| /* |
| * 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.math.genetics; |
| |
| import java.util.Collections; |
| import java.util.List; |
| |
| import org.apache.commons.math.util.FastMath; |
| |
| /** |
| * Population of chromosomes which uses elitism (certain percentace of the best |
| * chromosomes is directly copied to the next generation). |
| * |
| * @version $Revision: 990655 $ $Date: 2010-08-29 23:49:40 +0200 (dim. 29 août 2010) $ |
| * @since 2.0 |
| */ |
| public class ElitisticListPopulation extends ListPopulation { |
| |
| /** percentage of chromosomes copied to the next generation */ |
| private double elitismRate = 0.9; |
| |
| /** |
| * Creates a new 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 %] |
| */ |
| public ElitisticListPopulation(List<Chromosome> chromosomes, int populationLimit, double elitismRate) { |
| super(chromosomes, populationLimit); |
| this.elitismRate = elitismRate; |
| } |
| |
| /** |
| * Creates a new ListPopulation 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 %] |
| */ |
| public ElitisticListPopulation(int populationLimit, double elitismRate) { |
| super(populationLimit); |
| this.elitismRate = 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(this.getPopulationLimit(), this.getElitismRate()); |
| |
| List<Chromosome> oldChromosomes = this.getChromosomes(); |
| Collections.sort(oldChromosomes); |
| |
| // index of the last "not good enough" chromosome |
| int boundIndex = (int) FastMath.ceil((1.0 - this.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 %] |
| */ |
| public void setElitismRate(double elitismRate) { |
| if (elitismRate < 0 || elitismRate > 1) |
| throw new IllegalArgumentException("Elitism rate has to be in [0,1]"); |
| this.elitismRate = elitismRate; |
| } |
| |
| /** |
| * Access the elitism rate. |
| * @return the elitism rate |
| */ |
| public double getElitismRate() { |
| return this.elitismRate; |
| } |
| |
| } |