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 | /**
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20 | * Individual in a population. Chromosomes are compared based on their fitness.
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21 | * <p>
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22 | * The chromosomes are IMMUTABLE, and so their fitness is also immutable and
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23 | * therefore it can be cached.
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24 | *
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25 | * @since 2.0
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26 | */
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27 | public abstract class Chromosome implements Comparable<Chromosome>,Fitness {
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28 | /** Value assigned when no fitness has been computed yet. */
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29 | private static final double NO_FITNESS = Double.NEGATIVE_INFINITY;
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30 |
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31 | /** Cached value of the fitness of this chromosome. */
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32 | private double fitness = NO_FITNESS;
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33 |
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34 | /**
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35 | * Access the fitness of this chromosome. The bigger the fitness, the better the chromosome.
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36 | * <p>
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37 | * Computation of fitness is usually very time-consuming task, therefore the fitness is cached.
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38 | *
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39 | * @return the fitness
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40 | */
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41 | public double getFitness() {
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42 | if (this.fitness == NO_FITNESS) {
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43 | // no cache - compute the fitness
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44 | this.fitness = fitness();
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45 | }
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46 | return this.fitness;
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47 | }
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48 |
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49 | /**
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50 | * Compares two chromosomes based on their fitness. The bigger the fitness, the better the chromosome.
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51 | *
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52 | * @param another another chromosome to compare
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53 | * @return
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54 | * <ul>
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55 | * <li>-1 if <code>another</code> is better than <code>this</code></li>
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56 | * <li>1 if <code>another</code> is worse than <code>this</code></li>
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57 | * <li>0 if the two chromosomes have the same fitness</li>
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58 | * </ul>
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59 | */
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60 | public int compareTo(final Chromosome another) {
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61 | return Double.compare(getFitness(), another.getFitness());
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62 | }
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63 |
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64 | /**
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65 | * Returns <code>true</code> iff <code>another</code> has the same representation and therefore the same fitness. By
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66 | * default, it returns false -- override it in your implementation if you need it.
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67 | *
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68 | * @param another chromosome to compare
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69 | * @return true if <code>another</code> is equivalent to this chromosome
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70 | */
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71 | protected boolean isSame(final Chromosome another) {
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72 | return false;
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73 | }
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74 |
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75 | /**
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76 | * Searches the <code>population</code> for another chromosome with the same representation. If such chromosome is
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77 | * found, it is returned, if no such chromosome exists, returns <code>null</code>.
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78 | *
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79 | * @param population Population to search
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80 | * @return Chromosome with the same representation, or <code>null</code> if no such chromosome exists.
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81 | */
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82 | protected Chromosome findSameChromosome(final Population population) {
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83 | for (Chromosome anotherChr : population) {
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84 | if (this.isSame(anotherChr)) {
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85 | return anotherChr;
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86 | }
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87 | }
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88 | return null;
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89 | }
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90 |
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91 | /**
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92 | * Searches the population for a chromosome representing the same solution, and if it finds one,
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93 | * updates the fitness to its value.
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94 | *
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95 | * @param population Population to search
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96 | */
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97 | public void searchForFitnessUpdate(final Population population) {
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98 | Chromosome sameChromosome = findSameChromosome(population);
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99 | if (sameChromosome != null) {
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100 | fitness = sameChromosome.getFitness();
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101 | }
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102 | }
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103 |
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104 | }
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