[SRILM User List] ARPA LM with only higher order grams?

[Amr Desoky]

Hi,
  I am asking is it possible to have an ARPA LM storing only 3-gram log 
probabilities?
  Assuming that in my application (in which I will use the LM), I will only 
require the probability of these specific 3-grams.
  example of the LM:

\data\
ngram 1=0
ngram 2=0
ngram 3=3

\1-grams:

\2-grams:

\3-grams:
<logprob> <w1 w2 w3>
<logprob> <w4 w5 w6>
<logprob> <w7 w8 w9>

\end\


To say in other words: if I got some method to estimate the probability of some 
3-grams needed for 3-gram lattice rescoring for ASR, is it possible to insert 
the probabilities of these 3-grams in a normal ARPA backoff LM? I did so, but 
when I tried to normalize the new LM (after adding the new 3-grams), I got the 
following warinings and the new grams are filtered out!

warning: no bow for prefix of ngram "w1 w2 w3"
.........(lots of the above warinig)
BOW numerator for context "w4 w5" is -0.535204 < 0
.........(lots of the above warinig)

could you tell me why this is happening? since if some 3-gram probability is 
there I will not need to backoff and I will not need to use the lower order 
grams to get the probability of this specific 3-gram...yes?

What if I did not normalize the new LM will it be a correct LM or you see some 
bug, is there some other way to validate the correctness of this LM?

I will appreciate your help very much.

Best regards,
Amr



 Amr Ibrahim El-Desoky, Mousa 
PhD Student, Computer Science (i6), 
RWTH-Aachen University, 
Aachen, Germany 
Cel.     : +49 0176 56418470 
Office : +49 241 8021620 
Fax      : +49 241 8022219



      
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