NAME
Chess::Elo  Perl module to calculate Chess "Elo" ratings
SYNOPSIS
use Chess::Elo qw(:all);
# Alice is going to thump Bob...
my ($alice_elo, $bob_elo) = (2100, 1200);
# Oh no, Alice lost to Bob!
my $result = 0; # 0.5 for draw, 1 for win
my @new_elo_alice_bob = elo ($alice, 0, $bob);
use Data::Dumper; warn Dumper(\@new_elo_alice_bob);
[
'2068.17894295388', # My, Alice took a hit on her rating :)
'1231.82105704612' # Bob is setting pretty
];
DESCRIPTION
This module provides a single function, elo
which allows one to calculate individual ratings based on performance. Typically, a player is given an initial provisional rating of 1600 points. In all cases, one gains and loses points as a function of the playing strength of both parties and the result of their encounter.
The formula used is:
A2 = A1 + 32 ( G  ( 1 / ( 1 + 10 ** ( ( B1 A1) / 400 ) ) ) )
 A2 is Alice's postgame rating
 A1 is Alice rating before the game against Bob
 B1 is Bobs rating before the game against Alice
 G is the game result, in this case:

1, if A beats B 0, if A loses to B 0.5, if A draws to B
METHODS
($new_a, $new_b) = elo($elo_a, $result, $elo_b)
This function takes 3 arguments describing the result of a person with rating $elo_a
competing with the person with rating $elo_b
. The result argument is from the perspective of person A. Thus if A won $result is 1. If A lost, $result is 0. If A drew, $result is 0.5.
EXPORT
None by default, elo
upon request.
SEE ALSO
Christian Bartolomaeus' Elo rating module
Christian's module Games::Ratings provides a number of different rating methods, including the one used by FIDE.
The Perl Chess Mailing List:
Wikipedia discussion on the Elo rating:
http://en.wikipedia.org/wiki/Elo_rating
One part of this discussion deserves repetition:
# 113 players have a rating of 2600 or above. # 16 players have a rating of 2700 or above. # 1 player (Garry Kasparov) has a rating of 2800 or above.
Soccer teams rated by Elo:
AUTHOR
Terrence Brannon, tbone@cpan.org
COPYRIGHT AND LICENSE
Copyright 2003 by Terrence Brannon
This library is free software; you can redistribute it and/or modify it under the same terms as Perl itself.