Naming tweak

Skills/TrueSkill/DrawMargin.php

@@ -0,0 +1,26 @@
+<?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;
+    }
+}
+
+?>