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HMM.cs
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HMM.cs
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using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
namespace Master.Utility
{
/// <summary>
/// Class models hidden Markov model transition matrix
/// Author: Tomislav
/// </summary>
public class HMM
{
private List<Dictionary<List<int>, double[]>> ngramProbs;
/// <summary>
/// Constructor accepting N-gram probabilities of all N-gram orders
/// </summary>
/// <param name="ngramProbs">N-gram probabilities</param>
public HMM(List<Dictionary<List<int>, double[]>> ngramProbs) {
this.ngramProbs = ngramProbs;
}
/// <summary>
/// Method sets N-gram probabilities
/// </summary>
/// <param name="ngramProbs">N-gram probabilities</param>
public void setNgramProbs(List<Dictionary<List<int>, double[]>> ngramProbs) {
this.ngramProbs = ngramProbs;
}
/// <summary>
/// Method return N-gram probability
/// </summary>
/// <param name="ngram">N-gram</param>
/// <returns>N-gram probability</returns>
public double getStateToStateProb(List<int> ngram) {
int order = ngram.Count;
if (ngramProbs[order - 1].ContainsKey(ngram)) {
return Math.Log(ngramProbs[order - 1][ngram][0], 2);
}
else {
List<int> prefix = new List<int>(ngram);
double bow = 0;
while (true) {
prefix.RemoveAt(prefix.Count - 1);
if (ngramProbs[prefix.Count - 1].ContainsKey(prefix)) {
bow = Math.Log(ngramProbs[prefix.Count - 1][prefix][1], 2);
break;
}
}
List<int> lowerNgram = new List<int>(ngram);
lowerNgram.RemoveAt(0);
return bow + getStateToStateProb(lowerNgram);
}
}
/// <summary>
/// Method checks if N-gram exist in N-gram map
/// </summary>
/// <param name="ngram">N-gram</param>
/// <returns>True/false value depending if N-gram is found</returns>
public bool contains(List<int> ngram) {
return ngramProbs[ngram.Count - 1].ContainsKey(ngram);
}
}
}