=head1 NAME Text::NSP::Measures::3D::MI - Perl module that provides error checks and framework to implement Loglikelihood, Total Mutual Information, Pointwise Mutual Information and Poisson Stirling Measure for trigrams. =head1 SYNOPSIS =head3 Basic Usage use Text::NSP::Measures::3D::MI::ll; $ll_value = calculateStatistic( n111=>10, n1pp=>40, np1p=>45, npp1=>42, n11p=>20, n1p1=>23, np11=>21, nppp=>100); if( ($errorCode = getErrorCode())) { print STDERR $erroCode." - ".getErrorMessage()."\n"; } else { print getStatisticName."value for trigram is ".$ll_value."\n"; } =head1 DESCRIPTION This module is the base class for the Loglikelihood and the True 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. =over =item Log-Likelihood measure is computed as Log-Likelihood = 2 * [n111 * log(n111/m111) + n112 * log(n112/m112) + n121 * log(n121/m121) + n122 * log(n122/m122) + n211 * log(n211/m211) + n212 * log(n212/m212) + n221 * log(n221/m221) + n222 * log(n222/m222)] =item Total Mutual Information tmi = [n111/nppp * log(n111/m111) + n112/nppp * log(n112/m112) + n121/nppp * log(n121/m121) + n122/nppp * log(n122/m122) + n211/nppp * log(n211/m211) + n212/nppp * log(n212/m212) + n221/nppp * log(n221/m221) + n222/nppp * log(n222/m222)] =item Pointwise Mutual Information pmi = log (n111/m111) =item Poisson Stirling Measure ps = n111 * ( log(n111/m111) - 1) =back All these methods use the ratio of the observed values to expected values, for computations, and thus have common error checks, so they have been grouped together. =head2 Methods =over =cut package Text::NSP::Measures::3D::MI; use Text::NSP::Measures::3D; use strict; use Carp; use warnings; # use subs(calculateStatistic); require Exporter; our ($VERSION, @EXPORT, @ISA); @ISA = qw(Exporter); @EXPORT = qw(initializeStatistic calculateStatistic getErrorCode getErrorMessage getStatisticName $n111 $n112 $n121 $n122 $n211 $n212 $n221 $n222 $m111 $m112 $m121 $m122 $m211 $m212 $m221 $m222 $nppp $n1pp $np1p $npp1 $n11p $n1p1 $np11 $n2pp $np2p $npp2 $errorCodeNumber $errorMessage getValues computePMI); $VERSION = '1.03'; =item getValues($count_values) - This method calls computeMarginalTotals the 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 and PMI measures to fail. INPUT PARAMS : $count_values .. Reference of an hash containing the count values computed by the count.pl program. RETURN VALUES : 1/undef ..returns '1' to indicate success and an undefined(NULL) value to indicate failure. =cut sub getValues { my ($values)=@_; if( !(Text::NSP::Measures::3D::computeMarginalTotals($values)) ) { return; } if( !(Text::NSP::Measures::3D::computeObservedValues($values)) ) { return; } if( !(Text::NSP::Measures::3D::computeExpectedValues($values)) ) { return; } # dont want ($nxy / $mxy) to be 0 or less! flag error if so and return; if ( $n111 ) { if ($m111 == 0) { $errorMessage = "Expected value in cell (1,1,1) must not be zero"; $errorCodeNumber = 211; return; } } if ( $n112 ) { if ($m112 == 0) { $errorMessage = "Expected value in cell (1,1,2) must not be zero"; $errorCodeNumber = 211; return; } } if ( $n121 ) { if ($m121 == 0) { $errorMessage = "Expected value in cell (1,2,1) must not be zero"; $errorCodeNumber = 211; return; } } if ( $n122 ) { if ($m122 == 0) { $errorMessage = "Expected value in cell (1,2,2) must not be zero"; $errorCodeNumber = 211; return; } } if ( $n211 ) { if ($m211 == 0) { $errorMessage = "Expected value in cell (2,1,1) must not be zero"; $errorCodeNumber = 211; return; } } if ( $n212 ) { if ($m212 == 0) { $errorMessage = "Expected value in cell (2,1,2) must not be zero"; $errorCodeNumber = 211; return; } } if ( $n221 ) { if ($m221 == 0) { $errorMessage = "Expected value in cell (2,2,1) must not be zero"; $errorCodeNumber = 211; return; } } if ( $n222 ) { if ($m222 == 0) { $errorMessage = "Expected value in cell (2,2,2) must not be zero"; $errorCodeNumber = 211; return; } } if ($m111 < 0) { $errorMessage = "Expected Value for cell(1,1,1) should not be negative"; $errorCodeNumber = 212; return; } if ($m112 < 0) { $errorMessage = "Expected Value for cell (1,1,2) should not be negative"; $errorCodeNumber = 212; return; } if ($m121 < 0) { $errorMessage = "Expected Value for cell (1,2,1) should not be negative"; $errorCodeNumber = 212; return; } if ($m122 < 0) { $errorMessage = "Expected Value for cell (1,2,2) should not be negative"; $errorCodeNumber = 212; return; } if ($m211 < 0) { $errorMessage = "Expected Value for cell (2,1,1) should not be negative"; $errorCodeNumber = 212; return; } if ($m212 < 0) { $errorMessage = "Expected Value for cell (2,1,2) should not be negative"; $errorCodeNumber = 212; return; } if ($m221 < 0) { $errorMessage = "Expected Value for cell (2,2,1) should not be negative"; $errorCodeNumber = 212; return; } if ($m222 < 0) { $errorMessage = "Expected Value for cell (2,2,2) should not be negative"; $errorCodeNumber = 212; return; } # Everything looks good so we can return 1 return 1; } =item computePMI($n, $m) - Computes the pmi of a given observed and expected value pair. INPUT PARAMS : $n ..Observed value $m ..Expected value RETURN VALUES : lognm .. the log of the ratio of observed value to expected value. =cut sub computePMI { my $n = shift; my $m = shift; if($n) { my $val = $n/$m; return log($val); } else { return 0; } } 1; __END__ =back =head1 AUTHOR Ted Pedersen, University of Minnesota Duluth Etpederse@d.umn.eduE Satanjeev Banerjee, Carnegie Mellon University Esatanjeev@cmu.eduE Amruta Purandare, University of Pittsburgh Eamruta@cs.pitt.eduE Bridget Thomson-McInnes, University of Minnesota Twin Cities Ebthomson@d.umn.eduE Saiyam Kohli, University of Minnesota Duluth Ekohli003@d.umn.eduE =head1 HISTORY Last updated: $Id: MI.pm,v 1.16 2011/12/23 22:25:05 btmcinnes Exp $ =head1 BUGS =head1 SEE ALSO L L =head1 COPYRIGHT Copyright (C) 2000-2011, 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 L and is included in this distribution as GPL.txt. =cut