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Start of factor graph port. Things don't work yet, but a lot of syntax updates towards PHP
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Jeff Moser
216
PHPSkills/TrueSkill/Factors/GaussianWeightedSumFactor.php
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216
PHPSkills/TrueSkill/Factors/GaussianWeightedSumFactor.php
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<?php
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namespace Moserware\Skills\TrueSkill\Factors;
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/// <summary>
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/// Factor that sums together multiple Gaussians.
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/// </summary>
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/// <remarks>See the accompanying math paper for more details.</remarks>
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class GaussianWeightedSumFactor extends GaussianFactor
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{
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private $_variableIndexOrdersForWeights = array();
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// This following is used for convenience, for example, the first entry is [0, 1, 2]
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// corresponding to v[0] = a1*v[1] + a2*v[2]
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private $_weights;
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private $_weightsSquared;
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public function __construct(Variable $sumVariable, array $variablesToSum, array $variableWeights = null)
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{
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parent::__construct($this->createName($sumVariable, $variablesToSum, $variableWeights));
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$this->_weights = array();
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$this->_weightsSquared = array();
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// The first weights are a straightforward copy
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// v_0 = a_1*v_1 + a_2*v_2 + ... + a_n * v_n
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$this->_weights[0] = array();
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$variableWeightsLength = count($variableWeights);
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for($i = 0; $i < $variableWeightsLength; $i++)
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{
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$weight = $variableWeights[$i];
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$this->_weights[0][$i] = $weight;
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$this->_weightsSquared[0][i] = $weight * $weight;
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}
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$variablesToSumLength = count($variablesToSum);
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// 0..n-1
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for($i = 0; $i < ($variablesToSumLength + 1); $i++)
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{
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$this->_variableIndexOrdersForWeights[] = $i;
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}
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// The rest move the variables around and divide out the constant.
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// For example:
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// v_1 = (-a_2 / a_1) * v_2 + (-a3/a1) * v_3 + ... + (1.0 / a_1) * v_0
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// By convention, we'll put the v_0 term at the end
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$weightsLength = $variableWeightsLength + 1;
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for ($weightsIndex = 1; $weightsIndex < $weightsLength; $weightsIndex++)
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{
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$this->_weights[$weightsIndex] = array();
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$variableIndices = array();
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$variableIndices[] = $weightsIndex;
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$currentWeightsSquared = array();
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$this->_WeightsSquared[$weightsIndex] = $currentWeightsSquared;
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// keep a single variable to keep track of where we are in the array.
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// This is helpful since we skip over one of the spots
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$currentDestinationWeightIndex = 0;
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for ($currentWeightSourceIndex = 0;
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$currentWeightSourceIndex < $variableWeights.Length;
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$currentWeightSourceIndex++)
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{
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if ($currentWeightSourceIndex == ($weightsIndex - 1))
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{
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continue;
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}
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$currentWeight = (-$variableWeights[$currentWeightSourceIndex]/$variableWeights[$weightsIndex - 1]);
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if ($variableWeights[$weightsIndex - 1] == 0)
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{
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// HACK: Getting around division by zero
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$currentWeight = 0;
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}
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$currentWeights[$currentDestinationWeightIndex] = $currentWeight;
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$currentWeightsSquared[$currentDestinationWeightIndex] = $currentWeight*currentWeight;
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$variableIndices[$currentDestinationWeightIndex + 1] = $currentWeightSourceIndex + 1;
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$currentDestinationWeightIndex++;
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}
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// And the final one
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$finalWeight = 1.0/$variableWeights[$weightsIndex - 1];
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if ($variableWeights[$weightsIndex - 1] == 0)
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{
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// HACK: Getting around division by zero
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$finalWeight = 0;
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}
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$currentWeights[$currentDestinationWeightIndex] = finalWeight;
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$currentWeightsSquared[currentDestinationWeightIndex] = finalWeight*finalWeight;
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$variableIndices[$variableIndices.Length - 1] = 0;
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$this->_variableIndexOrdersForWeights[] = $variableIndices;
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}
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$this->createVariableToMessageBinding($sumVariable);
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foreach ($variablesToSum as $currentVariable)
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{
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$this->createVariableToMessageBinding($currentVariable);
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}
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}
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public function getLogNormalization()
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{
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$vars = $this->getVariables();
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$messages = $this->getMessages();
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$result = 0.0;
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// We start at 1 since offset 0 has the sum
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$varCount = count($vars);
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for ($i = 1; $i < $varCount; $i++)
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{
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$result += GaussianDistribution::logRatioNormalization($vars[i]->getValue(), $messages[i]->getValue());
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}
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return $result;
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}
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private function updateHelper(array $weights, array $weightsSquared,
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array $messages,
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array $variables)
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{
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// Potentially look at http://mathworld.wolfram.com/NormalSumDistribution.html for clues as
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// to what it's doing
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$messages = $this->getMessages();
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$message0 = clone $messages[0]->getValue();
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$marginal0 = clone $variables[0]->getValue();
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// The math works out so that 1/newPrecision = sum of a_i^2 /marginalsWithoutMessages[i]
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$inverseOfNewPrecisionSum = 0.0;
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$anotherInverseOfNewPrecisionSum = 0.0;
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$weightedMeanSum = 0.0;
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$anotherWeightedMeanSum = 0.0;
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$weightsSquaredLength = count($weightsSquared);
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for ($i = 0; $i < $weightsSquaredLength; $i++)
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{
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// These flow directly from the paper
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$inverseOfNewPrecisionSum += $weightsSquared[i]/
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($variables[$i + 1]->getValue()->getPrecision() - $messages[$i + 1]->getValue()->getPrecision());
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$diff = GaussianDistribution::divide($variables[$i + 1]->getValue(), $messages[$i + 1]->getValue());
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$anotherInverseOfNewPrecisionSum += $weightsSquared[i]/$diff->getPrecision();
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$weightedMeanSum += $weights[i]
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*
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($variables[$i + 1]->getValue()->getPrecisionMean() - $messages[$i + 1]->getValue()->getPrecisionMean())
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/
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($variables[$i + 1]->getValue()->getPrecision() - $messages[$i + 1]->getValue()->getPrecision());
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$anotherWeightedMeanSum += $weights[$i]*$diff->getPrecisionMean()/$diff->getPrecision();
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}
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$newPrecision = 1.0/$inverseOfNewPrecisionSum;
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$anotherNewPrecision = 1.0/$anotherInverseOfNewPrecisionSum;
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$newPrecisionMean = $newPrecision*$weightedMeanSum;
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$anotherNewPrecisionMean = $anotherNewPrecision*$anotherWeightedMeanSum;
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$newMessage = GaussianDistribution::fromPrecisionMean($newPrecisionMean, $newPrecision);
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$oldMarginalWithoutMessage = GaussianDistribution::divide($marginal0, $message0);
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$newMarginal = GaussianDistribution::multiply($oldMarginalWithoutMessage, $newMessage);
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/// Update the message and marginal
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$messages[0]->setValue($newMessage);
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$variables[0]->setValue($newMarginal);
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/// Return the difference in the new marginal
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$finalDiff = GaussianDistribution::subtract($newMarginal, $marginal0);
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return $finalDiff;
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}
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public function updateMessageIndex($messageIndex)
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{
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$allMessages = $this->getMessages();
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$allVariables = $this->getVariables();
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Guard::argumentIsValidIndex($messageIndex, count($allMessages),"messageIndex");
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$updatedMessages = array();
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$updatedVariables = array();
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$indicesToUse = $this->_variableIndexOrdersForWeights[$messageIndex];
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// The tricky part here is that we have to put the messages and variables in the same
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// order as the weights. Thankfully, the weights and messages share the same index numbers,
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// so we just need to make sure they're consistent
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$allMessagesCount = count($allMessages);
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for ($i = 0; i < $allMessagesCount; $i++)
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{
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$updatedMessages[] =$allMessages[$indicesToUse[$i]];
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$updatedVariables[] = $allVariables[$indicesToUse[$i]];
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}
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return updateHelper($this->_weights[$messageIndex],
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$this->_weightsSquared[$messageIndex],
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$updatedMessages,
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$updatedVariables);
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}
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}
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?>
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