You could get more accuracy from the Math::Pari version if you did the powers and multiplies on the Pari side and didn't use logs: 
sub binomial_pari {
   my ($k, $n, $p) = @_;
   my $first = binomial($n,$k);
   # gpui is imported from Math::Pari.  It is x ** y.
   my $second = gpui($p,$k);
   my $third = gpui(1.0 - $p, $n - $k);
   my $Prob = $first * $second * $third;
   return $Prob;
}

[download]
Here are the different results I get: 
Sub Binom Comb       = 0.3125
Sub Binom Log        = 0.3125000000000001128
Sub Binom Pari       = 0.3125000000000000000

[download]

In reply to Re: Getting Binomial Distribution under Math::Pari (log) and Combinatorial Method by tall_man
in thread Getting Binomial Distribution under Math::Pari (log) and Combinatorial Method by monkfan

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