source: branches/HeuristicLab.Algorithms.IteratedSentenceConstruction/HeuristicLab.Algorithms.IteratedSymbolicExpressionConstruction/3.3/Policies/BoltzmannExplorationSymbolicExpressionConstructionPolicy.cs @ 12967

using System;
using System.Collections.Generic;
using System.Linq;
using HeuristicLab.Common;
using HeuristicLab.Core;
using HeuristicLab.Data;
using HeuristicLab.Encodings.SymbolicExpressionTreeEncoding;
using HeuristicLab.Parameters;
using HeuristicLab.Persistence.Default.CompositeSerializers.Storable;
using HeuristicLab.PluginInfrastructure;
using HeuristicLab.Random;

namespace HeuristicLab.Algorithms.IteratedSymbolicExpressionConstruction {
  [StorableClass]
  [Item("BoltzmannExplorationSymbolicExpressionConstructionPolicy", "")]
  public class BoltzmannExplorationSymbolicExpressionConstructionPolicy : SymbolicExpressionConstructionPolicyBase {
    public double Beta {
      get { return ((IFixedValueParameter<DoubleValue>)Parameters["Beta"]).Value.Value; }
      set { ((IFixedValueParameter<DoubleValue>)Parameters["Beta"]).Value.Value = value; }
    }

    public IStateValueFunction StateValueFunction {
      get {
        return ((IValueParameter<IStateValueFunction>)Parameters["Quality function"]).Value;
      }
      set { ((IValueParameter<IStateValueFunction>)Parameters["Quality function"]).Value = value; }
    }


    protected BoltzmannExplorationSymbolicExpressionConstructionPolicy(BoltzmannExplorationSymbolicExpressionConstructionPolicy original, Cloner cloner)
      : base(original, cloner) {
    }

    [StorableConstructor]
    protected BoltzmannExplorationSymbolicExpressionConstructionPolicy(bool deserializing) : base(deserializing) { }


    public BoltzmannExplorationSymbolicExpressionConstructionPolicy()
      : base() {
      Parameters.Add(new FixedValueParameter<DoubleValue>("Beta", "The weighting factor beta", new DoubleValue(1.0)));
      Parameters.Add(new ValueParameter<IStateValueFunction>("Quality function", "The quality function to use", new TabularAvgStateValueFunction()));
    }

    protected sealed override int Select(IReadOnlyList<object> followStates, IRandom random) {
      var idxs = Enumerable.Range(0, followStates.Count);

      // windowing
      var max = followStates.Select(s => StateValueFunction.Value(s)).Max();
      var min = followStates.Select(s => StateValueFunction.Value(s)).Min();
      double range = max - min;
      if (range.IsAlmost(0.0)) return idxs.SampleRandom(random);

      var w = from s in followStates
              select Math.Exp(Beta * (StateValueFunction.Value(s) - min) / range);

      return idxs.SampleProportional(random, 1, w).First();

    }

    public sealed override void Update(IEnumerable<object> stateSequence, double quality) {
      foreach (var state in stateSequence) {
        StateValueFunction.Update(state, quality);
      }
    }

    protected override object CreateState(ISymbolicExpressionTreeNode root, List<ISymbol> actionSequence, ISymbolicExpressionTreeNode parent, int childIdx) {
      return StateValueFunction.StateFunction.CreateState(root, actionSequence, parent, childIdx);
    }

    public override IDeepCloneable Clone(Cloner cloner) {
      return new BoltzmannExplorationSymbolicExpressionConstructionPolicy(this, cloner);
    }
  }
}