Start of factor graph port. Things don't work yet, but a lot of syntax updates towards PHP

PHPSkills/TrueSkill/Factors/GaussianLikelihoodFactor.php

@@ -0,0 +1,78 @@
+<?php
+
+namespace Moserware\Skills\TrueSkill\Factors;
+
+/// <summary>
+/// Connects two variables and adds uncertainty.
+/// </summary>
+/// <remarks>See the accompanying math paper for more details.</remarks>
+class GaussianLikelihoodFactor extends GaussianFactor
+{
+    private $_precision;
+
+    public function __construct($betaSquared, Variable $variable1, Variable $variable2)
+    {
+        parent::__construct("Likelihood of {0} going to {1}");
+        $this->_precision = 1.0/$betaSquared;
+        $this->createVariableToMessageBinding($variable1);
+        $this->createVariableToMessageBinding($variable2);
+    }
+
+    public function getLogNormalization()
+    {
+        $vars = $this->getVariables();
+        $messages = $this->getMessages();
+
+        return GaussianDistribution::logRatioNormalization(
+                $vars[0]->getValue(),
+                $messages[0]->getValue());
+    }
+
+    private function updateHelper(Message $message1, Message $message2,
+                                  Variable $variable1, Variable $variable2)
+    {
+        $message1Value = clone $message1->getValue();
+        $message2Value = clone $message2->getValue();
+
+        $marginal1 = clone $variable1->getValue();
+        $marginal2 = clone $variable2->getValue();
+
+        $a = $this->_precision/($this->_precision + $marginal2->getPrecision() - $message2Value->getPrecision());
+
+        $newMessage = GaussianDistribution::fromPrecisionMean(
+            $a*($marginal2->getPrecisionMean() - $message2Value->getPrecisionMean()),
+            $a*($marginal2->getPrecision() - $message2Value->getPrecision()));
+
+        $oldMarginalWithoutMessage = GaussianDistribution::divide($marginal1, $message1Value);
+
+        $newMarginal = GaussianDistribution::multiply($oldMarginalWithoutMessage, $newMessage);
+
+        /// Update the message and marginal
+
+        $message1->setValue($newMessage);
+        $variable1->setValue($newMarginal);
+
+        /// Return the difference in the new marginal
+        return GaussianDistribution::subtract($newMarginal, $marginal1);
+    }
+
+    public function updateMessageIndex($messageIndex)
+    {
+        $messages = $this->getMessages();
+        $vars = $this->getVariables();
+
+        switch ($messageIndex)
+        {
+            case 0:
+                return $this->updateHelper($messages[0], $messages[1],
+                                           $vars[0], $vars[1]);
+            case 1:
+                return $this->updateHelper($messages[1], $messages[0],
+                                           $vars[1], $vars[0]);
+            default:
+                throw new Exception();
+        }
+    }
+}
+
+?>