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The Apache Commons Math project is a library of lightweight, self-contained mathematics and statistics components addressing the most common practical problems not immediately available in the Java programming language or commons-lang.
/*
* 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.math3.genetics;
/**
* Individual in a population. Chromosomes are compared based on their fitness.
*
* The chromosomes are IMMUTABLE, and so their fitness is also immutable and
* therefore it can be cached.
*
* @since 2.0
* @version $Id: Chromosome.java 1295583 2012-03-01 14:33:03Z erans $
*/
public abstract class Chromosome implements Comparable,Fitness {
/** Value assigned when no fitness has been computed yet. */
private static final double NO_FITNESS = Double.NEGATIVE_INFINITY;
/** Cached value of the fitness of this chromosome. */
private double fitness = NO_FITNESS;
/**
* Access the fitness of this chromosome. The bigger the fitness, the better
* the chromosome.
*
* Computation of fitness is usually very time-consuming task, therefore the
* fitness is cached.
*
* @return the fitness.
*/
public double getFitness() {
if (this.fitness == NO_FITNESS) {
// no cache - compute the fitness
this.fitness = fitness();
}
return this.fitness;
}
/**
* Compares two chromosomes based on their fitness. The bigger the fitness,
* the better the chromosome.
*
* @param another another chromosome to compare
* @return
*
* - -1 if
another is better than this
* - 1 if
another is worse than this
* - 0 if the two chromosomes have the same fitness
*
*/
public int compareTo(final Chromosome another) {
return ((Double)this.getFitness()).compareTo(another.getFitness());
}
/**
* Returns true iff another has the same
* representation and therefore the same fitness. By default, it returns
* false -- override it in your implementation if you need it.
* @param another chromosome to compare
* @return true if another is equivalent to this chromosome
*/
protected boolean isSame(final Chromosome another) {
return false;
}
/**
* Searches the population for another chromosome with the same
* representation. If such chromosome is found, it is returned, if no such
* chromosome exists, returns null.
*
* @param population Population to search
* @return Chromosome with the same representation, or null if
* no such chromosome exists.
*/
protected Chromosome findSameChromosome(final Population population) {
for (Chromosome anotherChr : population) {
if (this.isSame(anotherChr)) {
return anotherChr;
}
}
return null;
}
/**
* Searches the population for a chromosome representing the same solution,
* and if it finds one, updates the fitness to its value.
*
* @param population Population to search
*/
public void searchForFitnessUpdate(final Population population) {
Chromosome sameChromosome = findSameChromosome(population);
if (sameChromosome != null) {
fitness = sameChromosome.getFitness();
}
}
}