Ted Pedersen


Text::NSP::Measures::2D::MI - Perl module that provides error checks for Loglieklihood, Total Mutual Information, Pointwise Mutual Information and Poisson-Stirling Measure.


Basic Usage

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

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

  $ll_value = $ll->calculateStatistic( n11=>10,

  if( ($errorCode = $ll->getErrorCode()))
    print STDERR $erroCode." - ".$ll->getErrorMessage();
    print $ll->getStatisticName."value for bigram is ".$ll_value;


This module is the base class for the Loglikelihood, Total Mutual Information and the Pointwise Mutual Information measures. All these measure are similar. This module provides error checks specific for these measures, it also implements the computations that are common to these measures.

Log-Likelihood measure is computed as

Log-Likelihood = 2 * [n11 * log(n11/m11) + n12 * log(n12/m12) + n21 * log(n21/m21) + n22 * log(n22/m22)]

Total Mutual Information

TMI = (1/npp)*[n11 * log(n11/m11)/log 2 + n12 * log(n12/m12)/log 2 + n21 * log(n21/m21)/log 2 + n22 * log(n22/m22)/log 2]

Pointwise Mutual Information

PMI = log (n11/m11)/log 2

Poisson Stirling Measures

PS = n11*(log (n11/m11)-1)

All these methods use the ratio of the observed values to expected values, for computations, and thus have common error checks, sothey have been grouped togrther.


calculateStatistic() - This method calls the computeObservedValues() and the computeExpectedValues() methods to compute the observed and expected values. It checks thes values for any errors that might cause the Loglikelihood, TMI & PMI measures to fail.

INPUT PARAMS : $count_values .. Reference of an hash containing the count values computed by the count.pl program.

RETURN VALUES : $observed, $expected .. Observed and expected values for the given counts.

computePMI() - Computes the pmi of a given observed and expected value pair.

INPUT PARAMS : $n ..Observed value $m ..Expected value

RETURN VALUES : log(n/m) ..the log of the ratio of observed value to expected value.


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: MI.pm,v 1.20 2006/06/17 18:03:19 saiyam_kohli Exp $






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.

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    The Free Software Foundation, Inc.,
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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.