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 /** 020 * Individual in a population. Chromosomes are compared based on their fitness. 021 * <p> 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 $Id: Chromosome.java 1416643 2012-12-03 19:37:14Z tn $ 027 */ 028 public abstract class Chromosome implements Comparable<Chromosome>,Fitness { 029 /** Value assigned when no fitness has been computed yet. */ 030 private static final double NO_FITNESS = Double.NEGATIVE_INFINITY; 031 032 /** Cached value of the fitness of this chromosome. */ 033 private double fitness = NO_FITNESS; 034 035 /** 036 * Access the fitness of this chromosome. The bigger the fitness, the better the chromosome. 037 * <p> 038 * Computation of fitness is usually very time-consuming task, therefore the fitness is cached. 039 * 040 * @return the fitness 041 */ 042 public double getFitness() { 043 if (this.fitness == NO_FITNESS) { 044 // no cache - compute the fitness 045 this.fitness = fitness(); 046 } 047 return this.fitness; 048 } 049 050 /** 051 * Compares two chromosomes based on their fitness. The bigger the fitness, the better the chromosome. 052 * 053 * @param another another chromosome to compare 054 * @return 055 * <ul> 056 * <li>-1 if <code>another</code> is better than <code>this</code></li> 057 * <li>1 if <code>another</code> is worse than <code>this</code></li> 058 * <li>0 if the two chromosomes have the same fitness</li> 059 * </ul> 060 */ 061 public int compareTo(final Chromosome another) { 062 return ((Double)this.getFitness()).compareTo(another.getFitness()); 063 } 064 065 /** 066 * Returns <code>true</code> iff <code>another</code> has the same representation and therefore the same fitness. By 067 * default, it returns false -- override it in your implementation if you need it. 068 * 069 * @param another chromosome to compare 070 * @return true if <code>another</code> is equivalent to this chromosome 071 */ 072 protected boolean isSame(final Chromosome another) { 073 return false; 074 } 075 076 /** 077 * Searches the <code>population</code> for another chromosome with the same representation. If such chromosome is 078 * found, it is returned, if no such chromosome exists, returns <code>null</code>. 079 * 080 * @param population Population to search 081 * @return Chromosome with the same representation, or <code>null</code> if no such chromosome exists. 082 */ 083 protected Chromosome findSameChromosome(final Population population) { 084 for (Chromosome anotherChr : population) { 085 if (this.isSame(anotherChr)) { 086 return anotherChr; 087 } 088 } 089 return null; 090 } 091 092 /** 093 * Searches the population for a chromosome representing the same solution, and if it finds one, 094 * updates the fitness to its value. 095 * 096 * @param population Population to search 097 */ 098 public void searchForFitnessUpdate(final Population population) { 099 Chromosome sameChromosome = findSameChromosome(population); 100 if (sameChromosome != null) { 101 fitness = sameChromosome.getFitness(); 102 } 103 } 104 105 }