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Diffstat (limited to 'src/main/java/org/apache/commons/math3/genetics/ElitisticListPopulation.java')
-rw-r--r-- | src/main/java/org/apache/commons/math3/genetics/ElitisticListPopulation.java | 125 |
1 files changed, 125 insertions, 0 deletions
diff --git a/src/main/java/org/apache/commons/math3/genetics/ElitisticListPopulation.java b/src/main/java/org/apache/commons/math3/genetics/ElitisticListPopulation.java new file mode 100644 index 0000000..0e7009d --- /dev/null +++ b/src/main/java/org/apache/commons/math3/genetics/ElitisticListPopulation.java @@ -0,0 +1,125 @@ +/* + * 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.NotPositiveException; +import org.apache.commons.math3.exception.NullArgumentException; +import org.apache.commons.math3.exception.NumberIsTooLargeException; +import org.apache.commons.math3.exception.OutOfRangeException; +import org.apache.commons.math3.exception.util.LocalizedFormats; +import org.apache.commons.math3.util.FastMath; + +import java.util.Collections; +import java.util.List; + +/** + * Population of chromosomes which uses elitism (certain percentage of the best chromosomes is + * directly copied to the next generation). + * + * @since 2.0 + */ +public class ElitisticListPopulation extends ListPopulation { + + /** percentage of chromosomes copied to the next generation */ + private double elitismRate = 0.9; + + /** + * Creates a new {@link ElitisticListPopulation} instance. + * + * @param chromosomes list of chromosomes in the population + * @param populationLimit maximal size of the population + * @param elitismRate how many best chromosomes will be directly transferred to the next + * generation [in %] + * @throws NullArgumentException if the list of chromosomes is {@code null} + * @throws NotPositiveException if the population limit is not a positive number (< 1) + * @throws NumberIsTooLargeException if the list of chromosomes exceeds the population limit + * @throws OutOfRangeException if the elitism rate is outside the [0, 1] range + */ + public ElitisticListPopulation( + final List<Chromosome> chromosomes, final int populationLimit, final double elitismRate) + throws NullArgumentException, + NotPositiveException, + NumberIsTooLargeException, + OutOfRangeException { + + super(chromosomes, populationLimit); + setElitismRate(elitismRate); + } + + /** + * Creates a new {@link ElitisticListPopulation} instance and initializes its inner chromosome + * list. + * + * @param populationLimit maximal size of the population + * @param elitismRate how many best chromosomes will be directly transferred to the next + * generation [in %] + * @throws NotPositiveException if the population limit is not a positive number (< 1) + * @throws OutOfRangeException if the elitism rate is outside the [0, 1] range + */ + public ElitisticListPopulation(final int populationLimit, final double elitismRate) + throws NotPositiveException, OutOfRangeException { + + super(populationLimit); + setElitismRate(elitismRate); + } + + /** + * Start the population for the next generation. The <code>{@link #elitismRate}</code> percents + * of the best chromosomes are directly copied to the next generation. + * + * @return the beginnings of the next generation. + */ + public Population nextGeneration() { + // initialize a new generation with the same parameters + ElitisticListPopulation nextGeneration = + new ElitisticListPopulation(getPopulationLimit(), getElitismRate()); + + final List<Chromosome> oldChromosomes = getChromosomeList(); + Collections.sort(oldChromosomes); + + // index of the last "not good enough" chromosome + int boundIndex = (int) FastMath.ceil((1.0 - getElitismRate()) * oldChromosomes.size()); + for (int i = boundIndex; i < oldChromosomes.size(); i++) { + nextGeneration.addChromosome(oldChromosomes.get(i)); + } + return nextGeneration; + } + + /** + * Sets the elitism rate, i.e. how many best chromosomes will be directly transferred to the + * next generation [in %]. + * + * @param elitismRate how many best chromosomes will be directly transferred to the next + * generation [in %] + * @throws OutOfRangeException if the elitism rate is outside the [0, 1] range + */ + public void setElitismRate(final double elitismRate) throws OutOfRangeException { + if (elitismRate < 0 || elitismRate > 1) { + throw new OutOfRangeException(LocalizedFormats.ELITISM_RATE, elitismRate, 0, 1); + } + this.elitismRate = elitismRate; + } + + /** + * Access the elitism rate. + * + * @return the elitism rate + */ + public double getElitismRate() { + return this.elitismRate; + } +} |