Forward–backward algorithm: Difference between revisions

Revision as of 21:03, 27 February 2013

Revision as of 13:45, 5 April 2013

Line 332:

# Initialize base fwd cases

prev_f_sum = a_0[st]

else:

prev_f_sum = sum(f_prev[k]*a[k][st] for k in states)

f_curr[st] = e[st][x_i] * prev_f_sum

fwd.append(f_curr)

f_prev = f_curr

Line 345 ⟶ 341:

b_prev = {}

# Run bkw

for i, x_i_plus in enumerate(reversed(x[1:]+(None,))):

b_curr = {}

for st in states:

if i == 0:

# Initialize base bkw cases

b_curr[st] = a[st][end_st]

else:

b_curr[st] = sum(a[st][l]*e[l][x_i_plus]*b_prev[l] for l in states)

bkw.insert(0,b_curr)

b_prev = b_curr

p_bkw = sum(a_0[l] * e[l][x[0]] * b_curr[l] for l in states)