1 | using System;
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2 | using System.Collections.Generic;
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3 | using System.Diagnostics.Contracts;
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4 | using System.Linq;
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5 | using System.Text;
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6 | using System.Threading.Tasks;
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7 | using HeuristicLab.Common;
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8 | using HeuristicLab.Core;
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9 | using HeuristicLab.Data;
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10 | using HeuristicLab.Parameters;
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11 |
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12 | namespace HeuristicLab.Algorithms.DataAnalysis.MctsSymbolicRegression.Policies {
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13 | [Item("EpsilonGreedy", "Epsilon greedy policy with parameter eps to balance between exploitation and exploration")]
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14 | public class EpsilonGreedy : PolicyBase {
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15 | private class ActionStatistics : IActionStatistics {
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16 | public double SumQuality { get; set; }
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17 | public double AverageQuality { get { return SumQuality / Tries; } }
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18 | public int Tries { get; set; }
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19 | public bool Done { get; set; }
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20 | }
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21 | private List<int> buf = new List<int>();
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22 |
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23 | public IFixedValueParameter<DoubleValue> EpsParameter {
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24 | get { return (IFixedValueParameter<DoubleValue>)Parameters["Eps"]; }
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25 | }
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26 |
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27 | public double Eps {
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28 | get { return EpsParameter.Value.Value; }
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29 | set { EpsParameter.Value.Value = value; }
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30 | }
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31 |
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32 | protected EpsilonGreedy(EpsilonGreedy original, Cloner cloner)
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33 | : base(original, cloner) {
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34 | }
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35 | public EpsilonGreedy()
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36 | : base() {
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37 | Parameters.Add(new FixedValueParameter<DoubleValue>("Eps", "Rate of random selection 0 (greedy) <= eps <= 1 (random)", new DoubleValue(0.1)));
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38 | }
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39 |
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40 | public override IDeepCloneable Clone(Cloner cloner) {
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41 | return new EpsilonGreedy(this, cloner);
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42 | }
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43 |
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44 | public override int Select(IEnumerable<IActionStatistics> actions, IRandom random) {
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45 | return Select(actions, random, Eps, buf);
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46 | }
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47 |
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48 | public override void Update(IActionStatistics action, double q) {
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49 | var a = action as ActionStatistics;
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50 | a.SumQuality += q;
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51 | a.Tries++;
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52 | }
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53 |
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54 | public override IActionStatistics CreateActionStatistics() {
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55 | return new ActionStatistics();
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56 | }
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57 |
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58 | private static int Select(IEnumerable<IActionStatistics> actions, IRandom rand, double c, IList<int> buf) {
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59 | buf.Clear();
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60 | if (rand.NextDouble() >= c) {
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61 | // select best
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62 | var bestQ = double.NegativeInfinity;
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63 | int aIdx = -1;
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64 | foreach (var a in actions) {
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65 | ++aIdx;
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66 | if (a.Done) continue;
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67 | var actionQ = a.Tries > 0 ? a.AverageQuality : double.PositiveInfinity; // always try unvisited actions first
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68 | if (actionQ > bestQ) {
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69 | buf.Clear();
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70 | buf.Add(aIdx);
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71 | bestQ = actionQ;
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72 | } else if (actionQ >= bestQ) {
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73 | buf.Add(aIdx);
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74 | }
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75 | }
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76 | return buf[rand.Next(buf.Count)];
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77 | } else {
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78 | // random selection
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79 | int aIdx = -1;
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80 | foreach (var a in actions) {
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81 | ++aIdx;
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82 | if (a.Done) continue;
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83 | buf.Add(aIdx);
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84 | }
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85 | return buf[rand.Next(buf.Count)];
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86 | }
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87 | }
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88 | }
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89 | }
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