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

PHPSkills/TrueSkill/Factors/GaussianPriorFactor.php

@@ -0,0 +1,40 @@
+<?php
+
+namespace Moserware\Skills\TrueSkill\Factors;
+
+/// <summary>
+/// Supplies the factor graph with prior information.
+/// </summary>
+/// <remarks>See the accompanying math paper for more details.</remarks>
+class GaussianPriorFactor extends GaussianFactor
+{
+    private $_newMessage;
+
+    public function __construct($mean, $variance, Variable $variable)
+    {
+        parent::__construct("Prior value going to {0}");
+        $this->_newMessage = new GaussianDistribution($mean, sqrt($variance));
+        $this->createVariableToMessageBinding($variable,
+                                               new Message(
+                                                   GaussianDistribution::fromPrecisionMean(0, 0),
+                                                       "message from {0} to {1}",
+                                                   this, variable));
+    }
+
+    protected function updateMessageVariable(Message $message, Variable $variable)
+    {
+        $oldMarginal = clone $variable->getValue();
+        $oldMessage = $message;
+        $newMarginal =
+            GaussianDistribution::fromPrecisionMean(
+                $oldMarginal->getPrecisionMean() + $this->_newMessage->getPrecisionMean() - $oldMessage->getValue()->getPrecisionMean(),
+                $oldMarginal->getPrecision() + $this->_newMessage->getPrecision() - $oldMessage->getValue()->getPrecision());
+
+        $variable->setValue($newMarginal);
+        $message->setValue($this->_newMessage);
+        return GaussianDistribution::subtract($oldMarginal, $newMarginal);
+    }
+}
+
+
+?>