trueskill/Skills/Elo/FideEloCalculator.php

<?php

namespace Moserware\Skills\Elo;

require_once(dirname(__FILE__) . "/FideKFactor.php");
require_once(dirname(__FILE__) . "/TwoPlayerEloCalculator.php");

/** Including Elo's scheme as a simple comparison.
 *  See http://en.wikipedia.org/wiki/Elo_rating_system#Theory
 *  for more details
 */
class FideEloCalculator extends TwoPlayerEloCalculator
{
    public function __construct(FideKFactor $kFactor)        
    {
        parent::__construct($kFactor);
    }

    public static function createWithDefaultKFactor()
    {
        return new FideEloCalculator(new FideKFactor());
    }

    public static function createWithProvisionalKFactor()
    {
        return new FideEloCalculator(new ProvisionalFideKFactor());
    }

    public function getPlayerWinProbability($gameInfo, $playerRating, $opponentRating)
    {
        $ratingDifference = $opponentRating - $playerRating;

        return 1.0
               /
               (
                   1.0 + pow(10.0, $ratingDifference / (2 * $gameInfo->getBeta()))
               );
    }        
}

?>