#!/usr/bin/perl -w

use strict;
use Math::Gsl::Sf qw(gamma gamma_e);
my $r = new Math::Gsl::Sf::Result;


for (1 .. 25 ){
	gamma_e( $_ , $r );
	print "Difference ($_):" .  abs( $r->val - fact($_- 1) )  . " vs ";
	print $r->err . "\n";
}

sub fact {
	my $x = shift;
	return 1 if $x == 0;
	return $x * fact( $x - 1 );
}