=head1 NAME
Text::NSP::Measures::3D::MI::pmi - Perl module that implements Pointwise
Mutual Information for trigrams.
=head1 SYNOPSIS
=head3 Basic Usage
use Text::NSP::Measures::3D::MI::pmi;
$pmi_value = calculateStatistic( n111=>10,
n1pp=>40,
np1p=>45,
npp1=>42,
n11p=>20,
n1p1=>23,
np11=>21,
nppp=>100);
if( ($errorCode = getErrorCode()))
{
print STDERR $erroCode." - ".getErrorMessage()."\n";
}
else
{
print getStatisticName."value for bigram is ".$pmi_value."\n";
}
=head1 DESCRIPTION
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:
n1pp * np1p * npp1
m111= --------------------
nppp * nppp
Pointwise Mutual Information (pmi) is defined as the log of the devitation
between the observed frequency of a trigram (n111) and the probability of
that trigram if it were independent (m111).
PMI = log (n111/m111)
=head2 Methods
=over
=cut
package Text::NSP::Measures::3D::MI::pmi;
use Text::NSP::Measures::3D::MI;
use strict;
use Carp;
use warnings;
no warnings 'redefine';
require Exporter;
our ($VERSION, @EXPORT, @ISA, $exp);
$exp=1;
@ISA = qw(Exporter);
@EXPORT = qw(initializeStatistic calculateStatistic
getErrorCode getErrorMessage getStatisticName);
$VERSION = '0.97';
=item initializeStatistic() -Initialization of the pmi_exp parameter if required
INPUT PARAMS : none
RETURN VALUES : none
=cut
sub initializeStatistic
{
$exp = shift;
}
=item calculateStatistic() - This method calculates the pmi value
INPUT PARAMS : $count_values .. Reference of a hash containing
the count values computed by the
count.pl program.
RETURN VALUES : $pmi .. PMI value for this trigram.
=cut
sub calculateStatistic
{
my %values = @_;
# computes and sets 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::3D::MI::getValues(\%values)) ) {
return(0);
}
# Now the calculations!
my $pmi = Text::NSP::Measures::3D::MI::computePMI($n111**$exp, $m111);
return($pmi/log(2));
}
=item getStatisticName() - Returns the name of this statistic
INPUT PARAMS : none
RETURN VALUES : $name .. Name of the measure.
=cut
sub getStatisticName
{
return "Pointwise 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: pmi.pm,v 1.9 2009/11/03 14:53:55 tpederse Exp $
=head1 BUGS
=head1 SEE ALSO
@inproceedings{ church89word,
author = {Kenneth W. Church and Patrick Hanks},
title = {Word association norms, mutual information, and Lexicography},
booktitle = {Proceedings of the 27th. Annual Meeting of the Association for Computational Linguistics},
publisher = {Association for Computational Linguistics},
address = {Vancouver, B.C.},
pages = {76--83},
year = {1989},
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