-our $q = log(10)/400.0;
-our $pi = 3.1415926535897932384626433832795;
-
-# computes a^b
-sub pow {
- my ($a, $b) = @_;
-
- # a^b = exp(log(a^b)) = exp(b log a)
- return exp($b * log($a));
-}
-
-sub g {
- my $rd = shift;
- return 1.0 / sqrt(1.0 + 3.0 * $q * $q * $rd * $rd / ($pi*$pi));
-}
-
-sub E {
- my ($r, $rating, $rd) = @_;
- return 1.0 / (1.0 + pow(10.0, - g($rd) * ($r - $rating) / 400.0));
-}
-
-sub dsq {
- my ($r, $rating, $rd) = @_;
- return 1.0 / ($q*$q * g($rd) * g($rd) * E($r, $rating, $rd) * (1 - E($r, $rating, $rd)));
-}
-