[14429] | 1 | #region License Information
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| 2 | /* HeuristicLab
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| 3 | * Copyright (C) 2002-2016 Heuristic and Evolutionary Algorithms Laboratory (HEAL)
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| 4 | *
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| 5 | * This file is part of HeuristicLab.
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| 6 | *
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| 7 | * HeuristicLab is free software: you can redistribute it and/or modify
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| 8 | * it under the terms of the GNU General Public License as published by
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| 9 | * the Free Software Foundation, either version 3 of the License, or
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| 10 | * (at your option) any later version.
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| 11 | *
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| 12 | * HeuristicLab is distributed in the hope that it will be useful,
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| 13 | * but WITHOUT ANY WARRANTY; without even the implied warranty of
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| 14 | * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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| 15 | * GNU General Public License for more details.
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| 16 | *
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| 17 | * You should have received a copy of the GNU General Public License
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| 18 | * along with HeuristicLab. If not, see <http://www.gnu.org/licenses/>.
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| 19 | */
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| 20 | #endregion
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| 21 |
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| 22 | using System;
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| 23 | using System.Linq;
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| 24 | using System.Threading;
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| 25 | using HeuristicLab.Common;
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| 26 | using HeuristicLab.Core;
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| 27 | using HeuristicLab.Optimization;
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| 28 | using HeuristicLab.Persistence.Default.CompositeSerializers.Storable;
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| 29 | using HeuristicLab.Random;
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| 30 |
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| 31 | namespace HeuristicLab.Encodings.BinaryVectorEncoding.LocalSearch {
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| 32 | [Item("Exhaustive Bitflip Local Search (binary)", "", ExcludeGenericTypeInfo = true)]
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| 33 | [StorableClass]
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| 34 | public class ExhaustiveBitflip<TProblem, TContext> : NamedItem, IBinaryLocalSearch<TContext>
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| 35 | where TProblem : class, ISingleObjectiveProblemDefinition<BinaryVectorEncoding, BinaryVector>, ISingleObjectiveProblem<BinaryVectorEncoding, BinaryVector> // need both, because one has Maximization, the other only the IParameter
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| 36 | where TContext : IProblemContext<TProblem, BinaryVectorEncoding, BinaryVector>,
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| 37 | ISingleObjectiveSolutionContext<BinaryVector>, IStochasticContext,
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| 38 | IEvaluatedSolutionsContext, ILongRunningOperationContext {
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| 39 |
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| 40 | public override bool CanChangeName {
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| 41 | get { return false; }
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| 42 | }
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| 43 | public override bool CanChangeDescription {
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| 44 | get { return false; }
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| 45 | }
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| 46 |
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| 47 | [StorableConstructor]
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| 48 | protected ExhaustiveBitflip(bool deserializing) : base(deserializing) { }
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| 49 | protected ExhaustiveBitflip(ExhaustiveBitflip<TProblem, TContext> original, Cloner cloner) : base(original, cloner) { }
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| 50 | public ExhaustiveBitflip() : base() {
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| 51 | name = ItemName;
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| 52 | description = ItemDescription;
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| 53 | }
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| 54 |
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| 55 | public override IDeepCloneable Clone(Cloner cloner) {
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| 56 | return new ExhaustiveBitflip<TProblem, TContext>(this, cloner);
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| 57 | }
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| 58 |
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| 59 | public void Optimize(TContext context) {
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| 60 | var quality = context.Solution.Fitness;
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| 61 | try {
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| 62 | var result = Search(context.Random, context.Solution.Solution, ref quality,
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| 63 | context.Problem.Maximization, context.Problem.Evaluate, context.CancellationToken);
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| 64 | context.IncEvaluatedSolutions(result.Item1);
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| 65 | var stepsContext = context as IImprovementStepsContext;
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| 66 | if (stepsContext != null)
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| 67 | stepsContext.ImprovementSteps = result.Item2;
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| 68 | } finally {
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| 69 | context.Solution.Fitness = quality;
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| 70 | }
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| 71 | }
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| 72 |
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| 73 | private static bool IsBetter(bool maximization, double a, double b) {
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| 74 | return maximization && a > b
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| 75 | || !maximization && a < b;
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| 76 | }
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| 77 |
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| 78 | public static Tuple<int, int> Search(IRandom random, BinaryVector solution, ref double quality, bool maximization, Func<BinaryVector, IRandom, double> evalFunc, CancellationToken token, bool[] subspace = null) {
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| 79 | if (double.IsNaN(quality)) quality = evalFunc(solution, null);
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| 80 | var improved = false;
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| 81 | var order = Enumerable.Range(0, solution.Length).Shuffle(random).ToArray();
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| 82 | var lastImp = -1;
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| 83 | var steps = 0;
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| 84 | var evaluations = 0;
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| 85 | do {
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| 86 | improved = false;
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| 87 | for (var i = 0; i < solution.Length; i++) {
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| 88 | // in case we didn't make an improvement this round and arrived at the index of the last improvement
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| 89 | // break means we don't need to try the remaining moves again as they have brought no improvement
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| 90 | if (!improved && lastImp == i) break;
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| 91 | var idx = order[i];
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| 92 | if (subspace != null && !subspace[idx]) continue;
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| 93 | // bitflip the solution
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| 94 | solution[idx] = !solution[idx];
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| 95 | var after = evalFunc(solution, null);
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| 96 | evaluations++;
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| 97 | if (IsBetter(maximization, after, quality)) {
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| 98 | steps++;
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| 99 | quality = after;
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| 100 | lastImp = i;
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| 101 | improved = true;
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| 102 | } else {
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| 103 | // undo the bitflip in case no improvement was made
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| 104 | solution[idx] = !solution[idx];
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| 105 | }
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| 106 | token.ThrowIfCancellationRequested();
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| 107 | }
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| 108 | } while (improved);
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| 109 |
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| 110 | return Tuple.Create(evaluations, steps);
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| 111 | }
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| 112 | }
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| 113 | }
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