=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 $erroCode." - ".getErrorMessage()."\n";
}
else
{
print getStatisticName."value for bigram is ".$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
E<lt>tpederse@d.umn.eduE<gt>
Satanjeev Banerjee, Carnegie Mellon University
E<lt>satanjeev@cmu.eduE<gt>
Amruta Purandare, University of Pittsburgh
E<lt>amruta@cs.pitt.eduE<gt>
Bridget Thomson-McInnes, University of Minnesota Twin Cities
E<lt>bthompson@d.umn.eduE<gt>
Saiyam Kohli, University of Minnesota Duluth
E<lt>kohli003@d.umn.eduE<gt>
=head1 HISTORY
Last updated: $Id: MI.pm,v 1.15 2008/03/26 17:41:33 tpederse Exp $
=head1 BUGS
=head1 SEE ALSO
L<http://groups.yahoo.com/group/ngram/>
L<http://www.d.umn.edu/~tpederse/nsp.html>
=head1 COPYRIGHT
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 L<http://www.gnu.org/licenses/gpl.txt> and is included in this
distribution as GPL.txt.
=cut