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/*
* 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;
}
}
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