=head1 NAME
Text::NSP::Measures::2D::MI::tmi - Perl module that implements True Mutual
Information.
=head1 SYNOPSIS
=head3 Basic Usage
use Text::NSP::Measures::2D::MI::tmi;
my $npp = 60; my $n1p = 20; my $np1 = 20; my $n11 = 10;
$tmi_value = calculateStatistic( n11=>$n11,
n1p=>$n1p,
np1=>$np1,
npp=>$npp);
if( ($errorCode = getErrorCode()))
{
print STDERR $errorCode." - ".getErrorMessage()."\n"";
}
else
{
print getStatisticName."value for bigram is ".$tmi_value."\n"";
}
=head1 DESCRIPTION
Assume that the frequency count data associated with a bigram
is stored in a 2x2 contingency table:
word2 ~word2
word1 n11 n12 | n1p
~word1 n21 n22 | n2p
--------------
np1 np2 npp
where n11 is the number of times occur together, and
n12 is the number of times occurs with some word other than
word2, and n1p is the number of times in total that word1 occurs as
the first word in a bigram.
The expected values for the internal cells are calculated by taking the
product of their associated marginals and dividing by the sample size,
for example:
np1 * n1p
m11= ---------
npp
True Mutual Information (tmi) is defined as the weighted average of the
Pointwise mutual informations for all the observed and expected value pairs.
tmi = [n11/npp * log(n11/m11) + n12/npp * log(n12/m12) +
n21/npp * log(n21/m21) + n22/npp * log(n22/m22)]
PMI = log (n11/m11)
=head2 Methods
=over
=cut
package Text::NSP::Measures::2D::MI::tmi;
use Text::NSP::Measures::2D::MI;
use strict;
use Carp;
use warnings;
no warnings 'redefine';
require Exporter;
our ($VERSION, @EXPORT, @ISA);
@ISA = qw(Exporter);
@EXPORT = qw(initializeStatistic calculateStatistic
getErrorCode getErrorMessage getStatisticName);
$VERSION = '0.97';
=item calculateStatistic() - This method calculates the tmi value
INPUT PARAMS : $count_values .. Reference of an hash containing
the count values computed by the
count.pl program.
RETURN VALUES : $tmi .. TMI value for this bigram.
=cut
sub calculateStatistic
{
my %values = @_;
# computes and returns the observed and expected values from
# the frequency combination values. returns 0 if there is an
# error in the computation or the values are inconsistent.
if( !(Text::NSP::Measures::2D::MI::getValues(\%values)) ) {
return(0);
}
#my $marginals = $self->computeMarginalTotals(@_);
# Now for the actual calculation of TMI!
my $tmi = 0;
# dont want ($nxy / $mxy) to be 0 or less! flag error if so!
$tmi += $n11/$npp * Text::NSP::Measures::2D::MI::computePMI( $n11, $m11 )/ log 2;
$tmi += $n12/$npp * Text::NSP::Measures::2D::MI::computePMI( $n12, $m12 )/ log 2;
$tmi += $n21/$npp * Text::NSP::Measures::2D::MI::computePMI( $n21, $m21 )/ log 2;
$tmi += $n22/$npp * Text::NSP::Measures::2D::MI::computePMI( $n22, $m22 )/ log 2;
return ($tmi);
}
=item getStatisticName() - Returns the name of this statistic
INPUT PARAMS : none
RETURN VALUES : $name .. Name of the measure.
=cut
sub getStatisticName
{
return "True Mutual Information";
}
1;
__END__
=back
=head1 AUTHOR
Ted Pedersen, University of Minnesota Duluth
Etpederse@d.umn.eduE
Satanjeev Banerjee, Carnegie Mellon University
Esatanjeev@cmu.eduE
Amruta Purandare, University of Pittsburgh
Eamruta@cs.pitt.eduE
Bridget Thomson-McInnes, University of Minnesota Twin Cities
Ebthompson@d.umn.eduE
Saiyam Kohli, University of Minnesota Duluth
Ekohli003@d.umn.eduE
=head1 HISTORY
Last updated: $Id: tmi.pm,v 1.23 2008/03/26 17:20:28 tpederse Exp $
=head1 BUGS
=head1 SEE ALSO
@inproceedings{moore:2004:EMNLP,
author = {Moore, Robert C.},
title = {On Log-Likelihood-Ratios and the Significance of Rare
Events },
booktitle = {Proceedings of EMNLP 2004},
editor = {Dekang Lin and Dekai Wu},
year = 2004,
month = {July},
address = {Barcelona, Spain},
publisher = {Association for Computational Linguistics},
pages = {333--340}
url = L}
L
L
=head1 COPYRIGHT
Copyright (C) 2000-2006, Ted Pedersen, Satanjeev Banerjee, Amruta
Purandare, Bridget Thomson-McInnes and Saiyam Kohli
This program is free software; you can redistribute it and/or modify it
under the terms of the GNU General Public License as published by the Free
Software Foundation; either version 2 of the License, or (at your option)
any later version.
This program is distributed in the hope that it will be useful, but
WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
for more details.
You should have received a copy of the GNU General Public License along
with this program; if not, write to
The Free Software Foundation, Inc.,
59 Temple Place - Suite 330,
Boston, MA 02111-1307, USA.
Note: a copy of the GNU General Public License is available on the web
at L and is included in this
distribution as GPL.txt.
=cut