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* The ASF licenses this file to You under the Apache License, Version 2.0
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* http://www.apache.org/licenses/LICENSE-2.0
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* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
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package org.apache.commons.math3.genetics;
import java.util.ArrayList;
import java.util.List;
import org.apache.commons.math3.exception.DimensionMismatchException;
import org.apache.commons.math3.exception.MathIllegalArgumentException;
import org.apache.commons.math3.exception.NotStrictlyPositiveException;
import org.apache.commons.math3.exception.NumberIsTooLargeException;
import org.apache.commons.math3.exception.util.LocalizedFormats;
import org.apache.commons.math3.random.RandomGenerator;
N-point crossover policy. For each iteration 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.
Example (2-point crossover):
-C- denotes a crossover point
-C- -C- -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 VV (*) VV
/----\ /--------\ /-----\ /----\ /--------\ /-----\
c1 = (1 0 | 1 0 1 0 | 0 1 1) X c2 = (0 1 | 1 0 0 1 | 0 1 1)
This policy works only on AbstractListChromosome, and therefore it is parameterized by T. Moreover, the chromosomes must have same lengths. Type parameters: - <T> – generic type of the
AbstractListChromosomes for crossover
Since: 3.1
/**
* N-point crossover policy. For each iteration 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.
*
* Example (2-point crossover):
* <pre>
* -C- denotes a crossover point
* -C- -C- -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 VV (*) VV
* /----\ /--------\ /-----\ /----\ /--------\ /-----\
* c1 = (1 0 | 1 0 1 0 | 0 1 1) X c2 = (0 1 | 1 0 0 1 | 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 3.1
*/
public class NPointCrossover<T> implements CrossoverPolicy {
The number of crossover points. /** The number of crossover points. */
private final int crossoverPoints;
Creates a new NPointCrossover policy using the given number of points.
Note: the number of crossover points must be < chromosome length - 1.
This condition can only be checked at runtime, as the chromosome length is not known in advance.
Params: - crossoverPoints – the number of crossover points
Throws: - NotStrictlyPositiveException – if the number of
crossoverPoints is not strictly positive
/**
* Creates a new {@link NPointCrossover} policy using the given number of points.
* <p>
* <b>Note</b>: the number of crossover points must be < <code>chromosome length - 1</code>.
* This condition can only be checked at runtime, as the chromosome length is not known in advance.
*
* @param crossoverPoints the number of crossover points
* @throws NotStrictlyPositiveException if the number of {@code crossoverPoints} is not strictly positive
*/
public NPointCrossover(final int crossoverPoints) throws NotStrictlyPositiveException {
if (crossoverPoints <= 0) {
throw new NotStrictlyPositiveException(crossoverPoints);
}
this.crossoverPoints = crossoverPoints;
}
Returns the number of crossover points used by this CrossoverPolicy. Returns: the number of crossover points
/**
* Returns the number of crossover points used by this {@link CrossoverPolicy}.
*
* @return the number of crossover points
*/
public int getCrossoverPoints() {
return crossoverPoints;
}
Performs a N-point crossover. N random crossover points are selected and are used
to divide the parent chromosomes into segments. The segments are copied in alternate
order from the two parents to the corresponding child chromosomes.
Example (2-point crossover):
-C- denotes a crossover point
-C- -C- -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 VV (*) VV
/----\ /--------\ /-----\ /----\ /--------\ /-----\
c1 = (1 0 | 1 0 1 0 | 0 1 1) X c2 = (0 1 | 1 0 0 1 | 0 1 1)
Params: - first – first parent (p1)
- second – second parent (p2)
Throws: - MathIllegalArgumentException – iff one of the chromosomes is not an instance of
AbstractListChromosome - DimensionMismatchException – if the length of the two chromosomes is different
Returns: pair of two children (c1,c2)
/**
* Performs a N-point crossover. N random crossover points are selected and are used
* to divide the parent chromosomes into segments. The segments are copied in alternate
* order from the two parents to the corresponding child chromosomes.
*
* Example (2-point crossover):
* <pre>
* -C- denotes a crossover point
* -C- -C- -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 VV (*) VV
* /----\ /--------\ /-----\ /----\ /--------\ /-----\
* c1 = (1 0 | 1 0 1 0 | 0 1 1) X c2 = (0 1 | 1 0 0 1 | 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 mate((AbstractListChromosome<T>) first, (AbstractListChromosome<T>) second);
}
Helper for crossover(Chromosome, Chromosome). Performs the actual crossover. Params: - first – the first chromosome
- second – the second chromosome
Throws: - DimensionMismatchException – if the length of the two chromosomes is different
- NumberIsTooLargeException – if the number of crossoverPoints is too large for the actual chromosomes
Returns: the pair of new chromosomes that resulted from the crossover
/**
* 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
* @throws NumberIsTooLargeException if the number of crossoverPoints is too large for the actual chromosomes
*/
private ChromosomePair mate(final AbstractListChromosome<T> first,
final AbstractListChromosome<T> second)
throws DimensionMismatchException, NumberIsTooLargeException {
final int length = first.getLength();
if (length != second.getLength()) {
throw new DimensionMismatchException(second.getLength(), length);
}
if (crossoverPoints >= length) {
throw new NumberIsTooLargeException(crossoverPoints, length, false);
}
// 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);
final RandomGenerator random = GeneticAlgorithm.getRandomGenerator();
List<T> c1 = child1Rep;
List<T> c2 = child2Rep;
int remainingPoints = crossoverPoints;
int lastIndex = 0;
for (int i = 0; i < crossoverPoints; i++, remainingPoints--) {
// select the next crossover point at random
final int crossoverIndex = 1 + lastIndex + random.nextInt(length - lastIndex - remainingPoints);
// copy the current segment
for (int j = lastIndex; j < crossoverIndex; j++) {
c1.add(parent1Rep.get(j));
c2.add(parent2Rep.get(j));
}
// swap the children for the next segment
List<T> tmp = c1;
c1 = c2;
c2 = tmp;
lastIndex = crossoverIndex;
}
// copy the last segment
for (int j = lastIndex; j < length; j++) {
c1.add(parent1Rep.get(j));
c2.add(parent2Rep.get(j));
}
return new ChromosomePair(first.newFixedLengthChromosome(child1Rep),
second.newFixedLengthChromosome(child2Rep));
}
}