[11744] | 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.Common;
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| 8 | using HeuristicLab.Problems.GrammaticalOptimization;
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| 9 |
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| 10 | namespace HeuristicLab.Algorithms.GrammaticalOptimization {
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| 11 | // SARSA (fig. 6.9 in Sutton & Barto)
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| 12 | public class TemporalDifferenceTreeSearchSampler {
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| 13 | private class TreeNode {
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| 14 | public string ident;
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| 15 | public int randomTries;
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| 16 | public double q;
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| 17 | public int tries;
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| 18 | public TreeNode[] children;
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| 19 | public bool done = false;
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| 20 |
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| 21 | public TreeNode(string id) {
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| 22 | this.ident = id;
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| 23 | }
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| 24 |
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| 25 | public override string ToString() {
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| 26 | return string.Format("Node({0} tries: {1}, done: {2})", ident, tries, done);
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| 27 | }
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| 28 | }
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| 29 |
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| 30 |
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| 31 | public event Action<string, double> FoundNewBestSolution;
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| 32 | public event Action<string, double> SolutionEvaluated;
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| 33 |
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| 34 | private readonly int maxLen;
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| 35 | private readonly IProblem problem;
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| 36 | private readonly Random random;
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| 37 | private readonly int randomTries;
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| 38 | private readonly IBanditPolicy policy;
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| 39 |
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| 40 | private List<TreeNode> updateChain;
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| 41 | private TreeNode rootNode;
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| 42 |
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| 43 | public int treeDepth;
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| 44 | public int treeSize;
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| 45 | private double bestQuality;
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| 46 |
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| 47 |
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| 48 | public TemporalDifferenceTreeSearchSampler(IProblem problem, int maxLen, Random random, int randomTries, IBanditPolicy policy) {
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| 49 | this.maxLen = maxLen;
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| 50 | this.problem = problem;
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| 51 | this.random = random;
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| 52 | this.randomTries = randomTries;
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| 53 | this.policy = policy;
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| 54 | }
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| 55 |
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| 56 | public void Run(int maxIterations) {
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| 57 | InitPolicies(problem.Grammar);
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| 58 | for (int i = 0; !rootNode.done && i < maxIterations; i++) {
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| 59 | var sentence = SampleSentence(problem.Grammar).ToString();
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| 60 | var quality = problem.Evaluate(sentence) / problem.BestKnownQuality(maxLen);
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| 61 | Debug.Assert(quality >= 0 && quality <= 1.0);
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| 62 | DistributeReward(quality);
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| 63 |
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| 64 | RaiseSolutionEvaluated(sentence, quality);
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| 65 |
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| 66 | if (quality > bestQuality) {
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| 67 | bestQuality = quality;
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| 68 | RaiseFoundNewBestSolution(sentence, quality);
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| 69 | }
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| 70 | }
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| 71 |
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| 72 | // clean up
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| 73 | InitPolicies(problem.Grammar); GC.Collect();
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| 74 | }
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| 75 |
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| 76 | public void PrintStats() {
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| 77 | var n = rootNode;
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| 78 | Console.WriteLine("depth: {0,5} size: {1,10} root tries {2,10}, rootQ {3:F3}, bestQ {4:F3}", treeDepth, treeSize, n.tries, n.q, bestQuality);
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| 79 | while (n.children != null) {
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| 80 | Console.WriteLine();
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| 81 | Console.WriteLine("{0,5}->{1,-50}", n.ident, string.Join(" ", n.children.Select(ch => string.Format("{0,4}", ch.ident))));
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| 82 | Console.WriteLine("{0,5} {1,-50}", string.Empty, string.Join(" ", n.children.Select(ch => string.Format("{0,4:F2}", ch.q * 10))));
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| 83 | Console.WriteLine("{0,5} {1,-50}", string.Empty, string.Join(" ", n.children.Select(ch => string.Format("{0,4}", ch.done ? "X" : ch.tries.ToString()))));
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| 84 | //n.policy.PrintStats();
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| 85 | n = n.children.Where(ch => !ch.done).OrderByDescending(c => c.q).First();
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| 86 | }
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| 87 | //Console.ReadLine();
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| 88 | }
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| 89 |
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| 90 | private void InitPolicies(IGrammar grammar) {
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| 91 | this.updateChain = new List<TreeNode>();
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| 92 |
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| 93 | rootNode = new TreeNode(grammar.SentenceSymbol.ToString());
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| 94 | treeDepth = 0;
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| 95 | treeSize = 0;
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| 96 | }
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| 97 |
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| 98 | private Sequence SampleSentence(IGrammar grammar) {
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| 99 | updateChain.Clear();
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| 100 | var startPhrase = new Sequence(grammar.SentenceSymbol);
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| 101 | return CompleteSentence(grammar, startPhrase);
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| 102 | }
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| 103 |
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| 104 | private Sequence CompleteSentence(IGrammar g, Sequence phrase) {
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| 105 | if (phrase.Length > maxLen) throw new ArgumentException();
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| 106 | if (g.MinPhraseLength(phrase) > maxLen) throw new ArgumentException();
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| 107 | TreeNode n = rootNode;
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| 108 | var curDepth = 0;
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| 109 | while (!phrase.IsTerminal) {
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| 110 | updateChain.Add(n);
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| 111 |
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| 112 | if (n.randomTries < randomTries) {
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| 113 | n.randomTries++;
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| 114 | treeDepth = Math.Max(treeDepth, curDepth);
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| 115 | return g.CompleteSentenceRandomly(random, phrase, maxLen);
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| 116 | } else {
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| 117 | char nt = phrase.FirstNonTerminal;
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| 118 |
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| 119 | 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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| 120 | Debug.Assert(maxLenOfReplacement > 0);
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| 121 |
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| 122 | var alts = g.GetAlternatives(nt).Where(alt => g.MinPhraseLength(alt) <= maxLenOfReplacement);
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| 123 |
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| 124 | if (n.randomTries == randomTries && n.children == null) {
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| 125 | n.children = alts.Select(alt => new TreeNode(alt.ToString())).ToArray(); // create a new node for each alternative
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| 126 | treeSize += n.children.Length;
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| 127 | }
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| 128 | // => select using bandit policy
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| 129 | int selectedAltIdx = SelectAction(random, n.children);
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| 130 | Sequence selectedAlt = alts.ElementAt(selectedAltIdx);
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| 131 |
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| 132 | // replace nt with alt
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| 133 | phrase.ReplaceAt(phrase.FirstNonTerminalIndex, 1, selectedAlt);
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| 134 |
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| 135 | curDepth++;
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| 136 |
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| 137 | // prepare for next iteration
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| 138 | n = n.children[selectedAltIdx];
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| 139 | }
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| 140 | } // while
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| 141 |
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| 142 | updateChain.Add(n);
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| 143 |
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| 144 |
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| 145 | // the last node is a leaf node (sentence is done), so we never need to visit this node again
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| 146 | n.done = true;
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| 147 |
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| 148 | treeDepth = Math.Max(treeDepth, curDepth);
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| 149 | return phrase;
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| 150 | }
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| 151 |
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| 152 |
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| 153 | // eps-greedy
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| 154 | private int SelectAction(Random random, TreeNode[] children) {
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| 155 | if (random.NextDouble() < 0.1) {
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| 156 |
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| 157 | return children.Select((ch, i) => Tuple.Create(ch, i)).Where(p => !p.Item1.done).SelectRandom(random).Item2;
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| 158 | } else {
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| 159 | var bestQ = double.NegativeInfinity;
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| 160 | var bestChildIdx = -1;
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| 161 | for (int i = 0; i < children.Length; i++) {
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| 162 | if (children[i].done) continue;
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| 163 | if (children[i].tries == 0) return i;
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| 164 | if (children[i].q > bestQ) {
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| 165 | bestQ = children[i].q;
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| 166 | bestChildIdx = i;
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| 167 | }
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| 168 | }
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| 169 | Debug.Assert(bestChildIdx > -1);
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| 170 | return bestChildIdx;
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| 171 | }
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| 172 | }
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| 173 |
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| 174 | private void DistributeReward(double reward) {
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| 175 | const double alpha = 0.1;
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| 176 | const double gamma = 1;
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| 177 | // iterate in reverse order (bottom up)
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| 178 | updateChain.Reverse();
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| 179 | var nextQ = 0.0;
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| 180 | foreach (var e in updateChain) {
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| 181 | var node = e;
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| 182 | node.tries++;
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| 183 | if (node.children != null && node.children.All(c => c.done)) {
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| 184 | node.done = true;
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| 185 | }
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| 186 | // reward is recieved only for the last action
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| 187 | if (e == updateChain.First()) {
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| 188 | node.q = node.q + alpha * (reward + gamma * nextQ - node.q);
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| 189 | nextQ = node.q;
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| 190 | } else {
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| 191 | node.q = node.q + alpha * (0 + gamma * nextQ - node.q);
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| 192 | nextQ = node.q;
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| 193 | }
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| 194 | }
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| 195 | }
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| 196 |
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| 197 | private void RaiseSolutionEvaluated(string sentence, double quality) {
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| 198 | var handler = SolutionEvaluated;
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| 199 | if (handler != null) handler(sentence, quality);
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| 200 | }
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| 201 | private void RaiseFoundNewBestSolution(string sentence, double quality) {
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| 202 | var handler = FoundNewBestSolution;
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| 203 | if (handler != null) handler(sentence, quality);
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| 204 | }
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| 205 | }
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| 206 | }
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