001 /* 002 * Licensed to the Apache Software Foundation (ASF) under one or more 003 * contributor license agreements. See the NOTICE file distributed with 004 * this work for additional information regarding copyright ownership. 005 * The ASF licenses this file to You under the Apache License, Version 2.0 006 * (the "License"); you may not use this file except in compliance with 007 * the License. You may obtain a copy of the License at 008 * 009 * http://www.apache.org/licenses/LICENSE-2.0 010 * 011 * Unless required by applicable law or agreed to in writing, software 012 * distributed under the License is distributed on an "AS IS" BASIS, 013 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 014 * See the License for the specific language governing permissions and 015 * limitations under the License. 016 */ 017 package org.apache.commons.math3.genetics; 018 019 import java.util.Collections; 020 import java.util.List; 021 022 import org.apache.commons.math3.exception.NotPositiveException; 023 import org.apache.commons.math3.exception.NullArgumentException; 024 import org.apache.commons.math3.exception.NumberIsTooLargeException; 025 import org.apache.commons.math3.exception.OutOfRangeException; 026 import org.apache.commons.math3.exception.util.LocalizedFormats; 027 import org.apache.commons.math3.util.FastMath; 028 029 /** 030 * Population of chromosomes which uses elitism (certain percentage of the best 031 * chromosomes is directly copied to the next generation). 032 * 033 * @version $Id: ElitisticListPopulation.java 1416643 2012-12-03 19:37:14Z tn $ 034 * @since 2.0 035 */ 036 public class ElitisticListPopulation extends ListPopulation { 037 038 /** percentage of chromosomes copied to the next generation */ 039 private double elitismRate = 0.9; 040 041 /** 042 * Creates a new {@link ElitisticListPopulation} instance. 043 * 044 * @param chromosomes list of chromosomes in the population 045 * @param populationLimit maximal size of the population 046 * @param elitismRate how many best chromosomes will be directly transferred to the next generation [in %] 047 * @throws NullArgumentException if the list of chromosomes is {@code null} 048 * @throws NotPositiveException if the population limit is not a positive number (< 1) 049 * @throws NumberIsTooLargeException if the list of chromosomes exceeds the population limit 050 * @throws OutOfRangeException if the elitism rate is outside the [0, 1] range 051 */ 052 public ElitisticListPopulation(final List<Chromosome> chromosomes, final int populationLimit, 053 final double elitismRate) 054 throws NullArgumentException, NotPositiveException, NumberIsTooLargeException, OutOfRangeException { 055 056 super(chromosomes, populationLimit); 057 setElitismRate(elitismRate); 058 059 } 060 061 /** 062 * Creates a new {@link ElitisticListPopulation} instance and initializes its inner chromosome list. 063 * 064 * @param populationLimit maximal size of the population 065 * @param elitismRate how many best chromosomes will be directly transferred to the next generation [in %] 066 * @throws NotPositiveException if the population limit is not a positive number (< 1) 067 * @throws OutOfRangeException if the elitism rate is outside the [0, 1] range 068 */ 069 public ElitisticListPopulation(final int populationLimit, final double elitismRate) 070 throws NotPositiveException, OutOfRangeException { 071 072 super(populationLimit); 073 setElitismRate(elitismRate); 074 075 } 076 077 /** 078 * Start the population for the next generation. The <code>{@link #elitismRate}</code> 079 * percents of the best chromosomes are directly copied to the next generation. 080 * 081 * @return the beginnings of the next generation. 082 */ 083 public Population nextGeneration() { 084 // initialize a new generation with the same parameters 085 ElitisticListPopulation nextGeneration = 086 new ElitisticListPopulation(getPopulationLimit(), getElitismRate()); 087 088 final List<Chromosome> oldChromosomes = getChromosomeList(); 089 Collections.sort(oldChromosomes); 090 091 // index of the last "not good enough" chromosome 092 int boundIndex = (int) FastMath.ceil((1.0 - getElitismRate()) * oldChromosomes.size()); 093 for (int i = boundIndex; i < oldChromosomes.size(); i++) { 094 nextGeneration.addChromosome(oldChromosomes.get(i)); 095 } 096 return nextGeneration; 097 } 098 099 /** 100 * Sets the elitism rate, i.e. how many best chromosomes will be directly transferred to the next generation [in %]. 101 * 102 * @param elitismRate how many best chromosomes will be directly transferred to the next generation [in %] 103 * @throws OutOfRangeException if the elitism rate is outside the [0, 1] range 104 */ 105 public void setElitismRate(final double elitismRate) throws OutOfRangeException { 106 if (elitismRate < 0 || elitismRate > 1) { 107 throw new OutOfRangeException(LocalizedFormats.ELITISM_RATE, elitismRate, 0, 1); 108 } 109 this.elitismRate = elitismRate; 110 } 111 112 /** 113 * Access the elitism rate. 114 * @return the elitism rate 115 */ 116 public double getElitismRate() { 117 return this.elitismRate; 118 } 119 120 }