<?php namespace Moserware\Skills\TrueSkill; require_once(dirname(__FILE__) . "/../Numerics/GaussianDistribution.php"); use Moserware\Numerics\GaussianDistribution; final class DrawMargin { public static function getDrawMarginFromDrawProbability($drawProbability, $beta) { // Derived from TrueSkill technical report (MSR-TR-2006-80), page 6 // draw probability = 2 * CDF(margin/(sqrt(n1+n2)*beta)) -1 // implies // // margin = inversecdf((draw probability + 1)/2) * sqrt(n1+n2) * beta // n1 and n2 are the number of players on each team $margin = GaussianDistribution::inverseCumulativeTo(.5*($drawProbability + 1), 0, 1)*sqrt(1 + 1)* $beta; return $margin; } } ?>