| /* |
| * 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.math4.genetics; |
| |
| /** |
| * Individual in a population. Chromosomes are compared based on their fitness. |
| * <p> |
| * The chromosomes are IMMUTABLE, and so their fitness is also immutable and |
| * therefore it can be cached. |
| * |
| * @since 2.0 |
| */ |
| public abstract class Chromosome implements Comparable<Chromosome>,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. |
| * <p> |
| * 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 |
| * <ul> |
| * <li>-1 if <code>another</code> is better than <code>this</code></li> |
| * <li>1 if <code>another</code> is worse than <code>this</code></li> |
| * <li>0 if the two chromosomes have the same fitness</li> |
| * </ul> |
| */ |
| @Override |
| public int compareTo(final Chromosome another) { |
| return Double.compare(getFitness(), another.getFitness()); |
| } |
| |
| /** |
| * Returns <code>true</code> iff <code>another</code> 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 <code>another</code> is equivalent to this chromosome |
| */ |
| protected boolean isSame(final Chromosome another) { |
| return false; |
| } |
| |
| /** |
| * Searches the <code>population</code> for another chromosome with the same representation. If such chromosome is |
| * found, it is returned, if no such chromosome exists, returns <code>null</code>. |
| * |
| * @param population Population to search |
| * @return Chromosome with the same representation, or <code>null</code> 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(); |
| } |
| } |
| |
| } |