1 | /*
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2 | * Licensed to the Apache Software Foundation (ASF) under one or more
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3 | * contributor license agreements. See the NOTICE file distributed with
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4 | * this work for additional information regarding copyright ownership.
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5 | * The ASF licenses this file to You under the Apache License, Version 2.0
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6 | * (the "License"); you may not use this file except in compliance with
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7 | * the License. You may obtain a copy of the License at
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8 | *
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9 | * http://www.apache.org/licenses/LICENSE-2.0
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10 | *
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11 | * Unless required by applicable law or agreed to in writing, software
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12 | * distributed under the License is distributed on an "AS IS" BASIS,
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13 | * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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14 | * See the License for the specific language governing permissions and
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15 | * limitations under the License.
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16 | */
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17 | package agents.anac.y2019.harddealer.math3.genetics;
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18 |
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19 | import java.util.ArrayList;
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20 | import java.util.List;
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21 |
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22 | import agents.anac.y2019.harddealer.math3.exception.MathIllegalArgumentException;
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23 | import agents.anac.y2019.harddealer.math3.exception.util.LocalizedFormats;
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24 |
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25 | /**
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26 | * Tournament selection scheme. Each of the two selected chromosomes is selected
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27 | * based on n-ary tournament -- this is done by drawing {@link #arity} random
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28 | * chromosomes without replacement from the population, and then selecting the
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29 | * fittest chromosome among them.
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30 | *
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31 | * @since 2.0
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32 | */
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33 | public class TournamentSelection implements SelectionPolicy {
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34 |
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35 | /** number of chromosomes included in the tournament selections */
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36 | private int arity;
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37 |
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38 | /**
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39 | * Creates a new TournamentSelection instance.
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40 | *
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41 | * @param arity how many chromosomes will be drawn to the tournament
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42 | */
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43 | public TournamentSelection(final int arity) {
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44 | this.arity = arity;
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45 | }
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46 |
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47 | /**
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48 | * Select two chromosomes from the population. Each of the two selected
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49 | * chromosomes is selected based on n-ary tournament -- this is done by
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50 | * drawing {@link #arity} random chromosomes without replacement from the
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51 | * population, and then selecting the fittest chromosome among them.
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52 | *
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53 | * @param population the population from which the chromosomes are chosen.
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54 | * @return the selected chromosomes.
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55 | * @throws MathIllegalArgumentException if the tournament arity is bigger than the population size
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56 | */
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57 | public ChromosomePair select(final Population population) throws MathIllegalArgumentException {
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58 | return new ChromosomePair(tournament((ListPopulation) population),
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59 | tournament((ListPopulation) population));
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60 | }
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61 |
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62 | /**
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63 | * Helper for {@link #select(Population)}. Draw {@link #arity} random chromosomes without replacement from the
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64 | * population, and then select the fittest chromosome among them.
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65 | *
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66 | * @param population the population from which the chromosomes are chosen.
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67 | * @return the selected chromosome.
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68 | * @throws MathIllegalArgumentException if the tournament arity is bigger than the population size
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69 | */
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70 | private Chromosome tournament(final ListPopulation population) throws MathIllegalArgumentException {
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71 | if (population.getPopulationSize() < this.arity) {
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72 | throw new MathIllegalArgumentException(LocalizedFormats.TOO_LARGE_TOURNAMENT_ARITY,
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73 | arity, population.getPopulationSize());
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74 | }
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75 | // auxiliary population
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76 | ListPopulation tournamentPopulation = new ListPopulation(this.arity) {
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77 | /** {@inheritDoc} */
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78 | public Population nextGeneration() {
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79 | // not useful here
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80 | return null;
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81 | }
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82 | };
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83 |
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84 | // create a copy of the chromosome list
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85 | List<Chromosome> chromosomes = new ArrayList<Chromosome> (population.getChromosomes());
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86 | for (int i=0; i<this.arity; i++) {
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87 | // select a random individual and add it to the tournament
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88 | int rind = GeneticAlgorithm.getRandomGenerator().nextInt(chromosomes.size());
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89 | tournamentPopulation.addChromosome(chromosomes.get(rind));
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90 | // do not select it again
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91 | chromosomes.remove(rind);
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92 | }
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93 | // the winner takes it all
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94 | return tournamentPopulation.getFittestChromosome();
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95 | }
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96 |
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97 | /**
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98 | * Gets the arity (number of chromosomes drawn to the tournament).
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99 | *
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100 | * @return arity of the tournament
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101 | */
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102 | public int getArity() {
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103 | return arity;
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104 | }
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105 |
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106 | /**
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107 | * Sets the arity (number of chromosomes drawn to the tournament).
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108 | *
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109 | * @param arity arity of the tournament
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110 | */
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111 | public void setArity(final int arity) {
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112 | this.arity = arity;
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113 | }
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114 |
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115 | }
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