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


public class FitnessCachingTest {

    // parameters for the GA
    private static final int DIMENSION = 50;
    private static final double CROSSOVER_RATE = 1;
    private static final double MUTATION_RATE = 0.1;
    private static final int TOURNAMENT_ARITY = 5;

    private static final int POPULATION_SIZE = 10;
    private static final int NUM_GENERATIONS = 50;
    private static final double ELITISM_RATE = 0.2;

    // how many times was the fitness computed
    private static int fitnessCalls = 0;


    @Test
    public void testFitnessCaching() {
        // 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, // no mutation
                new TournamentSelection(TOURNAMENT_ARITY)
        );

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

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

        int neededCalls =
            POPULATION_SIZE /*initial population*/ +
            (NUM_GENERATIONS - 1) /*for each population*/ * (int)(POPULATION_SIZE * (1.0 - ELITISM_RATE)) /*some chromosomes are copied*/
            ;
        Assert.assertTrue(fitnessCalls <= neededCalls); // some chromosomes after crossover may be the same os old ones
    }


    /**
     * 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 DummyCountingBinaryChromosome(BinaryChromosome.randomBinaryRepresentation(DIMENSION));
            popList.add(randChrom);
        }
        return new ElitisticListPopulation(popList, popList.size(), ELITISM_RATE);
    }

    private static class DummyCountingBinaryChromosome extends DummyBinaryChromosome {

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

        @Override
        public double fitness() {
            fitnessCalls++;
            return 0;
        }
    }
}