some tech queries
Gill Bejerano
jill at cs.huji.ac.il
Sun Apr 7 17:43:16 PDT 2002
Hi,
I am new to SRILM, and quite new to language modelling at large
(coming from other domains of n-gram models usage).
I have run some perliminary probes with SRILM (on linux, smooth install)
and have the following questions:
1. in ngram-count:
when using -lm with the default -order 3, i had expected -text <textfile>
to yield the same model as -read <order1> -read <order2> -read <order3>
where order{1-3} have been obtained through ngram-count -write{1-3}
(all other paramters being equal). and yet the two LM files differ.
how come?
2. in ngram-count:
i'm not quite clear about the multiple -cdiscount flags.
suppose i want a default -order 3 LM.
mustn't i give all three D's and have the model interpolate over all
of these, as eq. (18) in Chen&Goodman (p.15) implies?
in practice it seems one can specify any subset of the 3 and get
different models. (are there default Ds?)
3. in ngram-count:
probably closely related to question 2.
(and prob. due to some confusion i have between backoff & interpolation)
why are there multiple -interpolate flags.
again, eq. (18) in C&G appears to imply a recursive all levels
interpolation. and yet ngram-count appears to take any subset of
-interpolate{1-3} (in the above example) and yield different LMs.
4. combining 2+3:
if i want an absolute discount model of order, say 3,
"by the book" C&G eq. (18), what is the proper way to run it?
assume i have ran ngram-count => get-gt-counts => make-abs-discount
and obtained <D1> <D2> <D3>.
a command line example will be highly appreciated.
5. ngram-count vs. ngram:
if i use ngram-count with some combination of -prune and -minprune
to obtain a model and then use ngram -ppl, will the result be identical
to running ngram-count without the pruning flags, and running ngram -ppl
on the new model with -prune -minprune as was previously done for model
building?
6. for ngram -ppl:
in -debug 1, i believe, two measures are given per sentence, ppl and ppl1.
how are they defined?
is one C&G's $PP_p(T)$ (p.9,top)? then, what is the other?
Help would be highly appreciated,
-Gill
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