Games::Ratings::Chess::FIDE - calculate changes to FIDE ratings (Elos)

Games-Ratings documentation Contained in the Games-Ratings distribution.

Index

Code Index:

NAME

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Games::Ratings::Chess::FIDE - calculate changes to FIDE ratings (Elos)

VERSION

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This document describes Games::Ratings::Chess::FIDE version 0.0.4

SYNOPSIS

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 use Games::Ratings::Chess::FIDE;

 my $player = Games::Ratings::Chess::FIDE->new();
 $player->set_rating(2240);
 $player->set_coefficient(15);
 $player->add_game( {
                      opponent_rating => 2114,
                      result          => 'win',   ## or 'draw' or 'loss'
                    }
                  );

 my $rating_change = sprintf( "%+.2f", $player->get_rating_change() );
 my $new_rating = $player->get_new_rating();

DESCRIPTION

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This module provides methods to calculate FIDE rating (Elo) changes for one player, having played one or more rated games. Gains and losses are calculated according to the FIDE rating rules (cmp. FIDE Rating Regulations, FIDE Handbook B.02.10: http://www.fide.com/info/handbook?id=75&view=article).

FIDE uses a table with scoring probabilities in dependence from rating differences between the players.

FIDE does _not_ use the formula P = 1/(1 + 10 ^ [D/400]).

Furthermore FIDE uses a development coefficient (K) depending on the current rating and the number of rated games. * K = 25 for a player with a total of less than 30 games. * K = 15 as long as a player`s rating remains under 2400. * K = 10 once a player`s published rating has reached 2400

INTERFACE

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This modules provides the following methods specific to FIDE ratings. Other (more generic) methods for rating calculation are provided by Games::Ratings. Please check the documentation of Games::Ratings for those methods.

get_rating_change

  my $rating_change = sprintf("%+.2f", $player->get_rating_change() );

Calculate rating changes for all stored games and return sum of those changes.

get_new_rating

  my $new_rating = $player->get_new_rating();

Calculate new rating after the given games.

get_points_expected

  my $points_expected = $player->get_points_expected();

Calculate expected points according to rating differences between own rating and opponents ratings.

get_performance

  my $performance = $player->get_performance();

Calculate performance according to average rating of opponents and percentage score.

CONFIGURATION AND ENVIRONMENT

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Games::Ratings requires no configuration files or environment variables.

DEPENDENCIES

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This module relies on Games::Ratings which provides some generic methods, e.g. * new() * get_rating() * set_rating() * get_coefficient() * set_coefficient() * add_game() * remove_all_games() * DESTROY()

DIAGNOSTICS

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At the moment, there are no error or warning messages that the module can generate.

Error message here, perhaps with %s placeholders

[Description of error here]

Another error message here

[Description of error here]

[Et cetera, et cetera]

INCOMPATIBILITIES

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None reported.

BUGS AND LIMITATIONS

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No bugs have been reported.

At the moment, it's not possible to compute a FIDE rating for a previously unrated player.

Note, that a missing development coefficient (set via $player->set_coefficient()) may lead to incorrect results. The program tries to guess the correct factor according to the players rating, but it will err for players new to the rating list with less than thirty games played.

Please report any bugs or feature requests to bug-games-ratings@rt.cpan.org, or through the web interface at http://rt.cpan.org.

AUTHOR

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Christian Bartolomaeus <bartolin@gmx.de>

ACKNOWLEDGMENTS

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This module was inspired by Terrence Brannon's module Chess::Elo (http://search.cpan.org/~tbone/Chess-Elo/).

SEE ALSO

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http://en.wikipedia.org/wiki/Elo_rating for informations about the Elo system.

http://www.fide.com/info/handbook?id=11&view=category for informations about the FIDE rating system (esp. point 10.0).

LICENCE AND COPYRIGHT

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Copyright (c) 2010, Christian Bartolomaeus <bartolin@gmx.de>. All rights reserved.

This module is free software; you can redistribute it and/or modify it under the same terms as Perl itself. See perlartistic.

DISCLAIMER OF WARRANTY

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BECAUSE THIS SOFTWARE IS LICENSED FREE OF CHARGE, THERE IS NO WARRANTY FOR THE SOFTWARE, TO THE EXTENT PERMITTED BY APPLICABLE LAW. EXCEPT WHEN OTHERWISE STATED IN WRITING THE COPYRIGHT HOLDERS AND/OR OTHER PARTIES PROVIDE THE SOFTWARE "AS IS" WITHOUT WARRANTY OF ANY KIND, EITHER EXPRESSED OR IMPLIED, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. THE ENTIRE RISK AS TO THE QUALITY AND PERFORMANCE OF THE SOFTWARE IS WITH YOU. SHOULD THE SOFTWARE PROVE DEFECTIVE, YOU ASSUME THE COST OF ALL NECESSARY SERVICING, REPAIR, OR CORRECTION.

IN NO EVENT UNLESS REQUIRED BY APPLICABLE LAW OR AGREED TO IN WRITING WILL ANY COPYRIGHT HOLDER, OR ANY OTHER PARTY WHO MAY MODIFY AND/OR REDISTRIBUTE THE SOFTWARE AS PERMITTED BY THE ABOVE LICENCE, BE LIABLE TO YOU FOR DAMAGES, INCLUDING ANY GENERAL, SPECIAL, INCIDENTAL, OR CONSEQUENTIAL DAMAGES ARISING OUT OF THE USE OR INABILITY TO USE THE SOFTWARE (INCLUDING BUT NOT LIMITED TO LOSS OF DATA OR DATA BEING RENDERED INACCURATE OR LOSSES SUSTAINED BY YOU OR THIRD PARTIES OR A FAILURE OF THE SOFTWARE TO OPERATE WITH ANY OTHER SOFTWARE), EVEN IF SUCH HOLDER OR OTHER PARTY HAS BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGES.

Games-Ratings documentation Contained in the Games-Ratings distribution. 
package Games::Ratings::Chess::FIDE;

## TODO: check arguments for subroutines (use Data::Checker)?
## TODO: Error handling
##       * croak()
##       * perldoc anpassen

use strict;
use warnings;
use Carp;

use 5.6.1;               # 'our' was introduced in perl 5.6
use version; our $VERSION = qv('0.0.5');

## look in Games::Ratings for methods not provide by this package
use base qw ( Games::Ratings );

## calculate rating change
sub get_rating_change {
    my ($self) = @_;

    ## get own rating and own coefficient
    my $own_rating      = $self->get_rating();
    my $own_coefficient = $self->get_coefficient();

    my $rating_change_total;
    ## calculate rating change for each game separately
    foreach my $game_ref ( $self->get_all_games() ) {
        ## add rating change for single game to total rating change
        $rating_change_total += _calc_rating_change_for_single_game(
                                    $own_rating,
                                    $own_coefficient,
                                    $game_ref->{opponent_rating},
                                    $game_ref->{result},
                                );
    }

    ## return total rating change
    return $rating_change_total;
}

## calculate new rating
sub get_new_rating {
    my ($self) = @_;

    ## $R_o -- old rating
    my $R_o = $self->get_rating();

    ## $R_n -- new rating (rounded)
    my $R_n = sprintf( "%.f", $R_o + $self->get_rating_change() );

    ## return new rating
    return $R_n;
}

## calculate expected points
sub get_points_expected {
    my ($self) = @_;
    
    ## $W_e -- expected points
    my $W_e;

    ## $own_rating -- own rating
    my $own_rating = $self->get_rating();

    ## sum up expected points for all games
    foreach my $game_ref ( $self->get_all_games() ) {
        $W_e += _get_scoring_probability_for_single_game(
                    $own_rating,
                    $game_ref->{opponent_rating},
                );
    }

    ## return expected points
    return $W_e;
}

## calculate performance
sub get_performance {
    my ($self) = @_;

    ## $R_h -- performance (independent from old rating)
    my $R_h;

    ## average rating of opponents
    my $R_c = $self->get_average_rating_of_opponents();

    ## $P -- percentage score (two digits needed)
    my $P = sprintf( "%.2f", $self->get_percentage_score() );

    ## if player scored 100 % or 0 % it's not possible to calc. performance
    if ($P == 1) {
        $R_h = $R_c + 667;
        return $R_h;
    }
    if ($P == 0) {
        $R_h = $R_c - 667;
        return $R_h;
    }

    ## lookup $D rating difference according to $P from probability table 
    my $D = _get_rating_difference_matching_percentage_score($P);

    ## calculate performance
    $R_h = $R_c + $D;

    ## return performance
    return $R_h;
}

########################
## internal functions ##
########################

## scoring probabilities depending from rating difference (FIDE B0210.1b)
our %scoring_probability_lookup_table;
_set_scoring_probability_lookup_table();

## lookup table needed to determine performance (FIDE B0210.1a)
our %reverse_scoring_probability_lookup_table;
_set_reverse_scoring_probability_lookup_table();

## calculate rating change for single game
sub _calc_rating_change_for_single_game {
    my ($A_rating, $A_coefficient, $B_rating, $result) = @_;
  
    ## get numerical result ( win=>1 draw=>0.5 loss=>0 )
    my $numerical_result = Games::Ratings::_get_numerical_result($result);

    ## check whether development coefficient is provided -- guess otherwise
    if (! defined $A_coefficient) {
        $A_coefficient = _guess_coefficient($A_rating);
    }

    ## get scoring probability for player A
    my $A_exp = _get_scoring_probability_for_single_game($A_rating,$B_rating);

    ## compute rating changes for player A
    my $A_rating_change = $A_coefficient * ($numerical_result-$A_exp);
  
    ## return rating changes for player A
    return ($A_rating_change);
}

## try to guess development coefficient
sub _guess_coefficient {
    my ($player_rating) = @_;

    ## guess coefficient according to rating (cmp. FIDE handbook B0210.52)
    my $player_coefficient;
    if ($player_rating >= 2400) {
        $player_coefficient = 10;
    }
    else {
        $player_coefficient = 15;
    }

    ## return guessed coefficient
    return $player_coefficient;
}

## calculate scoring probability for a single game
sub _get_scoring_probability_for_single_game {
    my ($A_rating,$B_rating) = @_;

    my $rating_difference = _get_rating_difference($A_rating,$B_rating);

    ## get scoring probability of player A from lookup table 
    my $A_exp;
    if ($rating_difference >= 0) {
        $A_exp = $scoring_probability_lookup_table{$rating_difference};
    }
    else {
        $A_exp = 1 - $scoring_probability_lookup_table{0-$rating_difference};
    }

    ## return scoring probability for player A
    return ($A_exp);
}

## calculate rating difference which is used to calc the scoring probability
sub _get_rating_difference {
    my ($A, $B) = @_;

    ## compute real rating difference
    my $rating_difference = ( $A-$B );

    ## large rating differences are cut (FIDE handbook B0210.51, 2nd sentence)
    if ($rating_difference > '350') {
        $rating_difference = '350';
    }
    if ($rating_difference < '-350') {
        $rating_difference = '-350';
    }

    ## return rating difference used for rating calculations
    return $rating_difference;
}

## calculate rating differences matching percentage score
sub _get_rating_difference_matching_percentage_score {
    my ($P) = @_;

    ## lookup $D (rating difference) from lookup table
    my $D;
    if ($P lt 0.5) {
        ## percentage score negated -- so we can use our lookup table
        my $P_negated = sprintf("%.2f", 1-$P);
        $D = -($reverse_scoring_probability_lookup_table{$P_negated});
    }
    else {
        $D = $reverse_scoring_probability_lookup_table{$P};
    }

    ## return $D
    return $D;
}

## use hash as lookup table for scoring probability (cmp. FIDE B0210.1b)
sub _set_scoring_probability_lookup_table {
    foreach my $rating_difference (0..3) {
        $scoring_probability_lookup_table{$rating_difference} = 0.50;
    }
    foreach my $rating_difference (4..10) {
        $scoring_probability_lookup_table{$rating_difference} = 0.51;
    }
    foreach my $rating_difference (11..17) {
        $scoring_probability_lookup_table{$rating_difference} = 0.52;
    }
    foreach my $rating_difference (18..25) {
        $scoring_probability_lookup_table{$rating_difference} = 0.53;
    }
    foreach my $rating_difference (26..32) {
        $scoring_probability_lookup_table{$rating_difference} = 0.54;
    }
    foreach my $rating_difference (33..39) {
        $scoring_probability_lookup_table{$rating_difference} = 0.55;
    }
    foreach my $rating_difference (40..46) {
        $scoring_probability_lookup_table{$rating_difference} = 0.56;
    }
    foreach my $rating_difference (47..53) {
        $scoring_probability_lookup_table{$rating_difference} = 0.57;
    }
    foreach my $rating_difference (54..61) {
        $scoring_probability_lookup_table{$rating_difference} = 0.58;
    }
    foreach my $rating_difference (62..68) {
        $scoring_probability_lookup_table{$rating_difference} = 0.59;
    }
    foreach my $rating_difference (69..76) {
        $scoring_probability_lookup_table{$rating_difference} = 0.60;
    }
    foreach my $rating_difference (77..83) {
        $scoring_probability_lookup_table{$rating_difference} = 0.61;
    }
    foreach my $rating_difference (84..91) {
        $scoring_probability_lookup_table{$rating_difference} = 0.62;
    }
    foreach my $rating_difference (92..98) {
        $scoring_probability_lookup_table{$rating_difference} = 0.63;
    }
    foreach my $rating_difference (99..106) {
        $scoring_probability_lookup_table{$rating_difference} = 0.64;
    }
    foreach my $rating_difference (107..113) {
        $scoring_probability_lookup_table{$rating_difference} = 0.65;
    }
    foreach my $rating_difference (114..121) {
        $scoring_probability_lookup_table{$rating_difference} = 0.66;
    }
    foreach my $rating_difference (122..129) {
        $scoring_probability_lookup_table{$rating_difference} = 0.67;
    }
    foreach my $rating_difference (130..137) {
        $scoring_probability_lookup_table{$rating_difference} = 0.68;
    }
    foreach my $rating_difference (138..145) {
        $scoring_probability_lookup_table{$rating_difference} = 0.69;
    }
    foreach my $rating_difference (146..153) {
        $scoring_probability_lookup_table{$rating_difference} = 0.70;
    }
    foreach my $rating_difference (154..162) {
        $scoring_probability_lookup_table{$rating_difference} = 0.71;
    }
    foreach my $rating_difference (163..170) {
        $scoring_probability_lookup_table{$rating_difference} = 0.72;
    }
    foreach my $rating_difference (171..179) {
        $scoring_probability_lookup_table{$rating_difference} = 0.73;
    }
    foreach my $rating_difference (180..188) {
        $scoring_probability_lookup_table{$rating_difference} = 0.74;
    }
    foreach my $rating_difference (189..197) {
        $scoring_probability_lookup_table{$rating_difference} = 0.75;
    }
    foreach my $rating_difference (198..206) {
        $scoring_probability_lookup_table{$rating_difference} = 0.76;
    }
    foreach my $rating_difference (207..215) {
        $scoring_probability_lookup_table{$rating_difference} = 0.77;
    }
    foreach my $rating_difference (216..225) {
        $scoring_probability_lookup_table{$rating_difference} = 0.78;
    }
    foreach my $rating_difference (226..235) {
        $scoring_probability_lookup_table{$rating_difference} = 0.79;
    }
    foreach my $rating_difference (236..245) {
        $scoring_probability_lookup_table{$rating_difference} = 0.80;
    }
    foreach my $rating_difference (246..256) {
        $scoring_probability_lookup_table{$rating_difference} = 0.81;
    }
    foreach my $rating_difference (257..267) {
        $scoring_probability_lookup_table{$rating_difference} = 0.82;
    }
    foreach my $rating_difference (268..278) {
        $scoring_probability_lookup_table{$rating_difference} = 0.83;
    }
    foreach my $rating_difference (279..290) {
        $scoring_probability_lookup_table{$rating_difference} = 0.84;
    }
    foreach my $rating_difference (291..302) {
        $scoring_probability_lookup_table{$rating_difference} = 0.85;
    }
    foreach my $rating_difference (303..315) {
        $scoring_probability_lookup_table{$rating_difference} = 0.86;
    }
    foreach my $rating_difference (316..328) {
        $scoring_probability_lookup_table{$rating_difference} = 0.87;
    }
    foreach my $rating_difference (329..344) {
        $scoring_probability_lookup_table{$rating_difference} = 0.88;
    }
    foreach my $rating_difference (345..350) {
        $scoring_probability_lookup_table{$rating_difference} = 0.89;
    }
}

## use hash as lookup table (rating differences given a percentage score)
## (cmp. FIDE B0210.1a)
sub _set_reverse_scoring_probability_lookup_table {
    $reverse_scoring_probability_lookup_table{'0.50'} = '0';
    $reverse_scoring_probability_lookup_table{'0.51'} = '7';
    $reverse_scoring_probability_lookup_table{'0.52'} = '14';
    $reverse_scoring_probability_lookup_table{'0.53'} = '21';
    $reverse_scoring_probability_lookup_table{'0.54'} = '29';
    $reverse_scoring_probability_lookup_table{'0.55'} = '36';
    $reverse_scoring_probability_lookup_table{'0.56'} = '43';
    $reverse_scoring_probability_lookup_table{'0.57'} = '50';
    $reverse_scoring_probability_lookup_table{'0.58'} = '57';
    $reverse_scoring_probability_lookup_table{'0.59'} = '65';
    $reverse_scoring_probability_lookup_table{'0.60'} = '72';
    $reverse_scoring_probability_lookup_table{'0.61'} = '80';
    $reverse_scoring_probability_lookup_table{'0.62'} = '87';
    $reverse_scoring_probability_lookup_table{'0.63'} = '95';
    $reverse_scoring_probability_lookup_table{'0.64'} = '102';
    $reverse_scoring_probability_lookup_table{'0.65'} = '110';
    $reverse_scoring_probability_lookup_table{'0.66'} = '117';
    $reverse_scoring_probability_lookup_table{'0.67'} = '125';
    $reverse_scoring_probability_lookup_table{'0.68'} = '133';
    $reverse_scoring_probability_lookup_table{'0.69'} = '141';
    $reverse_scoring_probability_lookup_table{'0.70'} = '149';
    $reverse_scoring_probability_lookup_table{'0.71'} = '158';
    $reverse_scoring_probability_lookup_table{'0.72'} = '166';
    $reverse_scoring_probability_lookup_table{'0.73'} = '175';
    $reverse_scoring_probability_lookup_table{'0.74'} = '184';
    $reverse_scoring_probability_lookup_table{'0.75'} = '193';
    $reverse_scoring_probability_lookup_table{'0.76'} = '202';
    $reverse_scoring_probability_lookup_table{'0.77'} = '211';
    $reverse_scoring_probability_lookup_table{'0.78'} = '220';
    $reverse_scoring_probability_lookup_table{'0.79'} = '230';
    $reverse_scoring_probability_lookup_table{'0.80'} = '240';
    $reverse_scoring_probability_lookup_table{'0.81'} = '251';
    $reverse_scoring_probability_lookup_table{'0.82'} = '262';
    $reverse_scoring_probability_lookup_table{'0.83'} = '273';
    $reverse_scoring_probability_lookup_table{'0.84'} = '284';
    $reverse_scoring_probability_lookup_table{'0.85'} = '296';
    $reverse_scoring_probability_lookup_table{'0.86'} = '309';
    $reverse_scoring_probability_lookup_table{'0.87'} = '322';
    $reverse_scoring_probability_lookup_table{'0.88'} = '336';
    $reverse_scoring_probability_lookup_table{'0.89'} = '351';
    $reverse_scoring_probability_lookup_table{'0.90'} = '366';
    $reverse_scoring_probability_lookup_table{'0.91'} = '383';
    $reverse_scoring_probability_lookup_table{'0.92'} = '401';
    $reverse_scoring_probability_lookup_table{'0.93'} = '422';
    $reverse_scoring_probability_lookup_table{'0.94'} = '444';
    $reverse_scoring_probability_lookup_table{'0.95'} = '470';
    $reverse_scoring_probability_lookup_table{'0.96'} = '501';
    $reverse_scoring_probability_lookup_table{'0.97'} = '538';
    $reverse_scoring_probability_lookup_table{'0.98'} = '589';
    $reverse_scoring_probability_lookup_table{'0.99'} = '677';
}


1; # Magic true value required at end of module
__END__