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Text::NSP::Measures::2D::MI::pmi.3pm
Langue: en
Version: 2006-06-21 (mandriva - 01/05/08)
Section: 3 (Bibliothèques de fonctions)
NAME
Text::NSP::Measures::2D::MI::pmi - Perl module that implements PointwiseMutual Information.
SYNOPSIS
Basic Usageuse Text::NSP::Measures::2D::MI::pmi;
my $npp = 60; my $n1p = 20; my $np1 = 20; my $n11 = 10;
$pmi_value = calculateStatistic( n11=>$n11, n1p=>$n1p, np1=>$np1, npp=>$npp);
if( ($errorCode = getErrorCode())) { print STDERR $errorCode." - ".getErrorMessage()."\n""; } else { print getStatisticName."value for bigram is ".$pmi_value."\n""; }
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
Pointwise Mutual Information (pmi) is defined as the log of the devitation between the observed frequency of a bigram (n11) and the probability of that bigram if it were independent (m11).
PMI = log (n11/m11)
The Pointwise Mutual Information tends to overestimate bigrams with low observed frequency counts. To prevent this sometimes a variation of pmi is used which increases the influence of the observed frequency.
PMI = log((n11^$exp)/m11)
The $exp is 1 by default, so by default the measure will compute the Pointwise Mutual Information for the given bigram. To use a variation of the measure, users can pass the $exp parameter using the --pmi_exp command line option in statistic.pl or by passing the $exp to the initializeStatistic() method from their program.
The usage for statistic.pl is
statistic.pl pmi out_pmi.stt out.cnt - for Point Wise Mutual Information $exp is 1 in this case.
statistic.pl --pmi_exp 2 pmi out_pmi2.stt out.cnt - for the variant with $exp set to 2.
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 bigram.
- 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 1.23 2006/06/21 11:10:52 saiyam_kohli Exp $BUGS
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<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
Copyright (C) 2000-2006, Ted Pedersen, Satanjeev Banerjee, Amruta Purandare, Bridget Thomson-McInnes and Saiyam KohliThis 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.
Contenus ©2006-2024 Benjamin Poulain
Design ©2006-2024 Maxime Vantorre