empty-sentence-lm

这是一款很好用的工具包

#!/bin/sh
#
# empty-sentence-lm --
#	modify language model to allow the empty sentence.
#	This adds a "<s> </s>" bigram to the model and scales the 
#	probabilities of other bigrams starting with <s>.
#	probabilities.  Backoff weights are recomputed.
#
# usage: empty-sentence-lm -prob P -lm oldlm -write-lm newlm
#
# $Header: /home/srilm/devel/utils/src/RCS/empty-sentence-lm,v 1.3 2003/08/20 16:34:16 stolcke Exp $
#

oldlm=-
newlm=-
prob=0.1
vocab=/dev/null
norm_option=-renorm

while [ $# -gt 0 ]; do
	case "$1" in
	-prob)	prob="$2" ; shift ;;
	-lm)	oldlm="$2" ; shift ;;
	-write-lm)	newlm="$2" ; shift ;;
	-nonorm) norm_option= ; shift ;;
	*)	options="$options $1" ;;
	esac
	shift
done

gunzip -cf $oldlm | gawk '
function log10(x) {
        return log(x)/2.30258509299404568402;
}

/^ngram 2=/ {
	num = substr($2, 3);
	print "ngram 2=" num + 1;
	next;
}

#
# add empty-sentence bigram
#
/^\\2-grams:/ {
	print;
	print log10(prob), "<s> </s>";
	in_ngrams = 2;
	next;
}

#
# ensure that <s> has backoff weight and 
# approximately adjust it (correct adjustment done by ngram -renorm)
#
in_ngrams == 1 && $2 == "<s>" {
	$3 += log10(1-prob);
}

#
# scale bigram probs starting with <s>
#
in_ngrams == 2 && $2 == "<s>" {
	$1 += log10(1-prob);
}

/^\\1-grams:/ {
	in_ngrams = 1;
}

/^\\3-grams:/ {
	in_ngrams = 3;
}

{
	print;
}' prob=$prob | \
ngram -lm - $norm_option -write-lm "$newlm" $options