source: branches/HeuristicLab.Algorithms.IteratedSentenceConstruction/HeuristicLab.Algorithms.IteratedSymbolicExpressionConstruction/3.3/QualityFunctions/SparseLinearApproximateStateValueFunction.cs @ 13553

using System;
using System.Collections;
using System.Collections.Generic;
using System.Linq;
using HeuristicLab.Common;
using HeuristicLab.Core;
using HeuristicLab.Parameters;
using HeuristicLab.Persistence.Default.CompositeSerializers.Storable;

namespace HeuristicLab.Algorithms.IteratedSymbolicExpressionConstruction {
  [StorableClass]
  public class SparseLinearApproximateStateValueFunction : ParameterizedNamedItem, IStateValueFunction, IStatefulItem {

    private readonly Dictionary<string, double> w = new Dictionary<string, double>();

    public IStateFunction StateFunction {
      get {
        return ((IValueParameter<IStateFunction>)Parameters["Feature function"]).Value;
      }
      private set { ((IValueParameter<IStateFunction>)Parameters["Feature function"]).Value = value; }
    }

    public SparseLinearApproximateStateValueFunction()
      : base() {
      Parameters.Add(new ValueParameter<IStateFunction>("Feature function", "The function that generates features for value approximation"));
    }

    public double Value(object state) {
      var features = state as IEnumerable<Tuple<string, double>>;
      if (features == null) throw new InvalidProgramException();

      return features.Select(t => t.Item2 * GetWeight(t.Item1)).Sum();
    }

    private double GetWeight(string featureId) {
      double w;
      this.w.TryGetValue(featureId, out w);
      return w;
    }

    public void Update(object state, double observedQuality) {
      var features = state as IEnumerable<Tuple<string, double>>;
      if (features == null) throw new InvalidProgramException();

      var delta = observedQuality - Value(state);
      const double alpha = 0.01;

      foreach (var t in features) {
        var featureId = t.Item1;
        var w = t.Item2;

        this.w[featureId] = GetWeight(featureId) + alpha * delta;
      }
    }

    #region item
    [StorableConstructor]
    protected SparseLinearApproximateStateValueFunction(bool deserializing) : base(deserializing) { }
    protected SparseLinearApproximateStateValueFunction(SparseLinearApproximateStateValueFunction original, Cloner cloner)
      : base(original, cloner) {
      w = new Dictionary<string, double>(original.w);
    }

    public override IDeepCloneable Clone(Cloner cloner) {
      return new SparseLinearApproximateStateValueFunction(this, cloner);
    }
    #endregion

    public void InitializeState() {
      w.Clear();
    }

    public void ClearState() {
      w.Clear();
    }
  }
}