#!/usr/bin/perl 
use strict; 
use warnings;
use Storable;
use Statistics::Descriptive;

my @grid = @{ retrieve('grid.dat') };
my %param = %{ retrieve('param.dat') }; # range_contx and range_conty parameters

my @contaminated_walks;

for (1 .. 100) {
	my $steps = 100;
	my $num_walks = 100;
	my ($x, $y) = (int(rand $param{range_contx}), int(rand $param{range_conty}));
	my @walks;
	
	for (1 .. $num_walks) {
		my $infected;
		
	 	#Inner loop to perform each step of a random walk  
		for (1 .. $steps) {		  
			my $random_num = rand; 
			my $steps = (1 + int( rand 6 )); 
			if($random_num < 0.25) { 
				$x = ($x - $steps) % $param{range_contx}; 
			} 
			elsif ($random_num < 0.5) { 
				$x = ($x + $steps) % $param{range_contx};
			} 
			elsif ($random_num < 0.75) { 
				$y = ($y - $steps) % $param{range_conty}; 
			} 
			else { 
				$y = ($y + $steps) % $param{range_conty}; 
			}
			
			$infected += $grid[$x][$y] || 0; 
		}
		push @walks, $infected;
	}
	push @contaminated_walks, scalar grep $_, @walks;
}

my $stat = Statistics::Descriptive::Sparse->new();
$stat->add_data(@contaminated_walks);

printf "mean: %.f std. deviation: %.f count: %d\n",
	$stat->mean, $stat->standard_deviation, $stat->count;

__END__
C:\Old_Data\perlp>perl his_stat.pl
mean: 60 std. deviation: 5 count: 100