# NAME

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

# SYNOPSIS

### Basic Usage

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

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

\$ll_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 ".\$ll_value."\n"";
}``````

# DESCRIPTION

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.

## Methods

getValues() - This method calls the computeMarginalTotals(), computeObservedValues() and the computeExpectedValues() methods to compute the observed and expected values. It checks these 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 : 1/undef ..returns '1' to indicate success and an undefined(NULL) value to indicate faliure.

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.

# 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: MI.pm,v 1.26 2006/09/15 23:27:03 saiyam_kohli Exp \$

# BUGS

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.