First TwoPlayerTrueSkillCalculator unit test passed

PHPSkills/Elo/GaussianEloCalculator.php

@@ -0,0 +1,26 @@
+<?php
+namespace Moserware\Skills\Elo;
+
+class GaussianEloCalculator extends TwoPlayerEloCalculator
+{
+    // From the paper
+    const STABLE_KFACTOR = 24;
+
+    public function __construct()        
+    {
+        parent::__construct(new KFactor(self::STABLE_KFACTOR));
+    }
+    
+    public function getPlayerWinProbability(GameInfo $gameInfo, $playerRating, $opponentRating)
+    {
+        $ratingDifference = $playerRating - $opponentRating;
+
+        // See equation 1.1 in the TrueSkill paper
+        return GaussianDistribution::cumulativeTo(
+            $ratingDifference
+            /
+            (sqrt(2) * $gameInfo->getBeta()));
+    }
+}
+
+?>