OrderedCrossover.java
- /*
- * 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.math4.legacy.genetics;
- import java.util.ArrayList;
- import java.util.Collections;
- import java.util.HashSet;
- import java.util.List;
- import java.util.Set;
- import org.apache.commons.math4.legacy.exception.DimensionMismatchException;
- import org.apache.commons.math4.legacy.exception.MathIllegalArgumentException;
- import org.apache.commons.math4.legacy.exception.util.LocalizedFormats;
- import org.apache.commons.rng.UniformRandomProvider;
- import org.apache.commons.math4.core.jdkmath.JdkMath;
- /**
- * Order 1 Crossover [OX1] builds offspring from <b>ordered</b> chromosomes by copying a
- * consecutive slice from one parent, and filling up the remaining genes from the other
- * parent as they appear.
- * <p>
- * This policy works by applying the following rules:
- * <ol>
- * <li>select a random slice of consecutive genes from parent 1</li>
- * <li>copy the slice to child 1 and mark out the genes in parent 2</li>
- * <li>starting from the right side of the slice, copy genes from parent 2 as they
- * appear to child 1 if they are not yet marked out.</li>
- * </ol>
- * <p>
- * Example (random sublist from index 3 to 7, underlined):
- * <pre>
- * p1 = (8 4 7 3 6 2 5 1 9 0) X c1 = (0 4 7 3 6 2 5 1 8 9)
- * --------- ---------
- * p2 = (0 1 2 3 4 5 6 7 8 9) X c2 = (8 1 2 3 4 5 6 7 9 0)
- * </pre>
- * <p>
- * This policy works only on {@link AbstractListChromosome}, and therefore it
- * is parameterized by T. Moreover, the chromosomes must have same lengths.
- *
- * @see <a href="http://www.rubicite.com/Tutorials/GeneticAlgorithms/CrossoverOperators/Order1CrossoverOperator.aspx">
- * Order 1 Crossover Operator</a>
- *
- * @param <T> generic type of the {@link AbstractListChromosome}s for crossover
- * @since 3.1
- */
- public class OrderedCrossover<T> implements CrossoverPolicy {
- /**
- * {@inheritDoc}
- *
- * @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
- */
- @Override
- @SuppressWarnings("unchecked")
- 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 mate((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
- */
- protected ChromosomePair mate(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> child1 = new ArrayList<>(length);
- final List<T> child2 = new ArrayList<>(length);
- // sets of already inserted items for quick access
- final Set<T> child1Set = new HashSet<>(length);
- final Set<T> child2Set = new HashSet<>(length);
- final UniformRandomProvider random = GeneticAlgorithm.getRandomGenerator();
- // choose random points, making sure that lb < ub.
- int a = random.nextInt(length);
- int b;
- do {
- b = random.nextInt(length);
- } while (a == b);
- // determine the lower and upper bounds
- final int lb = JdkMath.min(a, b);
- final int ub = JdkMath.max(a, b);
- // add the subLists that are between lb and ub
- child1.addAll(parent1Rep.subList(lb, ub + 1));
- child1Set.addAll(child1);
- child2.addAll(parent2Rep.subList(lb, ub + 1));
- child2Set.addAll(child2);
- // iterate over every item in the parents
- for (int i = 1; i <= length; i++) {
- final int idx = (ub + i) % length;
- // retrieve the current item in each parent
- final T item1 = parent1Rep.get(idx);
- final T item2 = parent2Rep.get(idx);
- // if the first child already contains the item in the second parent add it
- if (!child1Set.contains(item2)) {
- child1.add(item2);
- child1Set.add(item2);
- }
- // if the second child already contains the item in the first parent add it
- if (!child2Set.contains(item1)) {
- child2.add(item1);
- child2Set.add(item1);
- }
- }
- // rotate so that the original slice is in the same place as in the parents.
- Collections.rotate(child1, lb);
- Collections.rotate(child2, lb);
- return new ChromosomePair(first.newFixedLengthChromosome(child1),
- second.newFixedLengthChromosome(child2));
- }
- }