lfof.tex

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% HLMBook - Steve Young    13/01/97
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% Updated - Gareth Moore   15/01/02
%

\newpage
\mysect{LFoF}{LFoF}

\mysubsect{Function}{LFoF-Function}

\index{lFoF@\htool{LFoF}|(}
This program will read one or more input gram files and generate a
\textit{frequency-of-frequency} or \textit{FoF} file. A FoF file is a
list giving the number of times that an $n$-gram occurs just once, the
number of times that an $n$-gram occurs just twice, etc. The format of a
FoF file is described in section~\ref{s:FoFs}.\index{FoF file}

As for all tools which process gram files, the input gram files must
each be sorted but they need not be sequenced. The counts in each
input file can be modified by applying a multiplier factor.  Any $n$-gram
containing an id which is not in the word map is ignored, thus, the
supplied word map will typically contain just those word and class ids
required for the language model under construction (see
\htool{LSubset}).

\htool{LFoF} also provides an option to generate an estimate
of the number of $n$-grams which would be included in the final language
model for each possible cutoff by setting \texttt{LPCALC: TRACE = 2}.

\mysubsect{Use}{LFoF-Use}

\htool{LFoF} is invoked by typing the command line
\begin{verbatim}
   LFoF [options] wordmap foffile [mult] gramfile .. [mult] gramfile ..
\end{verbatim}
The given word map file is loaded and then the set of named gram files
are merged to form a single sorted stream of $n$-grams. Any $n$-grams
containing ids not in the word map are ignored. The list of input gram
files can be interspersed with multipliers. These are floating-point
format numbers which must begin with a plus or minus character
(e.g. \texttt{+1.0}, \texttt{-0.5}, etc.). The effect of a multiplier
\texttt{x} is to scale the $n$-gram counts in the following gram files by
the factor \texttt{x}.  A multiplier stays in effect until it is
redefined.  The output to \texttt{foffile} is a FoF file as described
in section~\ref{s:FoFs}.

The allowable options to \htool{LFoF} are as follows

\begin{optlist}
  \ttitem{-f N} set the number of FoF entries to N (default 100).
  \ttitem{-n N} Set $n$-gram size to \texttt{N} (defaults to max).
\end{optlist}
\stdopts{LFoF}


\mysubsect{Tracing}{LFoF-Tracing}

\htool{LFoF} supports the following trace options where each
trace flag is given using an octal base
\begin{optlist}
\ttitem{00001}  basic progress reporting
%\ttitem{00002}  print FoF table every 100,000 input grams
\end{optlist}
Trace flags are set using the \texttt{-T} option or the  \texttt{TRACE} 
configuration variable.
\index{lFoF@\htool{LFoF}|)}