
106                final double max = v.get(0).max().doubleValue();
107
108                final double a = random.nextDouble(-_p, 1 + _p);
109                final double b = random.nextDouble(-_p, 1 + _p);
110
111                boolean changed = false;
112                for (int i = 0, n = min(v.length(), w.length()); i < n; ++i) {
113                        final double vi = v.get(i).doubleValue();
114                        final double wi = w.get(i).doubleValue();
115
116                        final double t = a*vi + (1 - a)*wi;
117                        final double s = b*wi + (1 - b)*vi;
118
119                        if (t >= min && s >= min && t < max && s < max) {
120                                v.set(i, v.get(i).newInstance(t));
121                                w.set(i, w.get(i).newInstance(s));
122                                changed = true;
123                        }
124                }
125
126                return changed ? 2 : 0;
127        }
128
129        @Override
130        public String toString() {
131                return format("%s[p=%f]", getClass().getSimpleName(), _probability);
132        }
133
134}