src/test/java/org/apache/commons/math3/genetics/GeneticAlgorithmTestBinary.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.math3.genetics;


import java.util.LinkedList;
import java.util.List;

import org.junit.Assert;
import org.junit.Test;

/**
 * This is also an example of usage.
 */
public class GeneticAlgorithmTestBinary {

    // parameters for the GA
    private static final int DIMENSION = 50;
    private static final int POPULATION_SIZE = 50;
    private static final int NUM_GENERATIONS = 50;
    private static final double ELITISM_RATE = 0.2;
    private static final double CROSSOVER_RATE = 1;
    private static final double MUTATION_RATE = 0.1;
    private static final int TOURNAMENT_ARITY = 2;

    @Test
    public void test() {
        // to test a stochastic algorithm is hard, so this will rather be an usage example

        // initialize a new genetic algorithm
        GeneticAlgorithm ga = new GeneticAlgorithm(
                new OnePointCrossover<Integer>(),
                CROSSOVER_RATE, // all selected chromosomes will be recombined (=crosssover)
                new BinaryMutation(),
                MUTATION_RATE,
                new TournamentSelection(TOURNAMENT_ARITY)
        );

        Assert.assertEquals(0, ga.getGenerationsEvolved());

        // initial population
        Population initial = randomPopulation();
        // stopping conditions
        StoppingCondition stopCond = new FixedGenerationCount(NUM_GENERATIONS);

        // best initial chromosome
        Chromosome bestInitial = initial.getFittestChromosome();

        // run the algorithm
        Population finalPopulation = ga.evolve(initial, stopCond);

        // best chromosome from the final population
        Chromosome bestFinal = finalPopulation.getFittestChromosome();

        // the only thing we can test is whether the final solution is not worse than the initial one
        // however, for some implementations of GA, this need not be true :)

        Assert.assertTrue(bestFinal.compareTo(bestInitial) > 0);
        Assert.assertEquals(NUM_GENERATIONS, ga.getGenerationsEvolved());

    }




    /**
     * Initializes a random population.
     */
    private static ElitisticListPopulation randomPopulation() {
        List<Chromosome> popList = new LinkedList<Chromosome>();

        for (int i=0; i<POPULATION_SIZE; i++) {
            BinaryChromosome randChrom = new FindOnes(BinaryChromosome.randomBinaryRepresentation(DIMENSION));
            popList.add(randChrom);
        }
        return new ElitisticListPopulation(popList, popList.size(), ELITISM_RATE);
    }

    /**
     * Chromosomes represented by a binary chromosome.
     *
     * The goal is to set all bits (genes) to 1.
     */
    private static class FindOnes extends BinaryChromosome {

        public FindOnes(List<Integer> representation) {
            super(representation);
        }

        /**
         * Returns number of elements != 0
         */
        public double fitness() {
            int num = 0;
            for (int val : this.getRepresentation()) {
                if (val != 0)
                    num++;
            }
            // number of elements >= 0
            return num;
        }

        @Override
        public AbstractListChromosome<Integer> newFixedLengthChromosome(List<Integer> chromosomeRepresentation) {
            return new FindOnes(chromosomeRepresentation);
        }

    }
}