mix LM

[Anand Venkataraman]

Hongqin

> fatal: division by zero attempted
> 
> The inputs for it were two ppl files from class and word based models,
> respectively by ngram ->
> 
> ./compute-best-mix /home/hliu/language_model/word/lm.word.3.ppl
> /home/hliu/language_model/class/lm.class.3.ppl

Did you make sure to use the -classes "file" option to expand classes while
computing ppls using the class lm?  If not, the EM algorithm could get
thrown off track by spurious probability values from the oovs.  In any
case, if you email the ppl output for the first sentence by each lm, we
could confirm what's going on.

&