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Diffstat (limited to 'src/main/java/org/apache/commons/math3/genetics/OnePointCrossover.java')
| -rw-r--r-- | src/main/java/org/apache/commons/math3/genetics/OnePointCrossover.java | 128 |
1 files changed, 128 insertions, 0 deletions
diff --git a/src/main/java/org/apache/commons/math3/genetics/OnePointCrossover.java b/src/main/java/org/apache/commons/math3/genetics/OnePointCrossover.java new file mode 100644 index 0000000..9514771 --- /dev/null +++ b/src/main/java/org/apache/commons/math3/genetics/OnePointCrossover.java @@ -0,0 +1,128 @@ +/* + * Licensed to the Apache Software Foundation (ASF) under one or more + * contributor license agreements. See the NOTICE file distributed with + * this work for additional information regarding copyright ownership. + * The ASF licenses this file to You under the Apache License, Version 2.0 + * (the "License"); you may not use this file except in compliance with + * the License. You may obtain a copy of the License at + * + * http://www.apache.org/licenses/LICENSE-2.0 + * + * Unless required by applicable law or agreed to in writing, software + * distributed under the License is distributed on an "AS IS" BASIS, + * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. + * See the License for the specific language governing permissions and + * limitations under the License. + */ +package org.apache.commons.math3.genetics; + +import org.apache.commons.math3.exception.DimensionMismatchException; +import org.apache.commons.math3.exception.MathIllegalArgumentException; +import org.apache.commons.math3.exception.util.LocalizedFormats; + +import java.util.ArrayList; +import java.util.List; + +/** + * One point crossover policy. A random crossover point is selected and the first part from each + * parent is copied to the corresponding child, and the second parts are copied crosswise. + * + * <p>Example: + * + * <pre> + * -C- denotes a crossover point + * -C- -C- + * p1 = (1 0 1 0 0 1 | 0 1 1) X p2 = (0 1 1 0 1 0 | 1 1 1) + * \------------/ \-----/ \------------/ \-----/ + * || (*) || (**) + * VV (**) VV (*) + * /------------\ /-----\ /------------\ /-----\ + * c1 = (1 0 1 0 0 1 | 1 1 1) X c2 = (0 1 1 0 1 0 | 0 1 1) + * </pre> + * + * This policy works only on {@link AbstractListChromosome}, and therefore it is parameterized by T. + * Moreover, the chromosomes must have same lengths. + * + * @param <T> generic type of the {@link AbstractListChromosome}s for crossover + * @since 2.0 + */ +public class OnePointCrossover<T> implements CrossoverPolicy { + + /** + * Performs one point crossover. A random crossover point is selected and the first part from + * each parent is copied to the corresponding child, and the second parts are copied crosswise. + * + * <p>Example: + * + * <pre> + * -C- denotes a crossover point + * -C- -C- + * p1 = (1 0 1 0 0 1 | 0 1 1) X p2 = (0 1 1 0 1 0 | 1 1 1) + * \------------/ \-----/ \------------/ \-----/ + * || (*) || (**) + * VV (**) VV (*) + * /------------\ /-----\ /------------\ /-----\ + * c1 = (1 0 1 0 0 1 | 1 1 1) X c2 = (0 1 1 0 1 0 | 0 1 1) + * </pre> + * + * @param first first parent (p1) + * @param second second parent (p2) + * @return pair of two children (c1,c2) + * @throws MathIllegalArgumentException iff one of the chromosomes is not an instance of {@link + * AbstractListChromosome} + * @throws DimensionMismatchException if the length of the two chromosomes is different + */ + @SuppressWarnings("unchecked") // OK because of instanceof checks + public ChromosomePair crossover(final Chromosome first, final Chromosome second) + throws DimensionMismatchException, MathIllegalArgumentException { + + if (!(first instanceof AbstractListChromosome<?> + && second instanceof AbstractListChromosome<?>)) { + throw new MathIllegalArgumentException( + LocalizedFormats.INVALID_FIXED_LENGTH_CHROMOSOME); + } + return crossover((AbstractListChromosome<T>) first, (AbstractListChromosome<T>) second); + } + + /** + * Helper for {@link #crossover(Chromosome, Chromosome)}. Performs the actual crossover. + * + * @param first the first chromosome. + * @param second the second chromosome. + * @return the pair of new chromosomes that resulted from the crossover. + * @throws DimensionMismatchException if the length of the two chromosomes is different + */ + private ChromosomePair crossover( + final AbstractListChromosome<T> first, final AbstractListChromosome<T> second) + throws DimensionMismatchException { + final int length = first.getLength(); + if (length != second.getLength()) { + throw new DimensionMismatchException(second.getLength(), length); + } + + // array representations of the parents + final List<T> parent1Rep = first.getRepresentation(); + final List<T> parent2Rep = second.getRepresentation(); + // and of the children + final List<T> child1Rep = new ArrayList<T>(length); + final List<T> child2Rep = new ArrayList<T>(length); + + // select a crossover point at random (0 and length makes no sense) + final int crossoverIndex = 1 + (GeneticAlgorithm.getRandomGenerator().nextInt(length - 2)); + + // copy the first part + for (int i = 0; i < crossoverIndex; i++) { + child1Rep.add(parent1Rep.get(i)); + child2Rep.add(parent2Rep.get(i)); + } + // and switch the second part + for (int i = crossoverIndex; i < length; i++) { + child1Rep.add(parent2Rep.get(i)); + child2Rep.add(parent1Rep.get(i)); + } + + return new ChromosomePair( + first.newFixedLengthChromosome(child1Rep), + second.newFixedLengthChromosome(child2Rep)); + } +} |