Chromosome.java
- /*
- * 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.legacy.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();
- }
- }
- }