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Java example source code file (ElitisticListPopulation.java)

This example Java source code file (ElitisticListPopulation.java) is included in the alvinalexander.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" TM.

Learn more about this Java project at its project page.

Java - Java tags/keywords

elitisticlistpopulation, list, notpositiveexception, nullargumentexception, numberistoolargeexception, outofrangeexception, util

The ElitisticListPopulation.java Java example source code

/*
 * 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 java.util.Collections;
import java.util.List;

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;

/**
 * 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}
     * 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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