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

  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";
  }

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)

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.

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>

Last updated: $Id: pmi.pm,v 1.9 2009/11/03 14:53:55 tpederse Exp $

  @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 (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.