LM missing back-off probabilities

[Goldee Udani]

Hi there,

I am sorry if this problem has already been addressed before on this forum.

I am trying to generate a small LM for using in Sphinx Speech 
Recognition system but the back-off probabilities for every ngram 
occuring at the end of sentence(s) are missing.
For example -

<s> we cannot afford to fight the war against poverty with accounting 
tricks </s>

For a trigram LM, it doesn't generate back-off probabilities for 
"tricks" (unigram) and "accounting tricks " (bigram). This tends to 
happen for all the sentences in the test set taken from the corpus.

I am trying to use the "ngram-count" script with witten bell discounting 
applied to all n-grams in a trigram model.

If any of you have faced a similar problem before, I would appreciate it 
if you could help me out here.

Thanks,
Goldee