asr_utils.py

import alex_asr.fst as fst
from math import *

def lattice_calibration(lat):
    def find_approx(weight):
        calibration_table = [
            (0.999999999999975, 2.0, 0.88018348094713794),
            (0.9999999999961884, 0.999999999999975, 0.80349730129423402),
            (0.999999999830834, 0.9999999999961884, 0.73428284555412904),
            (0.9999999953944774, 0.999999999830834, 0.67181212520944233),
            (0.9999999061531399, 0.9999999953944774, 0.61542808146230965),
            (0.9999985463132696, 0.9999999061531399, 0.5645376743766013),
            (0.9999801852444311, 0.9999985463132696, 0.51860564536208376),
            (0.9997798377111068, 0.9999801852444311, 0.47714888739515909),
            (0.9979068550339635, 0.9997798377111068, 0.43973136376290312),
            (0.9855103527780578, 0.9979068550339635, 0.40595952188642426),
            (0.9107043589029054, 0.9855103527780578, 0.37547815398674106),
            (0.6495785364198595, 0.9107043589029054, 0.34796666105620766),
            (0.29778636903306327, 0.6495785364198595, 0.32313568084043276),
            (0.08195954925619552, 0.29778636903306327, 0.30072404436424938),
            (0.017934535127822632, 0.08195954925619552, 0.28049602899087711),
            (0.0008663571990016966, 0.017934535127822632, 0.24576056846402694),
            (4.3793087001897236e-05, 0.0008663571990016966, 0.21746408465901332),
            (2.438732279388375e-06, 4.3793087001897236e-05, 0.19441297252222531),
            (3.773110309325966e-08, 2.438732279388375e-06, 0.16759461792800706),
            (1.898540256696829e-10, 3.773110309325966e-08, 0.14254056133908768),
            (9.034359693017792e-14, 1.898540256696829e-10, 0.11983387028320044),
            (3.668374817174373e-20, 9.034359693017792e-14, 0.099474926398142052),
            (0.0, 3.668374817174373e-20, 0.096552470524865874),
        ]

        for i, (min, max, p) in enumerate(calibration_table):
            if min <= weight < max:
                return p

        print "Lattice calibration warning: cannot map input score."
        return weight

    for state in lat.states:
        cum = 0.0
        for arc in state.arcs:
            weight = exp(-float(arc.weight))
            aprx = find_approx(weight)
            cum +=aprx
            arc.weight = fst.LogWeight(-log(aprx))

        for arc in state.arcs:
            arc.weight = fst.LogWeight( -log(exp(-float(arc.weight)) / cum) )
    return lat