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Text-NSP-0.91
River stage one • 2 direct dependents • 3 total dependents
++
/ Text::NSP::Measures::2D::MI::pmi

NAME

Text::NSP::Measures::2D::MI::pmi - Perl module that implements Pointwise Mutual Information.

SYNOPSIS

Basic Usage

  use Text::NSP::Measures::2D::MI::pmi;

  my $pmi = Text::NSP::Measures::2D::MI::pmi->new();

  my $npp = 60; my $n1p = 20; my $np1 = 20;  my $n11 = 10;

  $pmi_value = $pmi->calculateStatistic( n11=>$n11,
                                      n1p=>$n1p,
                                      np1=>$np1,
                                      npp=>$npp);

  if( ($errorCode = $pmi->getErrorCode()))
  {
    print STDERR $erroCode." - ".$pmi->getErrorMessage();
  }
  else
  {
    print $pmi->getStatisticName."value for bigram is ".$pmi_value;
  }

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)

Methods

calculateStatistic() - This method calculates the pmi value

INPUT PARAMS : $count_values .. Reference of a hash containing the count valuescomputed 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 1.15 2006/04/20 22:26:19 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 = 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 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.