86 lines
2.4 KiB
C#
86 lines
2.4 KiB
C#
using BotSharp.Algorithm.HiddenMarkovModel.Helpers;
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using System;
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using System.Collections.Generic;
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using System.Linq;
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using System.Text;
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namespace BotSharp.Algorithm.HiddenMarkovModel
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{
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public partial class Viterbi
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{
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public int[] LogForward(double[,] logA, double[,] logB, double[] logPi, int[] observations)
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{
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double logLikelihood = 0;
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return LogForward(logA, logB, logPi, observations, out logLikelihood);
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}
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public static int[] LogForward(double[,] logA, double[,] logB, double[] logPi, int[] observations, out double logLikelihood)
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{
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int T = observations.Length;
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int N = logPi.Length;
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DiagnosticsHelper.Assert(logA.GetLength(0) == N);
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DiagnosticsHelper.Assert(logA.GetLength(1) == N);
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DiagnosticsHelper.Assert(logB.GetLength(0) == N);
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int[,] V = new int[T, N];
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double[,] fwd = new double[T, N];
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for (int i = 0; i < N; ++i)
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{
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fwd[0, i] = logPi[i] + logB[i, observations[0]];
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}
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double maxWeight = 0;
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int maxState = 0;
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for (int t = 1; t < T; ++t)
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{
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for (int i = 0; i < N; ++i)
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{
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maxWeight = fwd[t - 1, 0] + logA[0, i];
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maxState = 0;
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double weight = 0;
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for (int j = 1; j < N; ++j)
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{
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weight = fwd[t - 1, j] + logA[j, i];
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if (maxWeight < weight)
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{
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maxWeight = weight;
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maxState = j;
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}
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}
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fwd[t, i] = maxWeight + logB[i, observations[t]];
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V[t, i] = maxState;
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}
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}
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maxState = 0;
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maxWeight = fwd[T - 1, 0];
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for (int i = 0; i < N; ++i)
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{
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if (fwd[T - 1, i] > maxWeight)
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{
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maxWeight = fwd[T - 1, i];
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maxState = i;
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}
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}
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int[] path = new int[T];
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path[T - 1] = maxState;
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for (int t = T - 2; t >= 0; --t)
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{
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path[t] = V[t + 1, path[t + 1]];
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}
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logLikelihood = maxWeight;
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return path;
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}
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}
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}
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