lattice-tool and trigram

[Tanel Alumäe]

Hello,

I'm trying to expand word lattices with trigrams (and with factored LMs)
and find a best path (using -viterbi-decode). However, I'm quite
confused with the lattice-tool, because I cannot really understand what
it does - sometimes some parameters and options seem to be ignored. 

I have a word lattice produced with HTK (using bigram LM), and a trigram
LM in ARPA format.I run:
lattice-tool -lm trigram.arpa -in-lattice <in-lattice> -read-htk
-viterbi-decode 

When I try this, I get following output:
reading 60002 1-grams
reading 4038368 2-grams
reading 1184013 3-grams
Lattice::expandToLM: starting expansion to general LM (maxNodes = 0) ...
Lattice::bestWords: processing
Lattice::bestWords: best path prob = -inf
/home/tanel/devel/data/mfc/fts/sentences/aa/s10000_01.mfc </s>


Is this caused by the fact that there are !NULL nodes at the start and
end of the <in_lattice>? I tried adding the -no-htk-nulls -no-nulls
options but this doesn't seem to help...

Maybe somebody can provide a correct workflow to get a  trigram-scored
best path from HTK lattices using lattice-tool?

Thanks and best regards,

Tanel Alumäe