public RandomVariable CalculateNextBackwardMessage(
RandomVariable forwardBelief,
RandomVariable presentBackwardMessage, string perception)
{
RandomVariable result = presentBackwardMessage.Duplicate();
// System.out.println("fb :-calculating new backward message");
// System.out.println("fb :-diagonal matrix from sens model = ");
Matrix oMatrix = this.SensorModel.AsMatrix(perception);
// System.out.println(oMatrix);
Matrix transitionMatrix = this.TransitionModel.AsMatrix();// action
// should
// be
// passed
// in
// here?
// System.out.println("fb :-present backward message = "
// +present_backward_message);
Matrix backwardMatrix = transitionMatrix.Times(oMatrix
.Times(presentBackwardMessage.AsMatrix()));
Matrix resultMatrix = backwardMatrix.ArrayTimes(forwardBelief
.AsMatrix());
result.UpdateFrom(resultMatrix);
result.Normalize();
// System.out.println("fb :-normalized new backward message = "
// +result);
return(result);
}
public List <RandomVariable> ForwardBackward(List <string> perceptions)
{
RandomVariable[] forwardMessages = new RandomVariable[perceptions.Count + 1];
RandomVariable backwardMessage = priorDistribution.CreateUnitBelief();
RandomVariable[] smoothedBeliefs = new RandomVariable[perceptions.Count + 1];
forwardMessages[0] = priorDistribution;
smoothedBeliefs[0] = null;
// populate forward messages
for (int i = 0; i < perceptions.Count; i++) // N.B i starts at 1,
// not zero
{
forwardMessages[i + 1] = this.Forward(forwardMessages[i], perceptions[i]);
}
for (int i = perceptions.Count; i > 0; i--)
{
RandomVariable smoothed = priorDistribution.Duplicate();
smoothed.UpdateFrom(forwardMessages[i].AsMatrix().ArrayTimes(
backwardMessage.AsMatrix()));
smoothed.Normalize();
smoothedBeliefs[i] = smoothed;
backwardMessage = this.CalculateNextBackwardMessage(
forwardMessages[i], backwardMessage, perceptions[i - 1]);
}
return(smoothedBeliefs.ToList());
}
public RandomVariable Smooth(String perception)
{
evidenceFromSmoothedStepToPresent.Add(perception);
Matrix oT = hmm.SensorModel.AsMatrix(perception);
Matrix transitionMatrix = hmm.TransitionModel.AsMatrix();
if (time > timelag)
{
forwardMessage = hmm.Forward(forwardMessage, perception); // This
// seems
// WRONG
// I think this should be
// forwardMessage = hmm.forward(forwardMessage,
// evidenceFromSmoothedStepToPresent.get(0));
// this the perception at t-d. the book's algorithm
// uses the latest perception.
evidenceFromSmoothedStepToPresent.RemoveAt(0);
Matrix oTMinusD = hmm.SensorModel.AsMatrix(
evidenceFromSmoothedStepToPresent[0]);
B = oTMinusD.Inverse().Times(
transitionMatrix.Inverse().Times(
B.Times(transitionMatrix.Times(oT))));
}
else
{
B = B.Times(transitionMatrix.Times(oT));
}
time += 1;
if (time > timelag)
{
Matrix one = hmm.Prior().CreateUnitBelief().AsMatrix();
Matrix forwardMatrix = forwardMessage.AsMatrix();
RandomVariable result = hmm.Prior().Duplicate();
Matrix backwardMessage = (B.Times(one));
result.UpdateFrom(forwardMatrix.ArrayTimes(backwardMessage));
result.Normalize();
return(result);
}
else
{
return(null);
}
}
public RandomVariable PerceptionUpdate(RandomVariable aBelief,
string perception)
{
RandomVariable newBelief = aBelief.Duplicate();
// one way - use matrices
Matrix beliefMatrix = aBelief.AsMatrix();
Matrix oMatrix = this.SensorModel.AsMatrix(perception);
Matrix updated = oMatrix.Times(beliefMatrix);
newBelief.UpdateFrom(updated);
newBelief.Normalize();
return(newBelief);
// alternate way of doing this. clearer in intent.
// for (string state : aBelief.states()){
// double probabilityOfPerception= sensorModel.get(state,perception);
// newBelief.setProbabilityOf(state,probabilityOfPerception *
// aBelief.getProbabilityOf(state));
// }
}
