?? backward.c
字號:
#include <stdio.h>
#include "hmm.h"
void Backward(HMM *phmm, int T, int *O, double **beta, double *pprob)
{
int i, j;
int t;
double sum;
for (i = 1; i <= phmm->N; i++)
beta[T][i] = 1.0;
for (t = T - 1; t >= 1; t--)
{
for (i = 1; i <= phmm->N; i++)
{
sum = 0.0;
for (j = 1; j <= phmm->N; j++)
sum += phmm->A[i][j] * (phmm->B[j][O[t+1]])*beta[t+1][j];
beta[t][i] = sum;
}
}
*pprob = 0.0;
for (i = 1; i <= phmm->N; i++)
*pprob += beta[1][i];
}
void BackwardWithScale(HMM *phmm, int T, int *O, double **beta, double *scale, double *pprob)
{
int i, j;
int t;
double sum;
for (i = 1; i <= phmm->N; i++)
beta[T][i] = 1.0/scale[T];
for (t = T - 1; t >= 1; t--)
{
for (i = 1; i <= phmm->N; i++)
{
sum = 0.0;
for (j = 1; j <= phmm->N; j++)
sum += phmm->A[i][j] * (phmm->B[j][O[t+1]])*beta[t+1][j];
beta[t][i] = sum/scale[t];
}
}
}
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