/// <summary>
/// Whether to compute smoothing probabilities using the ForwardBackwardAlgorithm
/// for the states of the most likely sequence. Note that this significantly increases
/// computation time and memory footprint. <br/>
/// Must be called before processing is started.
/// </summary>
/// <param name="isComputeSmoothingProbabilities">Default: false</param>
/// <returns></returns>
public ViterbiModel <TState, TObservation, TDescriptor> SetComputeSmoothingProbabilities(bool isComputeSmoothingProbabilities)
{
if (this.IsProcessingStarted)
{
throw new InvalidOperationException("Processing has already started.");
}
if (isComputeSmoothingProbabilities)
{
_forwardBackward = new ForwardBackwardModel <TState, TObservation>();
}
else
{
_forwardBackward = null;
}
return(this);
}
public void testForwardBackward()
{
List <Rain> candidates = new List <Rain>();
candidates.Add(Rain.T);
candidates.Add(Rain.F);
var initialStateProbabilities = new Dictionary <Rain, double>();
initialStateProbabilities.Add(Rain.T, 0.5);
initialStateProbabilities.Add(Rain.F, 0.5);
var emissionProbabilitiesForUmbrella = new Dictionary <Rain, double>();
emissionProbabilitiesForUmbrella.Add(Rain.T, 0.9);
emissionProbabilitiesForUmbrella.Add(Rain.F, 0.2);
var emissionProbabilitiesForNoUmbrella = new Dictionary <Rain, double>();
emissionProbabilitiesForNoUmbrella.Add(Rain.T, 0.1);
emissionProbabilitiesForNoUmbrella.Add(Rain.F, 0.8);
var transitionProbabilities = new Dictionary <Transition <Rain>, double>();
transitionProbabilities.Add(new Transition <Rain>(Rain.T, Rain.T), 0.7);
transitionProbabilities.Add(new Transition <Rain>(Rain.T, Rain.F), 0.3);
transitionProbabilities.Add(new Transition <Rain>(Rain.F, Rain.T), 0.3);
transitionProbabilities.Add(new Transition <Rain>(Rain.F, Rain.F), 0.7);
var fw = new ForwardBackwardModel <Rain, Umbrella>();
fw.Start(candidates, initialStateProbabilities);
fw.NextStep(Umbrella.T, candidates, emissionProbabilitiesForUmbrella,
transitionProbabilities);
fw.NextStep(Umbrella.T, candidates, emissionProbabilitiesForUmbrella,
transitionProbabilities);
fw.NextStep(Umbrella.F, candidates, emissionProbabilitiesForNoUmbrella,
transitionProbabilities);
fw.NextStep(Umbrella.T, candidates, emissionProbabilitiesForUmbrella,
transitionProbabilities);
fw.NextStep(Umbrella.T, candidates, emissionProbabilitiesForUmbrella,
transitionProbabilities);
var result = fw.ComputeSmoothingProbabilities();
Assert.Equal(6, result.Count);
var DELTA = 4; //1e-4;
Assert.Equal(0.6469, result[0][Rain.T], DELTA);
Assert.Equal(0.3531, result[0][Rain.F], DELTA);
Assert.Equal(0.8673, result[1][Rain.T], DELTA);
Assert.Equal(0.1327, result[1][Rain.F], DELTA);
Assert.Equal(0.8204, result[2][Rain.T], DELTA);
Assert.Equal(0.1796, result[2][Rain.F], DELTA);
Assert.Equal(0.3075, result[3][Rain.T], DELTA);
Assert.Equal(0.6925, result[3][Rain.F], DELTA);
Assert.Equal(0.8204, result[4][Rain.T], DELTA);
Assert.Equal(0.1796, result[4][Rain.F], DELTA);
Assert.Equal(0.8673, result[5][Rain.T], DELTA);
Assert.Equal(0.1327, result[5][Rain.F], DELTA);
}
