NAME

Text::NSP::Measures::3D::MI::pmi - Perl module that implements Pointwise Mutual Information for trigrams.

SYNOPSIS

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";
}``````

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``````

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)``

Methods

initializeStatistic() -Initialization of the pmi_exp parameter if required

INPUT PARAMS : none

RETURN VALUES : none

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.

getStatisticName() - Returns the name of this statistic

INPUT PARAMS : none

RETURN VALUES : \$name .. Name of the measure.

AUTHOR

Ted Pedersen, University of Minnesota Duluth <tpederse@d.umn.edu>

Satanjeev Banerjee, Carnegie Mellon University <satanjeev@cmu.edu>

Amruta Purandare, University of Pittsburgh <amruta@cs.pitt.edu>

Bridget Thomson-McInnes, University of Minnesota Twin Cities <bthompson@d.umn.edu>

Saiyam Kohli, University of Minnesota Duluth <kohli003@d.umn.edu>

HISTORY

Last updated: \$Id: pmi.pm,v 1.8 2006/06/21 11:10:53 saiyam_kohli Exp \$

BUGS

``````  @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},
pages = {76--83},
year = {1989},
url = L<http://acl.ldc.upenn.edu/J/J90/J90-1003.pdf> }``````

http://groups.yahoo.com/group/ngram/

http://www.d.umn.edu/~tpederse/nsp.html

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 http://www.gnu.org/licenses/gpl.txt and is included in this distribution as GPL.txt.