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source: branches/GP-MoveOperators/HeuristicLab.Algorithms.ScatterSearch/3.3/ScatterSearch.cs @ 12336

Last change on this file since 12336 was 8630, checked in by jkarder, 12 years ago

#1331: added missing similarity calculators

File size: 22.5 KB
Line 
1#region License Information
2/* HeuristicLab
3 * Copyright (C) 2002-2012 Heuristic and Evolutionary Algorithms Laboratory (HEAL)
4 *
5 * This file is part of HeuristicLab.
6 *
7 * HeuristicLab is free software: you can redistribute it and/or modify
8 * it under the terms of the GNU General Public License as published by
9 * the Free Software Foundation, either version 3 of the License, or
10 * (at your option) any later version.
11 *
12 * HeuristicLab is distributed in the hope that it will be useful,
13 * but WITHOUT ANY WARRANTY; without even the implied warranty of
14 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
15 * GNU General Public License for more details.
16 *
17 * You should have received a copy of the GNU General Public License
18 * along with HeuristicLab. If not, see <http://www.gnu.org/licenses/>.
19 */
20#endregion
21
22using System;
23using System.Linq;
24using HeuristicLab.Analysis;
25using HeuristicLab.Common;
26using HeuristicLab.Core;
27using HeuristicLab.Data;
28using HeuristicLab.Operators;
29using HeuristicLab.Optimization;
30using HeuristicLab.Optimization.Operators;
31using HeuristicLab.Parameters;
32using HeuristicLab.Persistence.Default.CompositeSerializers.Storable;
33using HeuristicLab.Random;
34using HeuristicLab.Selection;
35
36namespace HeuristicLab.Algorithms.ScatterSearch {
37  /// <summary>
38  /// A scatter search algorithm.
39  /// </summary>
40  [Item("Scatter Search", "A scatter search algorithm.")]
41  [Creatable("Algorithms")]
42  [StorableClass]
43  public sealed class ScatterSearch : HeuristicOptimizationEngineAlgorithm, IStorableContent {
44    public string Filename { get; set; }
45
46    #region Problem Properties
47    public override Type ProblemType {
48      get { return typeof(ISingleObjectiveHeuristicOptimizationProblem); }
49    }
50    public new ISingleObjectiveHeuristicOptimizationProblem Problem {
51      get { return (ISingleObjectiveHeuristicOptimizationProblem)base.Problem; }
52      set { base.Problem = value; }
53    }
54    #endregion
55
56    #region Parameter Properties
57    public IValueParameter<MultiAnalyzer> AnalyzerParameter {
58      get { return (IValueParameter<MultiAnalyzer>)Parameters["Analyzer"]; }
59    }
60    public IConstrainedValueParameter<ICrossover> CrossoverParameter {
61      get { return (IConstrainedValueParameter<ICrossover>)Parameters["Crossover"]; }
62    }
63    public IValueParameter<BoolValue> ExecutePathRelinkingParameter {
64      get { return (IValueLookupParameter<BoolValue>)Parameters["ExecutePathRelinking"]; }
65    }
66    public IConstrainedValueParameter<IImprovementOperator> ImproverParameter {
67      get { return (IConstrainedValueParameter<IImprovementOperator>)Parameters["Improver"]; }
68    }
69    public IValueParameter<IntValue> MaximumIterationsParameter {
70      get { return (IValueParameter<IntValue>)Parameters["MaximumIterations"]; }
71    }
72    public IValueParameter<IntValue> NumberOfHighQualitySolutionsParameter {
73      get { return (IValueParameter<IntValue>)Parameters["NumberOfHighQualitySolutions"]; }
74    }
75    public IConstrainedValueParameter<IPathRelinker> PathRelinkerParameter {
76      get { return (IConstrainedValueParameter<IPathRelinker>)Parameters["PathRelinker"]; }
77    }
78    public IValueParameter<IntValue> PopulationSizeParameter {
79      get { return (IValueParameter<IntValue>)Parameters["PopulationSize"]; }
80    }
81    public IValueParameter<IntValue> ReferenceSetSizeParameter {
82      get { return (IValueParameter<IntValue>)Parameters["ReferenceSetSize"]; }
83    }
84    public IValueParameter<IntValue> SeedParameter {
85      get { return (IValueParameter<IntValue>)Parameters["Seed"]; }
86    }
87    public IValueParameter<BoolValue> SetSeedRandomlyParameter {
88      get { return (IValueParameter<BoolValue>)Parameters["SetSeedRandomly"]; }
89    }
90    public IConstrainedValueParameter<ISingleObjectiveSolutionSimilarityCalculator> SimilarityCalculatorParameter {
91      get { return (IConstrainedValueParameter<ISingleObjectiveSolutionSimilarityCalculator>)Parameters["SimilarityCalculator"]; }
92    }
93    #endregion
94
95    #region Properties
96    public MultiAnalyzer Analyzer {
97      get { return AnalyzerParameter.Value; }
98      set { AnalyzerParameter.Value = value; }
99    }
100    public ICrossover Crossover {
101      get { return CrossoverParameter.Value; }
102      set { CrossoverParameter.Value = value; }
103    }
104    public BoolValue ExecutePathRelinking {
105      get { return ExecutePathRelinkingParameter.Value; }
106      set { ExecutePathRelinkingParameter.Value = value; }
107    }
108    public IImprovementOperator Improver {
109      get { return ImproverParameter.Value; }
110      set { ImproverParameter.Value = value; }
111    }
112    public IntValue MaximumIterations {
113      get { return MaximumIterationsParameter.Value; }
114      set { MaximumIterationsParameter.Value = value; }
115    }
116    public IntValue NumberOfHighQualitySolutions {
117      get { return NumberOfHighQualitySolutionsParameter.Value; }
118      set { NumberOfHighQualitySolutionsParameter.Value = value; }
119    }
120    public IPathRelinker PathRelinker {
121      get { return PathRelinkerParameter.Value; }
122      set { PathRelinkerParameter.Value = value; }
123    }
124    public IntValue PopulationSize {
125      get { return PopulationSizeParameter.Value; }
126      set { PopulationSizeParameter.Value = value; }
127    }
128    public IntValue ReferenceSetSize {
129      get { return ReferenceSetSizeParameter.Value; }
130      set { ReferenceSetSizeParameter.Value = value; }
131    }
132    public IntValue Seed {
133      get { return SeedParameter.Value; }
134      set { SeedParameter.Value = value; }
135    }
136    public BoolValue SetSeedRandomly {
137      get { return SetSeedRandomlyParameter.Value; }
138      set { SetSeedRandomlyParameter.Value = value; }
139    }
140    public ISingleObjectiveSolutionSimilarityCalculator SimilarityCalculator {
141      get { return SimilarityCalculatorParameter.Value; }
142      set { SimilarityCalculatorParameter.Value = value; }
143    }
144    private RandomCreator RandomCreator {
145      get { return (RandomCreator)OperatorGraph.InitialOperator; }
146    }
147    private SolutionsCreator SolutionsCreator {
148      get { return (SolutionsCreator)RandomCreator.Successor; }
149    }
150    private ScatterSearchMainLoop MainLoop {
151      get { return FindMainLoop(SolutionsCreator.Successor); }
152    }
153
154    [Storable]
155    private BestAverageWorstQualityAnalyzer qualityAnalyzer;
156    #endregion
157
158    [StorableConstructor]
159    private ScatterSearch(bool deserializing) : base(deserializing) { }
160    [StorableHook(HookType.AfterDeserialization)]
161    private void AfterDeserialization() {
162      Initialize();
163    }
164    private ScatterSearch(ScatterSearch original, Cloner cloner)
165      : base(original, cloner) {
166      qualityAnalyzer = cloner.Clone(original.qualityAnalyzer);
167      Initialize();
168    }
169    public override IDeepCloneable Clone(Cloner cloner) {
170      return new ScatterSearch(this, cloner);
171    }
172    public ScatterSearch()
173      : base() {
174      #region Create parameters
175      Parameters.Add(new ValueParameter<MultiAnalyzer>("Analyzer", "The analyzer used to analyze each iteration.", new MultiAnalyzer()));
176      Parameters.Add(new ConstrainedValueParameter<ICrossover>("Crossover", "The operator used to cross solutions."));
177      Parameters.Add(new ValueParameter<BoolValue>("ExecutePathRelinking", "True if path relinking should be executed instead of crossover, otherwise false.", new BoolValue(true)));
178      Parameters.Add(new ConstrainedValueParameter<IImprovementOperator>("Improver", "The operator used to improve solutions."));
179      Parameters.Add(new ValueParameter<IntValue>("MaximumIterations", "The maximum number of iterations which should be processed.", new IntValue(100)));
180      Parameters.Add(new ValueParameter<IntValue>("NumberOfHighQualitySolutions", "The number of high quality solutions in the reference set.", new IntValue(5)));
181      Parameters.Add(new ConstrainedValueParameter<IPathRelinker>("PathRelinker", "The operator used to execute path relinking."));
182      Parameters.Add(new ValueParameter<IntValue>("PopulationSize", "The size of the population of solutions.", new IntValue(50)));
183      Parameters.Add(new ValueParameter<IntValue>("ReferenceSetSize", "The size of the reference set.", new IntValue(20)));
184      Parameters.Add(new ValueParameter<IntValue>("Seed", "The random seed used to initialize the new pseudo random number generator.", new IntValue(0)));
185      Parameters.Add(new ValueParameter<BoolValue>("SetSeedRandomly", "True if the random seed should be set to a random value, otherwise false.", new BoolValue(true)));
186      Parameters.Add(new ConstrainedValueParameter<ISingleObjectiveSolutionSimilarityCalculator>("SimilarityCalculator", "The operator used to calculate the similarity between two solutions."));
187      #endregion
188
189      #region Create operators
190      RandomCreator randomCreator = new RandomCreator();
191      SolutionsCreator solutionsCreator = new SolutionsCreator();
192      UniformSubScopesProcessor uniformSubScopesProcessor = new UniformSubScopesProcessor();
193      Placeholder solutionEvaluator = new Placeholder();
194      Placeholder solutionImprover = new Placeholder();
195      VariableCreator variableCreator = new VariableCreator();
196      DataReducer dataReducer = new DataReducer();
197      ResultsCollector resultsCollector = new ResultsCollector();
198      BestSelector bestSelector = new BestSelector();
199      ScatterSearchMainLoop mainLoop = new ScatterSearchMainLoop();
200      #endregion
201
202      #region Create operator graph
203      OperatorGraph.InitialOperator = randomCreator;
204      randomCreator.RandomParameter.ActualName = "Random";
205      randomCreator.SeedParameter.ActualName = SeedParameter.Name;
206      randomCreator.SetSeedRandomlyParameter.ActualName = SetSeedRandomlyParameter.Name;
207      randomCreator.Successor = solutionsCreator;
208
209      solutionsCreator.Name = "DiversificationGenerationMethod";
210      solutionsCreator.NumberOfSolutionsParameter.ActualName = "PopulationSize";
211      solutionsCreator.Successor = uniformSubScopesProcessor;
212
213      uniformSubScopesProcessor.Operator = solutionImprover;
214      uniformSubScopesProcessor.ParallelParameter.Value = new BoolValue(true);
215      uniformSubScopesProcessor.Successor = variableCreator;
216
217      solutionImprover.Name = "SolutionImprover";
218      solutionImprover.OperatorParameter.ActualName = "Improver";
219      solutionImprover.Successor = solutionEvaluator;
220
221      solutionEvaluator.Name = "SolutionEvaluator";
222      solutionEvaluator.OperatorParameter.ActualName = "Evaluator";
223      solutionEvaluator.Successor = null;
224
225      variableCreator.Name = "Initialize EvaluatedSolutions";
226      variableCreator.CollectedValues.Add(new ValueParameter<IntValue>("EvaluatedSolutions", new IntValue()));
227      variableCreator.Successor = dataReducer;
228
229      dataReducer.Name = "Increment EvaluatedSolutions";
230      dataReducer.ParameterToReduce.ActualName = "LocalEvaluatedSolutions";
231      dataReducer.TargetParameter.ActualName = "EvaluatedSolutions";
232      dataReducer.ReductionOperation.Value = new ReductionOperation(ReductionOperations.Sum);
233      dataReducer.TargetOperation.Value = new ReductionOperation(ReductionOperations.Sum);
234      dataReducer.Successor = resultsCollector;
235
236      resultsCollector.Name = "ResultsCollector";
237      resultsCollector.CollectedValues.Add(new LookupParameter<IntValue>("EvaluatedSolutions", null, "EvaluatedSolutions"));
238      resultsCollector.Successor = bestSelector;
239
240      bestSelector.NumberOfSelectedSubScopesParameter.ActualName = NumberOfHighQualitySolutionsParameter.Name;
241      bestSelector.CopySelected = new BoolValue(false);
242      bestSelector.Successor = mainLoop;
243
244      mainLoop.MaximumIterationsParameter.ActualName = MaximumIterationsParameter.Name;
245      mainLoop.RandomParameter.ActualName = randomCreator.RandomParameter.ActualName;
246      mainLoop.ResultsParameter.ActualName = "Results";
247      mainLoop.AnalyzerParameter.ActualName = AnalyzerParameter.Name;
248      mainLoop.IterationsParameter.ActualName = "Iterations";
249      mainLoop.EvaluatedSolutionsParameter.ActualName = "EvaluatedSolutions";
250      mainLoop.CrossoverParameter.ActualName = CrossoverParameter.Name;
251      mainLoop.PopulationSizeParameter.ActualName = PopulationSizeParameter.Name;
252      mainLoop.NumberOfHighQualitySolutionsParameter.ActualName = NumberOfHighQualitySolutionsParameter.Name;
253      mainLoop.Successor = null;
254      #endregion
255
256      qualityAnalyzer = new BestAverageWorstQualityAnalyzer();
257      ParameterizeAnalyzers();
258      UpdateAnalyzers();
259
260      Initialize();
261    }
262
263    public override void Prepare() {
264      if (Problem != null && Improver != null && PathRelinker != null && SimilarityCalculator != null)
265        base.Prepare();
266    }
267
268    #region Events
269    protected override void OnProblemChanged() {
270      ParameterizeStochasticOperator(Problem.SolutionCreator);
271      ParameterizeStochasticOperator(Problem.Evaluator);
272      foreach (IOperator op in Problem.Operators.OfType<IOperator>()) ParameterizeStochasticOperator(op);
273      ParameterizeAnalyzers();
274      ParameterizeSolutionsCreator();
275      ParameterizeBestSelector();
276      UpdateAnalyzers();
277      UpdateCrossovers();
278      UpdateImprovers();
279      UpdatePathRelinkers();
280      UpdateSimilarityCalculators();
281      ParameterizeMainLoop();
282      Problem.Evaluator.QualityParameter.ActualNameChanged += new EventHandler(Evaluator_QualityParameter_ActualNameChanged);
283      base.OnProblemChanged();
284    }
285    protected override void Problem_SolutionCreatorChanged(object sender, EventArgs e) {
286      ParameterizeStochasticOperator(Problem.SolutionCreator);
287      ParameterizeSolutionsCreator();
288      base.Problem_SolutionCreatorChanged(sender, e);
289    }
290    protected override void Problem_EvaluatorChanged(object sender, EventArgs e) {
291      ParameterizeStochasticOperator(Problem.Evaluator);
292      ParameterizeSolutionsCreator();
293      ParameterizeMainLoop();
294      ParameterizeAnalyzers();
295      Problem.Evaluator.QualityParameter.ActualNameChanged += new EventHandler(Evaluator_QualityParameter_ActualNameChanged);
296      base.Problem_EvaluatorChanged(sender, e);
297    }
298    protected override void Problem_OperatorsChanged(object sender, EventArgs e) {
299      foreach (IOperator op in Problem.Operators.OfType<IOperator>()) ParameterizeStochasticOperator(op);
300      UpdateAnalyzers();
301      UpdateCrossovers();
302      UpdatePathRelinkers();
303      UpdateSimilarityCalculators();
304      UpdateImprovers();
305      ParameterizeMainLoop();
306      ParameterizeAnalyzers();
307      base.Problem_OperatorsChanged(sender, e);
308    }
309    private void SimilarityCalculatorParameter_ValueChanged(object sender, EventArgs e) {
310      ParameterizeMainLoop();
311    }
312    private void Evaluator_QualityParameter_ActualNameChanged(object sender, EventArgs e) {
313      ParameterizeMainLoop();
314      ParameterizeAnalyzers();
315      ParameterizeBestSelector();
316      ParameterizeSimilarityCalculators();
317    }
318    #endregion
319
320    #region Helpers
321    private void Initialize() {
322      SimilarityCalculatorParameter.ValueChanged += new EventHandler(SimilarityCalculatorParameter_ValueChanged);
323      if (Problem != null)
324        Problem.Evaluator.QualityParameter.ActualNameChanged += new EventHandler(Evaluator_QualityParameter_ActualNameChanged);
325    }
326    private void UpdateAnalyzers() {
327      Analyzer.Operators.Clear();
328      if (Problem != null) {
329        foreach (IAnalyzer analyzer in Problem.Operators.OfType<IAnalyzer>()) {
330          foreach (IScopeTreeLookupParameter param in analyzer.Parameters.OfType<IScopeTreeLookupParameter>())
331            param.Depth = 1;
332          Analyzer.Operators.Add(analyzer, analyzer.EnabledByDefault);
333        }
334      }
335      Analyzer.Operators.Add(qualityAnalyzer, qualityAnalyzer.EnabledByDefault);
336    }
337    private void UpdateCrossovers() {
338      ICrossover oldCrossover = CrossoverParameter.Value;
339      CrossoverParameter.ValidValues.Clear();
340      ICrossover defaultCrossover = Problem.Operators.OfType<ICrossover>().FirstOrDefault();
341
342      foreach (ICrossover crossover in Problem.Operators.OfType<ICrossover>().OrderBy(x => x.Name))
343        CrossoverParameter.ValidValues.Add(crossover);
344
345      if (oldCrossover != null) {
346        ICrossover crossover = CrossoverParameter.ValidValues.FirstOrDefault(x => x.GetType() == oldCrossover.GetType());
347        if (crossover != null) CrossoverParameter.Value = crossover;
348        else oldCrossover = null;
349      }
350      if (oldCrossover == null && defaultCrossover != null)
351        CrossoverParameter.Value = defaultCrossover;
352    }
353    private void UpdateImprovers() {
354      IImprovementOperator oldImprover = ImproverParameter.Value;
355      ImproverParameter.ValidValues.Clear();
356      IImprovementOperator defaultImprover = Problem.Operators.OfType<IImprovementOperator>().FirstOrDefault();
357
358      foreach (IImprovementOperator improver in Problem.Operators.OfType<IImprovementOperator>().OrderBy(x => x.Name))
359        ImproverParameter.ValidValues.Add(improver);
360
361      if (oldImprover != null) {
362        IImprovementOperator improver = ImproverParameter.ValidValues.FirstOrDefault(x => x.GetType() == oldImprover.GetType());
363        if (improver != null) ImproverParameter.Value = improver;
364        else oldImprover = null;
365      }
366      if (oldImprover == null && defaultImprover != null)
367        ImproverParameter.Value = defaultImprover;
368    }
369    private void UpdatePathRelinkers() {
370      IPathRelinker oldPathRelinker = PathRelinkerParameter.Value;
371      PathRelinkerParameter.ValidValues.Clear();
372      IPathRelinker defaultPathRelinker = Problem.Operators.OfType<IPathRelinker>().FirstOrDefault();
373
374      foreach (IPathRelinker pathRelinker in Problem.Operators.OfType<IPathRelinker>().OrderBy(x => x.Name))
375        PathRelinkerParameter.ValidValues.Add(pathRelinker);
376
377      if (oldPathRelinker != null) {
378        IPathRelinker pathRelinker = PathRelinkerParameter.ValidValues.FirstOrDefault(x => x.GetType() == oldPathRelinker.GetType());
379        if (pathRelinker != null) PathRelinkerParameter.Value = pathRelinker;
380        else oldPathRelinker = null;
381      }
382      if (oldPathRelinker == null && defaultPathRelinker != null)
383        PathRelinkerParameter.Value = defaultPathRelinker;
384    }
385    private void UpdateSimilarityCalculators() {
386      ISingleObjectiveSolutionSimilarityCalculator oldSimilarityCalculator = SimilarityCalculatorParameter.Value;
387      SimilarityCalculatorParameter.ValidValues.Clear();
388      ISingleObjectiveSolutionSimilarityCalculator defaultSimilarityCalculator = Problem.Operators.OfType<ISingleObjectiveSolutionSimilarityCalculator>().FirstOrDefault();
389
390      SimilarityCalculatorParameter.ValidValues.Add(new QualitySimilarityCalculator { QualityVariableName = Problem.Evaluator.QualityParameter.ActualName });
391      SimilarityCalculatorParameter.ValidValues.Add(new NoSimilarityCalculator());
392
393      foreach (ISingleObjectiveSolutionSimilarityCalculator similarityCalculator in Problem.Operators.OfType<ISingleObjectiveSolutionSimilarityCalculator>())
394        SimilarityCalculatorParameter.ValidValues.Add(similarityCalculator);
395
396      if (oldSimilarityCalculator != null) {
397        ISingleObjectiveSolutionSimilarityCalculator similarityCalculator = SimilarityCalculatorParameter.ValidValues.FirstOrDefault(x => x.GetType() == oldSimilarityCalculator.GetType());
398        if (similarityCalculator != null) SimilarityCalculatorParameter.Value = similarityCalculator;
399        else oldSimilarityCalculator = null;
400      }
401      if (oldSimilarityCalculator == null && defaultSimilarityCalculator != null)
402        SimilarityCalculatorParameter.Value = defaultSimilarityCalculator;
403    }
404    private void ParameterizeBestSelector() {
405      OperatorGraph.Operators.OfType<ISingleObjectiveSelector>()
406                             .First().QualityParameter.ActualName = Problem.Evaluator.QualityParameter.ActualName;
407    }
408    private void ParameterizeSolutionsCreator() {
409      SolutionsCreator.EvaluatorParameter.ActualName = Problem.EvaluatorParameter.Name;
410      SolutionsCreator.SolutionCreatorParameter.ActualName = Problem.SolutionCreatorParameter.Name;
411    }
412    private void ParameterizeMainLoop() {
413      if (Problem != null && Improver != null) {
414        MainLoop.BestKnownQualityParameter.ActualName = Problem.BestKnownQualityParameter.Name;
415        MainLoop.MaximizationParameter.ActualName = Problem.MaximizationParameter.Name;
416        MainLoop.QualityParameter.ActualName = Problem.Evaluator.QualityParameter.ActualName;
417        MainLoop.OperatorGraph.Operators.OfType<PopulationRebuildMethod>().Single().QualityParameter.ActualName = Problem.Evaluator.QualityParameter.ActualName;
418        MainLoop.OperatorGraph.Operators.OfType<SolutionPoolUpdateMethod>().Single().QualityParameter.ActualName = Problem.Evaluator.QualityParameter.ActualName;
419        foreach (ISimilarityBasedOperator op in MainLoop.OperatorGraph.Operators.OfType<ISimilarityBasedOperator>())
420          op.SimilarityCalculator = SimilarityCalculator;
421      }
422    }
423    private void ParameterizeStochasticOperator(IOperator op) {
424      if (op is IStochasticOperator) {
425        IStochasticOperator stOp = (IStochasticOperator)op;
426        stOp.RandomParameter.ActualName = RandomCreator.RandomParameter.ActualName;
427        stOp.RandomParameter.Hidden = true;
428      }
429    }
430    private void ParameterizeAnalyzers() {
431      qualityAnalyzer.ResultsParameter.ActualName = "Results";
432      qualityAnalyzer.ResultsParameter.Hidden = true;
433      if (Problem != null) {
434        qualityAnalyzer.MaximizationParameter.ActualName = Problem.MaximizationParameter.Name;
435        qualityAnalyzer.MaximizationParameter.Hidden = true;
436        qualityAnalyzer.QualityParameter.Hidden = false;
437        qualityAnalyzer.BestKnownQualityParameter.ActualName = Problem.BestKnownQualityParameter.Name;
438        qualityAnalyzer.BestKnownQualityParameter.Hidden = true;
439      } else {
440        qualityAnalyzer.MaximizationParameter.Hidden = false;
441        qualityAnalyzer.BestKnownQualityParameter.Hidden = false;
442      }
443    }
444    private void ParameterizeSimilarityCalculators() {
445      foreach (ISingleObjectiveSolutionSimilarityCalculator calc in SimilarityCalculatorParameter.ValidValues) {
446        calc.QualityVariableName = Problem.Evaluator.QualityParameter.ActualName;
447      }
448    }
449    private ScatterSearchMainLoop FindMainLoop(IOperator start) {
450      IOperator mainLoop = start;
451      while (mainLoop != null && !(mainLoop is ScatterSearchMainLoop))
452        mainLoop = ((SingleSuccessorOperator)mainLoop).Successor;
453      return mainLoop as ScatterSearchMainLoop;
454    }
455    #endregion
456  }
457}
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