ladapt.tex

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% HTKBook - Valtcho Valtchev    04/02/98
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% Updated - Gareth Moore        15/01/02 - 1/3/02
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\newpage
\mysect{LAdapt}{LAdapt}

\mysubsect{Function}{Function}

\index{ladapt@\htool{LAdapt}|(}
This program will adapt an existing language model from supplied text
data.  This is accomplished in two stages. First, the text data is
scanned and a new language model is generated. In the second stage, an
existing model is loaded and adapted (merged) with the newly created
one according to the specified ratio.  The target model can be
optionally pruned to a specific vocabulary.  Note that you can only
apply this tool to word models or the class $n$-gram component of a
class model -- that is, you cannot apply it to full class models.

\mysubsect{Use}{LAdapt-Use}

\htool{LAdapt} is invoked by the command line
\begin{verbatim}
   LAdapt [options] -i weight inLMFile outLMFile [texttfile ...]
\end{verbatim}
The text data is scanned and a new LM generated. The input language model is
then loaded and the two models merged. The effect of the weight (0.0-1.0) is to
control the overall contribution of each model during the merging process. The
output to outLMFile is an $n$-gram model stored in the user-specified format.

The allowable options to \htool{LAdapt} are as follows
\begin{optlist}
  \ttitem{-a n} Allow upto \texttt{n} new words in input text
        (default 100000).

  \ttitem{-b n} Set the $n$-gram buffer size to $n$. This controls the size of the
	buffer used to accumulate $n$-gram statistics whilst scanning the input
	text.  Larger buffer sizes will result in more efficient operation of
	the tool with fewer sort operations required (default 2000000).

  \ttitem{-c n c} Set the pruning threshold for $n$-grams to $c$.  Pruning can
	be applied to the bigram ($n$=2) and longer ($n$>2) components of the
	newly generated model. The pruning procedure will keep only $n$-grams
	which have been observed more than $c$ times.

  \ttitem{-d s} Set the root $n$-gram data file name to {\tt s}. By default,
  	$n$-gram statistics from the text data will be accumulated and stored
  	as {\tt gram.0, gram.1, ...}, etc. Note that a larger buffer size will
  	result in fewer files.
        
  \ttitem{-f s} Set the output language model format to {\tt s}.
        Possible options are {\tt text} for the standard ARPA-MIT
	LM format, {\tt bin} for Entropic {\em binary} format and 
        {\tt ultra} for Entropic {\em ultra} format.

  \ttitem{-g} Use existing $n$-gram data files. If this option is specified the
	tool will use the existing gram files rather than scanning the actual
	texts. This option is useful when adapting multiple language models
	from the same text data or when experimenting with different merging
	weights.

  \ttitem{-i w f} Interpolate with model {\tt f} using weight {\tt w}. Note 
        that at least one model must be specified with this option.

  \ttitem{-j n c} Set weighted discounting pruning for $n$ grams to
        $c$. This cannot be applied to unigrams ($n$=1).

  \ttitem{-n n} Produce $n$-gram language model.

  \ttitem{-s s} Store {\tt s} in the header of the gram files.

  \ttitem{-t} Force Turing-Good discounting if configured otherwise.

  \ttitem{-w fn} Load word list from {\tt fn}. The word list will be used to
	define the target model's vocabulary. If a word list is not specified,
	the target model's vocabulary will have all words from the source
	model(s) together with any new words encountered in the text
	data.

  \ttitem{-x} Create a count-based model.
\end{optlist}
\stdopts{LAdapt}

\mysubsect{Tracing}{LAdapt-Tracing}

\htool{LAdapt} supports the following trace options where each trace flag is 
given using an octal base
\begin{optlist}
  \ttitem{00001}  basic progress reporting
  \ttitem{00002}  monitor buffer saving
  \ttitem{00004}  trace word input stream
  \ttitem{00010}  trace shift register input
\end{optlist}
Trace flags are set using the \texttt{-T} option or the \texttt{TRACE}
configuration variable.
\index{ladapt@\htool{LAdapt}|)}