Algorithm::PageRank - Calculate PageRank in Perl

Algorithm-PageRank documentation Contained in the Algorithm-PageRank distribution.

Index

Code Index:

NAME

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Algorithm::PageRank - Calculate PageRank in Perl

SYNOPSIS

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  use Algorithm::PageRank;
  $pr = new Algorithm::PageRank;

  $pr->graph([
	      0 => 1,
	      0 => 2,
	      1 => 0,
	      2 => 1,
	      ]
	      );

  $pr->iterate();
  $pr->iterate(50);

  $pr->result();

DESCRIPTION

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This is a simple implementation of PageRank algorithm. Please do not expect it to be potent to cope with zilla-size of data.

graph

Feed the graph topology. Vertices count from 0.

iterate

Calculate the pagerank vector. The parameter is the maximal number of iterations. If the vector does not converge before reaching the threshold, then calculation will stop at the maximum. Default iteration number is 100.

You can also reset the dampening factor ($Algorithm::PageRank::d_factor). The default value is 0.05.

result

Return the pagerank vector in PDL object format.

COPYRIGHT

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Copyright (C) 2004 by Yung-chung Lin (a.k.a. xern) <xern@cpan.org>

This package is free software; you can redistribute it and/or modify it under the same terms as Perl itself

Algorithm-PageRank documentation Contained in the Algorithm-PageRank distribution. 
package Algorithm::PageRank;
$|++;
use strict;
use warnings;
our $VERSION = '0.08';

use fields qw(graph prvect size);

sub new { bless {}, shift }

use List::Util;
use PDL;
#use Data::Dumper;
#use PDL::IO::Dumper;

#*STDERR = \*STDOUT;

our $d_factor = 0.05; # dampening factor

sub graph {
    my $self = shift;
    my $graph = shift;

    die "Odd number of node numbers is not valid\n" if scalar(@$graph)%2;

    my $size = List::Util::max(@$graph)+1;
    $self->{size} = $size;

    $self->{graph} = zeroes($size, $size);
    for (my $i = 0 ; $i<@$graph ; $i+=2){
	$self->{graph}->index2d(
				$graph->[$i],
				$graph->[$i+1],
				) .= 1;
    }

    foreach my $i (0..$self->{size}-1){
	my $outdeg_sum = sum $self->{graph}->slice(join q/:/, $i, $i); 
	if($outdeg_sum){
	    $self->{graph}->slice(join q/:/, $i, $i) /=
		$outdeg_sum;
	}
    }

    $self->{graph} = transpose $self->{graph};
    $self->{prvect} = ones($size) / $size;    # the initial pagerank
#    print $self->{graph}->slice(":");
#    print sdump $self;
#    print $self->{prvect}->slice(":");
}

sub iterate {
    my $self = shift;
    my $iter = shift || 100;
    my $normal_factor = $d_factor/$self->{size};
    my $inv_d_factor = 1 - $d_factor;
#    print $self->{prvect}->slice(":");
#    print $self->{graph}->slice(":");
    foreach (1..$iter){
      $self->{prvect} =
	$inv_d_factor * $self->{prvect} x $self->{graph} + $normal_factor * $self->{prvect};
#      print $self->{prvect}->slice(":");
#      print sdump (($d_factor/$self->{size}) * $self->{prvect});
    }
}


sub result {
    my $self = shift;
    $self->{prvect};
}

1;
__END__
# Below is stub documentation for your module. You better edit it!