Raymond | dee0849 | 2015-04-02 10:43:13 -0700 | [diff] [blame] | 1 | /* |
| 2 | * Licensed to the Apache Software Foundation (ASF) under one or more |
| 3 | * contributor license agreements. See the NOTICE file distributed with |
| 4 | * this work for additional information regarding copyright ownership. |
| 5 | * The ASF licenses this file to You under the Apache License, Version 2.0 |
| 6 | * (the "License"); you may not use this file except in compliance with |
| 7 | * the License. You may obtain a copy of the License at |
| 8 | * |
| 9 | * http://www.apache.org/licenses/LICENSE-2.0 |
| 10 | * |
| 11 | * Unless required by applicable law or agreed to in writing, software |
| 12 | * distributed under the License is distributed on an "AS IS" BASIS, |
| 13 | * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. |
| 14 | * See the License for the specific language governing permissions and |
| 15 | * limitations under the License. |
| 16 | */ |
| 17 | package org.apache.commons.math.genetics; |
| 18 | |
| 19 | /** |
| 20 | * Individual in a population. Chromosomes are compared based on their fitness. |
| 21 | * |
| 22 | * The chromosomes are IMMUTABLE, and so their fitness is also immutable and |
| 23 | * therefore it can be cached. |
| 24 | * |
| 25 | * @since 2.0 |
| 26 | * @version $Revision: 811685 $ $Date: 2009-09-05 19:36:48 +0200 (sam. 05 sept. 2009) $ |
| 27 | */ |
| 28 | public abstract class Chromosome implements Comparable<Chromosome>,Fitness { |
| 29 | |
| 30 | /** |
| 31 | * Cached value of the fitness of this chromosome. |
| 32 | */ |
| 33 | private double fitness = Double.MIN_VALUE; |
| 34 | |
| 35 | /** |
| 36 | * Access the fitness of this chromosome. The bigger the fitness, the better |
| 37 | * the chromosome. |
| 38 | * |
| 39 | * Computation of fitness is usually very time-consuming task, therefore the |
| 40 | * fitness is cached. |
| 41 | * |
| 42 | * @return the fitness. |
| 43 | */ |
| 44 | public double getFitness() { |
| 45 | if (this.fitness == Double.MIN_VALUE) { |
| 46 | // no cache - compute the fitness |
| 47 | this.fitness = fitness(); |
| 48 | } |
| 49 | return this.fitness; |
| 50 | } |
| 51 | |
| 52 | /** |
| 53 | * Compares two chromosomes based on their fitness. The bigger the fitness, |
| 54 | * the better the chromosome. |
| 55 | * |
| 56 | * @param another another chromosome to compare |
| 57 | * @return |
| 58 | * <ul> |
| 59 | * <li>-1 if <code>another</code> is better than <code>this</code></li> |
| 60 | * <li>1 if <code>another</code> is worse than <code>this</code></li> |
| 61 | * <li>0 if the two chromosomes have the same fitness</li> |
| 62 | * </ul> |
| 63 | */ |
| 64 | public int compareTo(Chromosome another) { |
| 65 | return ((Double)this.getFitness()).compareTo(another.getFitness()); |
| 66 | } |
| 67 | |
| 68 | /** |
| 69 | * Returns <code>true<code> iff <code>another</code> has the same |
| 70 | * representation and therefore the same fitness. By default, it returns |
| 71 | * false -- override it in your implementation if you need it. |
| 72 | * @param another chromosome to compare |
| 73 | * @return true if <code>another</code> is equivalent to this chromosome |
| 74 | */ |
| 75 | protected boolean isSame(Chromosome another) { |
| 76 | return false; |
| 77 | } |
| 78 | |
| 79 | /** |
| 80 | * Searches the <code>population</code> for another chromosome with the same |
| 81 | * representation. If such chromosome is found, it is returned, if no such |
| 82 | * chromosome exists, returns <code>null</code>. |
| 83 | * |
| 84 | * @param population |
| 85 | * Population to search |
| 86 | * @return Chromosome with the same representation, or <code>null</code> if |
| 87 | * no such chromosome exists. |
| 88 | */ |
| 89 | protected Chromosome findSameChromosome(Population population) { |
| 90 | for (Chromosome anotherChr : population) { |
| 91 | if (this.isSame(anotherChr)) |
| 92 | return anotherChr; |
| 93 | } |
| 94 | return null; |
| 95 | } |
| 96 | |
| 97 | /** |
| 98 | * Searches the population for a chromosome representing the same solution, |
| 99 | * 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 | } |