[MATH-777] Added OrderedCrossover policy.
git-svn-id: https://svn.apache.org/repos/asf/commons/proper/math/trunk@1369658 13f79535-47bb-0310-9956-ffa450edef68
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Thomas Neidhart
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package org.apache.commons.math3.genetics;
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import java.util.ArrayList;
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import java.util.Collections;
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import java.util.HashSet;
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import java.util.List;
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import java.util.Set;
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import org.apache.commons.math3.exception.DimensionMismatchException;
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import org.apache.commons.math3.exception.MathIllegalArgumentException;
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import org.apache.commons.math3.exception.util.LocalizedFormats;
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import org.apache.commons.math3.random.RandomGenerator;
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import org.apache.commons.math3.util.FastMath;
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/**
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* Order 1 Crossover [OX1] builds offspring from <b>ordered</b> chromosomes by copying a
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* consecutive slice from one parent, and filling up the remaining genes from the other
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* parent as they appear.
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* <p>
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* This policy works by applying the following rules:
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* <ol>
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* <li>select a random slice of consecutive genes from parent 1</li>
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* <li>copy the slice to child 1 and mark out the genes in parent 2</li>
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* <li>starting from the right side of the slice, copy genes from parent 2 as they
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* appear to child 1 if they are not yet marked out.</li>
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* </ol>
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* </p>
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*
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* Example (random sublist from index 3 to 7, underlined):
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* <pre>
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* p1 = (8 4 7 3 6 2 5 1 9 0) X c1 = (0 4 7 3 6 2 5 1 8 9)
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* --------- ---------
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* p2 = (0 1 2 3 4 5 6 7 8 9) X c2 = (8 1 2 3 4 5 6 7 9 0)
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* </pre>
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*
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* This policy works only on {@link AbstractListChromosome}, and therefore it
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* is parameterized by T. Moreover, the chromosomes must have same lengths.
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*
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* @see <a href="http://www.rubicite.com/Tutorials/GeneticAlgorithms/CrossoverOperators/Order1CrossoverOperator.aspx"
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* Order 1 Crossover Operator</a>
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*
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* @param <T> generic type of the {@link AbstractListChromosome}s for crossover
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* @since 3.1
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* @version $Id$
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*/
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public class OrderedCrossover<T> implements CrossoverPolicy {
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/**
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* {@inheritDoc}
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*/
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@SuppressWarnings("unchecked")
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public ChromosomePair crossover(final Chromosome first, final Chromosome second) {
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if (!(first instanceof AbstractListChromosome<?> && second instanceof AbstractListChromosome<?>)) {
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throw new MathIllegalArgumentException(LocalizedFormats.INVALID_FIXED_LENGTH_CHROMOSOME);
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}
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return mate((AbstractListChromosome<T>) first, (AbstractListChromosome<T>) second);
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}
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/**
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* Helper for {@link #crossover(Chromosome, Chromosome)}. Performs the actual crossover.
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*
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* @param first the first chromosome
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* @param second the second chromosome
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* @return the pair of new chromosomes that resulted from the crossover
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* @throws DimensionMismatchException if the length of the two chromosomes is different
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*/
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protected ChromosomePair mate(final AbstractListChromosome<T> first, final AbstractListChromosome<T> second) {
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final int length = first.getLength();
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if (length != second.getLength()) {
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throw new DimensionMismatchException(second.getLength(), length);
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}
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// array representations of the parents
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final List<T> parent1Rep = first.getRepresentation();
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final List<T> parent2Rep = second.getRepresentation();
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// and of the children
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final List<T> child1 = new ArrayList<T>(length);
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final List<T> child2 = new ArrayList<T>(length);
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// sets of already inserted items for quick access
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final Set<T> child1Set = new HashSet<T>(length);
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final Set<T> child2Set = new HashSet<T>(length);
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final RandomGenerator random = GeneticAlgorithm.getRandomGenerator();
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// choose random points, making sure that lb < ub.
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int a = random.nextInt(length);
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int b;
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do {
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b = random.nextInt(length);
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} while (a == b);
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// determine the lower and upper bounds
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final int lb = FastMath.min(a, b);
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final int ub = FastMath.max(a, b);
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// add the subLists that are between lb and ub
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child1.addAll(parent1Rep.subList(lb, ub + 1));
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child1Set.addAll(child1);
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child2.addAll(parent2Rep.subList(lb, ub + 1));
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child2Set.addAll(child2);
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// iterate over every item in the parents
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for (int i = 1; i <= length; i++) {
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final int idx = (ub + i) % length;
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// retrieve the current item in each parent
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final T item1 = parent1Rep.get(idx);
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final T item2 = parent2Rep.get(idx);
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// if the first child already contains the item in the second parent add it
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if (!child1Set.contains(item2)) {
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child1.add(item2);
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child1Set.add(item2);
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}
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// if the second child already contains the item in the first parent add it
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if (!child2Set.contains(item1)) {
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child2.add(item1);
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child2Set.add(item1);
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}
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}
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// rotate so that the original slice is in the same place as in the parents.
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Collections.rotate(child1, lb);
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Collections.rotate(child2, lb);
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return new ChromosomePair(first.newFixedLengthChromosome(child1),
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second.newFixedLengthChromosome(child2));
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}
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}
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@ -0,0 +1,86 @@
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package org.apache.commons.math3.genetics;
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import java.util.Arrays;
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import java.util.HashSet;
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import java.util.Set;
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import org.apache.commons.math3.exception.DimensionMismatchException;
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import org.apache.commons.math3.exception.MathIllegalArgumentException;
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import org.junit.Assert;
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import org.junit.Test;
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public class OrderedCrossoverTest {
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@Test
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public void testCrossover() {
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final Integer[] p1 = new Integer[] { 8, 4, 7, 3, 6, 2, 5, 1, 9, 0 };
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final Integer[] p2 = new Integer[] { 0, 1, 2, 3, 4, 5, 6, 7, 8, 9 };
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final DummyListChromosome p1c = new DummyListChromosome(p1);
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final DummyListChromosome p2c = new DummyListChromosome(p2);
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final CrossoverPolicy cp = new OrderedCrossover<Integer>();
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for (int i = 0; i < 20; i++) {
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final Set<Integer> parentSet1 = new HashSet<Integer>(Arrays.asList(p1));
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final Set<Integer> parentSet2 = new HashSet<Integer>(Arrays.asList(p2));
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final ChromosomePair pair = cp.crossover(p1c, p2c);
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final Integer[] c1 = ((DummyListChromosome) pair.getFirst()).getRepresentation().toArray(new Integer[p1.length]);
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final Integer[] c2 = ((DummyListChromosome) pair.getSecond()).getRepresentation().toArray(new Integer[p2.length]);
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Assert.assertNotSame(p1c, pair.getFirst());
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Assert.assertNotSame(p2c, pair.getSecond());
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// make sure that the children have exactly the same elements as their parents
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for (int j = 0; j < c1.length; j++) {
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Assert.assertTrue(parentSet1.contains(c1[j]));
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parentSet1.remove(c1[j]);
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Assert.assertTrue(parentSet2.contains(c2[j]));
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parentSet2.remove(c2[j]);
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}
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}
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}
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@Test(expected = DimensionMismatchException.class)
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public void testCrossoverDimensionMismatchException() {
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final Integer[] p1 = new Integer[] { 1, 0, 1, 0, 0, 1, 0, 1, 1 };
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final Integer[] p2 = new Integer[] { 0, 1, 1, 0, 1 };
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final BinaryChromosome p1c = new DummyBinaryChromosome(p1);
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final BinaryChromosome p2c = new DummyBinaryChromosome(p2);
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final CrossoverPolicy cp = new OrderedCrossover<Integer>();
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cp.crossover(p1c, p2c);
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}
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@Test(expected = MathIllegalArgumentException.class)
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public void testCrossoverInvalidFixedLengthChromosomeFirst() {
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final Integer[] p1 = new Integer[] { 1, 0, 1, 0, 0, 1, 0, 1, 1 };
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final BinaryChromosome p1c = new DummyBinaryChromosome(p1);
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final Chromosome p2c = new Chromosome() {
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public double fitness() {
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// Not important
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return 0;
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}
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};
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final CrossoverPolicy cp = new OrderedCrossover<Integer>();
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cp.crossover(p1c, p2c);
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}
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@Test(expected = MathIllegalArgumentException.class)
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public void testCrossoverInvalidFixedLengthChromosomeSecond() {
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final Integer[] p1 = new Integer[] { 1, 0, 1, 0, 0, 1, 0, 1, 1 };
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final BinaryChromosome p2c = new DummyBinaryChromosome(p1);
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final Chromosome p1c = new Chromosome() {
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public double fitness() {
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// Not important
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return 0;
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}
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};
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final CrossoverPolicy cp = new OrderedCrossover<Integer>();
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cp.crossover(p1c, p2c);
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}
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}
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