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 MctsSampler {
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11 | private class TreeNode {
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12 | public string ident;
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13 | public int randomTries;
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14 | public IBanditPolicyActionInfo actionInfo;
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15 | public TreeNode[] children;
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16 | public bool done = false;
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17 |
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18 | public TreeNode(string id) {
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19 | this.ident = id;
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20 | }
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21 |
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22 | public override string ToString() {
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23 | return string.Format("Node({0} tries: {1}, done: {2}, policy: {3})", ident, actionInfo.Tries, done, actionInfo);
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24 | }
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25 | }
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26 |
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27 |
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28 | public event Action<string, double> FoundNewBestSolution;
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29 | public event Action<string, double> SolutionEvaluated;
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30 |
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31 | private readonly int maxLen;
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32 | private readonly IProblem problem;
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33 | private readonly Random random;
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34 | private readonly int randomTries;
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35 | private readonly IBanditPolicy policy;
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36 |
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37 | private List<TreeNode> updateChain;
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38 | private TreeNode rootNode;
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39 |
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40 | public int treeDepth;
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41 | public int treeSize;
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42 | private double bestQuality;
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43 |
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44 | public MctsSampler(IProblem problem, int maxLen, Random random, int randomTries, IBanditPolicy policy) {
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45 | this.maxLen = maxLen;
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46 | this.problem = problem;
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47 | this.random = random;
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48 | this.randomTries = randomTries;
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49 | this.policy = policy;
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50 | }
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51 |
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52 | public void Run(int maxIterations) {
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53 | bestQuality = double.MinValue;
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54 | InitPolicies(problem.Grammar);
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55 | for (int i = 0; !rootNode.done && i < maxIterations; i++) {
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56 | var sentence = SampleSentence(problem.Grammar).ToString();
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57 | var quality = problem.Evaluate(sentence) / problem.BestKnownQuality(maxLen);
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58 | Debug.Assert(quality >= 0 && quality <= 1.0);
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59 | DistributeReward(quality);
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60 |
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61 | RaiseSolutionEvaluated(sentence, quality);
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62 |
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63 | if (quality > bestQuality) {
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64 | bestQuality = quality;
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65 | RaiseFoundNewBestSolution(sentence, quality);
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66 | }
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67 | }
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68 |
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69 | // clean up
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70 | InitPolicies(problem.Grammar); GC.Collect();
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71 | }
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72 |
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73 | public void PrintStats() {
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74 | var n = rootNode;
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75 | Console.WriteLine("depth: {0,5} size: {1,10} root tries {2,10}, rootQ {3:F3}, bestQ {4:F3}", treeDepth, treeSize, n.actionInfo.Tries, n.actionInfo.Value, bestQuality);
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76 | while (n.children != null) {
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77 | Console.WriteLine();
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78 | Console.WriteLine("{0,5}->{1,-50}", n.ident, string.Join(" ", n.children.Select(ch => string.Format("{0,4}", ch.ident))));
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79 | Console.WriteLine("{0,5} {1,-50}", string.Empty, string.Join(" ", n.children.Select(ch => string.Format("{0,4:F2}", ch.actionInfo.Value * 10))));
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80 | Console.WriteLine("{0,5} {1,-50}", string.Empty, string.Join(" ", n.children.Select(ch => string.Format("{0,4}", ch.done ? "X" : ch.actionInfo.Tries.ToString()))));
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81 | //n.policy.PrintStats();
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82 | n = n.children.Where(ch => !ch.done).OrderByDescending(c => c.actionInfo.Value).First();
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83 | }
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84 | }
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85 |
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86 | private void InitPolicies(IGrammar grammar) {
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87 | this.updateChain = new List<TreeNode>();
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88 |
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89 | rootNode = new TreeNode(grammar.SentenceSymbol.ToString());
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90 | rootNode.actionInfo = policy.CreateActionInfo();
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91 | treeDepth = 0;
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92 | treeSize = 0;
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93 | }
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94 |
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95 | private Sequence SampleSentence(IGrammar grammar) {
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96 | updateChain.Clear();
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97 | var startPhrase = new Sequence(grammar.SentenceSymbol);
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98 | return CompleteSentence(grammar, startPhrase);
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99 | }
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100 |
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101 | private Sequence CompleteSentence(IGrammar g, Sequence phrase) {
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102 | if (phrase.Length > maxLen) throw new ArgumentException();
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103 | if (g.MinPhraseLength(phrase) > maxLen) throw new ArgumentException();
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104 | TreeNode n = rootNode;
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105 | var curDepth = 0;
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106 | while (!phrase.IsTerminal) {
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107 | updateChain.Add(n);
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108 |
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109 | if (n.randomTries < randomTries) {
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110 | n.randomTries++;
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111 | treeDepth = Math.Max(treeDepth, curDepth);
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112 | return g.CompleteSentenceRandomly(random, phrase, maxLen);
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113 | } else {
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114 | char nt = phrase.FirstNonTerminal;
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115 |
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116 | 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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117 | Debug.Assert(maxLenOfReplacement > 0);
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118 |
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119 | var alts = g.GetAlternatives(nt).Where(alt => g.MinPhraseLength(alt) <= maxLenOfReplacement);
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120 |
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121 | if (n.randomTries == randomTries && n.children == null) {
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122 | n.children = alts.Select(alt => new TreeNode(alt.ToString())).ToArray(); // create a new node for each alternative
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123 | foreach (var ch in n.children) ch.actionInfo = policy.CreateActionInfo();
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124 | treeSize += n.children.Length;
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125 | }
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126 | // => select using bandit policy
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127 | int selectedAltIdx = policy.SelectAction(random, n.children.Select(c => c.actionInfo));
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128 | Sequence selectedAlt = alts.ElementAt(selectedAltIdx);
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129 |
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130 | // replace nt with alt
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131 | phrase.ReplaceAt(phrase.FirstNonTerminalIndex, 1, selectedAlt);
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132 |
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133 | curDepth++;
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134 |
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135 | // prepare for next iteration
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136 | n = n.children[selectedAltIdx];
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137 | }
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138 | } // while
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139 |
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140 | updateChain.Add(n);
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141 |
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142 |
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143 | // the last node is a leaf node (sentence is done), so we never need to visit this node again
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144 | n.done = true;
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145 |
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146 | treeDepth = Math.Max(treeDepth, curDepth);
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147 | return phrase;
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148 | }
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149 |
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150 | private void DistributeReward(double reward) {
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151 | // iterate in reverse order (bottom up)
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152 | updateChain.Reverse();
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153 |
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154 | foreach (var e in updateChain) {
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155 | var node = e;
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156 | if (node.done) node.actionInfo.Disable();
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157 | if (node.children != null && node.children.All(c => c.done)) {
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158 | node.done = true;
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159 | node.actionInfo.Disable();
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160 | }
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161 | if (!node.done) {
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162 | node.actionInfo.UpdateReward(reward);
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163 | }
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164 | }
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165 | }
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166 |
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167 | private void RaiseSolutionEvaluated(string sentence, double quality) {
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168 | var handler = SolutionEvaluated;
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169 | if (handler != null) handler(sentence, quality);
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170 | }
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171 | private void RaiseFoundNewBestSolution(string sentence, double quality) {
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172 | var handler = FoundNewBestSolution;
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173 | if (handler != null) handler(sentence, quality);
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174 | }
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175 | }
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176 | }
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