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.math.genetics; 018 019 /** 020 * Individual in a population. Chromosomes are compared based on their fitness. 021 * 022 * The chromosomes are IMMUTABLE, and so their fitness is also immutable and 023 * therefore it can be cached. 024 * 025 * @since 2.0 026 * @version $Revision: 811685 $ $Date: 2009-09-05 13:36:48 -0400 (Sat, 05 Sep 2009) $ 027 */ 028 public abstract class Chromosome implements Comparable<Chromosome>,Fitness { 029 030 /** 031 * Cached value of the fitness of this chromosome. 032 */ 033 private double fitness = Double.MIN_VALUE; 034 035 /** 036 * Access the fitness of this chromosome. The bigger the fitness, the better 037 * the chromosome. 038 * 039 * Computation of fitness is usually very time-consuming task, therefore the 040 * fitness is cached. 041 * 042 * @return the fitness. 043 */ 044 public double getFitness() { 045 if (this.fitness == Double.MIN_VALUE) { 046 // no cache - compute the fitness 047 this.fitness = fitness(); 048 } 049 return this.fitness; 050 } 051 052 /** 053 * Compares two chromosomes based on their fitness. The bigger the fitness, 054 * the better the chromosome. 055 * 056 * @param another another chromosome to compare 057 * @return 058 * <ul> 059 * <li>-1 if <code>another</code> is better than <code>this</code></li> 060 * <li>1 if <code>another</code> is worse than <code>this</code></li> 061 * <li>0 if the two chromosomes have the same fitness</li> 062 * </ul> 063 */ 064 public int compareTo(Chromosome another) { 065 return ((Double)this.getFitness()).compareTo(another.getFitness()); 066 } 067 068 /** 069 * Returns <code>true<code> iff <code>another</code> has the same 070 * representation and therefore the same fitness. By default, it returns 071 * false -- override it in your implementation if you need it. 072 * @param another chromosome to compare 073 * @return true if <code>another</code> is equivalent to this chromosome 074 */ 075 protected boolean isSame(Chromosome another) { 076 return false; 077 } 078 079 /** 080 * Searches the <code>population</code> for another chromosome with the same 081 * representation. If such chromosome is found, it is returned, if no such 082 * chromosome exists, returns <code>null</code>. 083 * 084 * @param population 085 * Population to search 086 * @return Chromosome with the same representation, or <code>null</code> if 087 * no such chromosome exists. 088 */ 089 protected Chromosome findSameChromosome(Population population) { 090 for (Chromosome anotherChr : population) { 091 if (this.isSame(anotherChr)) 092 return anotherChr; 093 } 094 return null; 095 } 096 097 /** 098 * Searches the population for a chromosome representing the same solution, 099 * and if it finds one, updates the fitness to its value. 100 * 101 * @param population 102 * Population to search 103 */ 104 public void searchForFitnessUpdate(Population population) { 105 Chromosome sameChromosome = findSameChromosome(population); 106 if (sameChromosome != null) { 107 fitness = sameChromosome.getFitness(); 108 } 109 } 110 111 }