[SRILM User List] How do you calculate perplexity given a test sentence?

[Burkay Gur]

Hi,

I was wondering how the perplexity is calculated given different test 
sentences to a single language model.

1) For example, does SRI calculate 2^-H(p) no matter what the input 
sentence is ?

2) Or does it calculate the perplexity based on the cross-entropy 
between the model and the input sentence? ie 2^-H(p,q) where p is the 
language model and q is (not sure what it would be)

Best,
Burkay