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 * 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 1.9 2009/11/03 14:53:55 tpederse Exp $

BUGS

COPYRIGHT

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.