/// <summary>
/// Returns a random index of the matrix state column using the given distribution.
/// </summary>
/// <param name="state">Current state.</param>
/// <param name="matrix">Probability distribution matrix.</param>
/// <returns>Random index of the matrix state column.</returns>
private int randomExtraction(int state, MySparse2DMatrix matrix)
{
var rand = SystemRandomSource.Default;
var extraction = rand.NextDouble();
for (int i = 0; i < Symbols; i++)
{
if (extraction < matrix.getValue(state, i))
{
return(i);
}
extraction -= matrix.getValue(state, i);
}
return(-1);
}
/// <summary>
/// Determining the frequency of the transition-emission pair values
/// and dividing it by the probability of the entire string.
///
/// Using the scaled values, I don't need to divide it for the
/// probability of the entire string anymore
/// </summary>
/// <param name="t">Current time.</param>
/// <param name="nextObservation">Observation at time t + 1.</param>
/// <returns>Probability of transition from each state to any other at time t</returns>
private MySparse2DMatrix calcXi(int t, int nextObservation)
{
if (tempInstancts == null)
{
throw new ArgumentNullException("tempInstancts");
}
if (tempInstancts[t].Alpha == null || tempInstancts[t].Beta == null)
{
throw new ArgumentNullException("Alpha and Beta aren't set");
}
MySparse2DMatrix currentXi = new MySparse2DMatrix();
double s = 0;
for (int i = 0; i < States; i++)
{
for (int j = 0; j < States; j++)
{
double temp = tempInstancts[t].Alpha[i] * Transitions.getValue(i, j) * Emissions.getValue(j, nextObservation) * tempInstancts[t + 1].Beta[j];
s += temp;
if (temp != 0)
{
currentXi.setValue(i, j, temp);
}
}
}
if (s != 0) // Scaling
{
for (int i = 0; i < States; i++)
{
for (int j = 0; j < States; j++)
{
if (currentXi.getValue(i, j) != 0)
{
currentXi.setValue(i, j, currentXi.getValue(i, j) / s);
}
}
}
}
return(currentXi);
}