[SRILM User List] harmonizing results with/without '-use-server'

[Andreas Stolcke]

In message <4DACADB5.2060700 at isi.edu>you wrote:
> 
> Testing on a rather small language model, I notice that I get
> different results for a given input lattice/pfsg depending on whether
> I interrogate the LM directly on the command line or resident in a
> server.
> 
> Precisely, the server is started thus:
> 
>    ngram -lm data/lm5a.lm -unk -server-port 2525
> 
> and then invoked via a command such as
> 
>    lattice-tool -in-lattice simple.pfsg -use-server 2525 at cent64.isi.edu 
> -nbest-decode 10 -out-nbest-dir server-out/
> 
> while the command line version is invoked thus:
> 
>    lattice-tool -unk -in-lattice simple.pfsg -lm data/lm5a.lm 
> -nbest-decode 10 -out-nbest-dir cmdline-out/
> 
> It's my intention and understanding that these two would be
> equivalent, but they are not.  As far as I can tell, the nature of the
> discrepancy is that the server generates only acoustic probabilities,
> no LM probabilities (well, they are all 0).  Also the order of
> returned results is different, but that very well could be due to the
> former issue.  Finally, the acoustic probabilities are are equal
> (within a 10-best window) in the server-based case, but vary slightly
> in the command line-based case.
> 
> I'd like to have results equivalent to the command-line invocation,
> but with the potential speedup provided by the
> -server-port/-use-server case.  Is this possible, and if so, which
> parameter adjustments do I need to make?

Andrew,

due to a bug, the -use-server LM was completely ignored in nbest generation.
The patch below will fix this and should give you the expected results.

Andreas

diff -c -r1.155 lattice-tool.cc
*** lattice/src/lattice-tool.cc	29 Jan 2011 05:56:35 -0000	1.155
--- lattice/src/lattice-tool.cc	19 Apr 2011 00:25:54 -0000
***************
*** 544,550 ****
      }
  
      if (viterbiDecode) {
!         LM *plm = lmFile ? &lm : 0;
  
  	if (outputCTM) {
  	    NBestWordInfo *bestwords = new NBestWordInfo[maxWordsPerLine + 1];
--- 544,550 ----
      }
  
      if (viterbiDecode) {
!         LM *plm = (lmFile || useServer) ? &lm : 0;
  
  	if (outputCTM) {
  	    NBestWordInfo *bestwords = new NBestWordInfo[maxWordsPerLine + 1];
***************
*** 610,616 ****
  				 nbestMaxHyps, nbestDuplicates);
  	    }
  	} else {
! 	    LM *plm = lmFile ? &lm : 0;	  
  	    lat.decodeNBest(nbestDecode, nbestOut, noiseWords, plm,
  	    		    order, maxDegree, 
  			    beamwidth > 0.0 ?
--- 610,616 ----
  				 nbestMaxHyps, nbestDuplicates);
  	    }
  	} else {
! 	    LM *plm = (lmFile || useServer) ? &lm : 0;	  
  	    lat.decodeNBest(nbestDecode, nbestOut, noiseWords, plm,
  	    		    order, maxDegree, 
  			    beamwidth > 0.0 ?