1 | using System;
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2 | using System.Collections.Generic;
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3 | using System.Diagnostics;
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4 | using System.Linq;
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5 | using System.Text;
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6 | using HeuristicLab.Algorithms.Bandits;
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7 | using HeuristicLab.Problems.GrammaticalOptimization;
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8 |
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9 | namespace HeuristicLab.Algorithms.GrammaticalOptimization {
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10 | public class MctsContextualSampler {
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11 | private class TreeNode {
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12 | public int randomTries;
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13 | public int policyTries;
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14 | public TreeNode[] children;
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15 | public readonly ReadonlySequence phrase;
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16 | public readonly ReadonlySequence alt;
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17 |
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18 | // phrase represents the phrase of the state and alt represents how the phrase has been reached from the parent state
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19 | public TreeNode(ReadonlySequence phrase, ReadonlySequence alt) {
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20 | this.phrase = phrase;
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21 | this.alt = alt;
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22 | }
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23 |
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24 | public override string ToString() {
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25 | return string.Format("Node({0} tries: {1})", phrase, randomTries + policyTries);
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26 | }
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27 | }
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28 |
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29 |
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30 | public event Action<string, double> FoundNewBestSolution;
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31 | public event Action<string, double> SolutionEvaluated;
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32 |
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33 | private readonly int maxLen;
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34 | private readonly IProblem problem;
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35 | private readonly Random random;
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36 | private readonly int randomTries;
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37 | private readonly IGrammarPolicy policy;
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38 |
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39 | private List<Tuple<ReadonlySequence, ReadonlySequence, ReadonlySequence>> updateChain;
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40 | private TreeNode rootNode;
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41 |
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42 | public int treeDepth;
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43 | public int treeSize;
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44 |
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45 | // public MctsSampler(IProblem problem, int maxLen, Random random) :
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46 | // this(problem, maxLen, random, 10, (rand, numActions) => new EpsGreedyPolicy(rand, numActions, 0.1)) {
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47 | //
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48 | // }
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49 |
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50 | public MctsContextualSampler(IProblem problem, int maxLen, Random random, int randomTries, IGrammarPolicy policy) {
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51 | this.maxLen = maxLen;
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52 | this.problem = problem;
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53 | this.random = random;
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54 | this.randomTries = randomTries;
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55 | this.policy = policy;
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56 | }
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57 |
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58 | public void Run(int maxIterations) {
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59 | double bestQuality = double.MinValue;
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60 | InitPolicies(problem.Grammar);
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61 | for (int i = 0; !policy.Done(rootNode.phrase) && i < maxIterations; i++) {
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62 | var sentence = SampleSentence(problem.Grammar).ToString();
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63 | var quality = problem.Evaluate(sentence) / problem.BestKnownQuality(maxLen);
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64 | Debug.Assert(quality >= 0 && quality <= 1.0);
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65 | DistributeReward(quality);
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66 |
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67 | RaiseSolutionEvaluated(sentence, quality);
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68 |
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69 | if (quality > bestQuality) {
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70 | bestQuality = quality;
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71 | RaiseFoundNewBestSolution(sentence, quality);
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72 | }
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73 | }
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74 |
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75 | // clean up
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76 | InitPolicies(problem.Grammar); GC.Collect();
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77 | }
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78 |
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79 | public void PrintStats() {
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80 | var n = rootNode;
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81 | Console.WriteLine("depth: {0,5} size: {1,10} root tries {2,10}", treeDepth, treeSize, rootNode.policyTries + rootNode.randomTries);
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82 | while (n.children != null) {
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83 | Console.WriteLine();
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84 | Console.WriteLine("{0,5}->{1,-50}", n.alt, string.Join(" ", n.children.Select(ch => string.Format("{0,4}", ch.alt))));
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85 | Console.WriteLine("{0,5} {1,-50}", string.Empty, string.Join(" ", n.children.Select(ch => string.Format("{0,4}", ch.randomTries + ch.policyTries))));
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86 | //n.policy.PrintStats();
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87 | n = n.children.OrderByDescending(c => c.policyTries).First();
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88 | }
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89 | Console.ReadLine();
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90 | }
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91 |
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92 | private void InitPolicies(IGrammar grammar) {
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93 | this.updateChain = new List<Tuple<ReadonlySequence, ReadonlySequence, ReadonlySequence>>();
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94 |
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95 | rootNode = new TreeNode(new ReadonlySequence(grammar.SentenceSymbol), new ReadonlySequence("$"));
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96 | treeDepth = 0;
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97 | treeSize = 0;
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98 | }
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99 |
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100 | private Sequence SampleSentence(IGrammar grammar) {
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101 | updateChain.Clear();
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102 | var startPhrase = new Sequence(rootNode.phrase);
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103 | return CompleteSentence(grammar, startPhrase);
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104 | }
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105 |
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106 | private Sequence CompleteSentence(IGrammar g, Sequence phrase) {
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107 | if (phrase.Length > maxLen) throw new ArgumentException();
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108 | if (g.MinPhraseLength(phrase) > maxLen) throw new ArgumentException();
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109 | TreeNode parent = null;
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110 | TreeNode n = rootNode;
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111 | bool done = false;
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112 | var curDepth = 0;
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113 | while (!done) {
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114 | if (parent != null)
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115 | updateChain.Add(Tuple.Create(parent.phrase, n.alt, n.phrase));
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116 |
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117 | if (n.randomTries < randomTries) {
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118 | n.randomTries++;
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119 | treeDepth = Math.Max(treeDepth, curDepth);
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120 | return g.CompleteSentenceRandomly(random, phrase, maxLen);
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121 | } else {
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122 | char nt = phrase.FirstNonTerminal;
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123 |
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124 | int maxLenOfReplacement = maxLen - (phrase.Length - 1); // replacing aAb with maxLen 4 means we can only use alternatives with a minPhraseLen <= 2
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125 | Debug.Assert(maxLenOfReplacement > 0);
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126 |
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127 | var alts = g.GetAlternatives(nt).Where(alt => g.MinPhraseLength(alt) <= maxLenOfReplacement);
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128 |
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129 | if (n.randomTries == randomTries && n.children == null) {
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130 | n.children = new TreeNode[alts.Count()];
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131 | int cIdx = 0;
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132 | foreach (var alt in alts) {
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133 | var newPhrase = new Sequence(phrase);
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134 | newPhrase.ReplaceAt(phrase.FirstNonTerminalIndex, 1, alt);
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135 | n.children[cIdx++] = new TreeNode(new ReadonlySequence(newPhrase), new ReadonlySequence(alt));
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136 | }
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137 | treeSize += n.children.Length;
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138 | }
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139 |
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140 | n.policyTries++;
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141 | // => select using bandit policy
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142 | ReadonlySequence selectedAlt = policy.SelectAction(random, n.phrase, n.children.Select(c => c.alt));
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143 |
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144 | // replace nt with alt
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145 | phrase.ReplaceAt(phrase.FirstNonTerminalIndex, 1, selectedAlt);
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146 |
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147 | curDepth++;
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148 |
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149 | done = phrase.IsTerminal;
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150 |
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151 | // prepare for next iteration
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152 | parent = n;
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153 | n = n.children.Single(ch => ch.alt == selectedAlt); // TODO: perf
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154 | }
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155 | } // while
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156 |
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157 | n.policyTries++;
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158 | updateChain.Add(Tuple.Create(parent.phrase, n.alt, n.phrase));
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159 |
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160 |
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161 | treeDepth = Math.Max(treeDepth, curDepth);
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162 | return phrase;
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163 | }
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164 |
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165 | private void DistributeReward(double reward) {
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166 | // iterate in reverse order (bottom up)
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167 | updateChain.Reverse();
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168 |
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169 | foreach (var e in updateChain) {
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170 | var state = e.Item1;
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171 | var action = e.Item2;
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172 | var newState = e.Item3;
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173 | policy.UpdateReward(state, action, reward, newState);
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174 | //policy.UpdateReward(action, reward / updateChain.Count);
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175 | }
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176 | }
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177 |
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178 | private void RaiseSolutionEvaluated(string sentence, double quality) {
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179 | var handler = SolutionEvaluated;
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180 | if (handler != null) handler(sentence, quality);
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181 | }
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182 | private void RaiseFoundNewBestSolution(string sentence, double quality) {
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183 | var handler = FoundNewBestSolution;
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184 | if (handler != null) handler(sentence, quality);
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185 | }
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186 | }
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187 | }
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