=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
<word1><word2> 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 <word1><word2> occur together, and
n12 is the number of times <word1> 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
E<lt>tpederse@d.umn.eduE<gt>
Satanjeev Banerjee, Carnegie Mellon University
E<lt>satanjeev@cmu.eduE<gt>
Amruta Purandare, University of Pittsburgh
E<lt>amruta@cs.pitt.eduE<gt>
Bridget Thomson-McInnes, University of Minnesota Twin Cities
E<lt>bthompson@d.umn.eduE<gt>
Saiyam Kohli, University of Minnesota Duluth
E<lt>kohli003@d.umn.eduE<gt>
=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<http://acl.ldc.upenn.edu/acl2004/emnlp/pdf/Moore.pdf>}
L<http://groups.yahoo.com/group/ngram/>
L<http://www.d.umn.edu/~tpederse/nsp.html>
=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<http://www.gnu.org/licenses/gpl.txt> and is included in this
distribution as GPL.txt.
=cut