trueskill/PHPSkills/TrueSkill/FactorGraphTrueSkillCalculator.php

<?php

namespace Moserware\Skills\TrueSkill;

/// <summary>
/// Calculates TrueSkill using a full factor graph.
/// </summary>
class FactorGraphTrueSkillCalculator extends SkillCalculator
{
    public function __construct()
    {
        parent::__construct(SkillCalculatorSupportedOptions::PARTIAL_PLAY | SkillCalculatorSupportedOptions::PARTIAL_UPDATE, TeamsRange::atLeast(2), PlayersRange::atLeast(1));
    }

    public function CalculateNewRatings(GameInfo $gameInfo,
                                        array $teams,
                                        array $teamRanks)
    {
        Guard::argumentNotNull($gameInfo, "gameInfo");
        $this->validateTeamCountAndPlayersCountPerTeam($teams);

        RankSorter::sort($teams, $teamRanks);

        $factorGraph = new TrueSkillFactorGraph($gameInfo, $teams, $teamRanks);
        $factorGraph->buildGraph();
        $factorGraph->runSchedule();

        $probabilityOfOutcome = $factorGraph->getProbabilityOfRanking();

        return $factorGraph->getUpdatedRatings();
    }


    public function calculateMatchQuality(GameInfo $gameInfo,
                                          array $teams)
    {
        // We need to create the A matrix which is the player team assigments.
        $teamAssignmentsList = $teams.ToList();
        $skillsMatrix = $this->getPlayerCovarianceMatrix($teamAssignmentsList);
        $meanVector = $this->getPlayerMeansVector($teamAssignmentsList);
        $meanVectorTranspose = $meanVector->getTranspose();

        $playerTeamAssignmentsMatrix = $this->createPlayerTeamAssignmentMatrix($teamAssignmentsList, $meanVector->getRowCount());
        $playerTeamAssignmentsMatrixTranspose = $playerTeamAssignmentsMatrix->getTranspose();

        $betaSquared = square($gameInfo->getBeta());

        $start = Matrix::multiply($meanVectorTranspose, $playerTeamAssignmentsMatrix);
        $aTa = Matrix::multiply(
                        Matrix::scalarMultiply($betaSquared,
                                               $playerTeamAssignmentsMatrixTranspose),
                        $playerTeamAssignmentsMatrix);

        $aTSA = Matrix::multiply(
                    Matrix::multiply($playerTeamAssignmentsMatrixTranspose, $skillsMatrix),
                    $playerTeamAssignmentsMatrix);

        $middle = Matrix::add($aTa, $aTSA);

        $middleInverse = $middle->getInverse();

        $end = Matrix::multiply($playerTeamAssignmentsMatrixTranspose, $meanVector);

        $expPartMatrix = Matrix::scalarMultiply(-0.5, (Matrix::multiply(Matrix::multiply($start, $middleInverse), $end)));
        $expPart = $expPartMatrix->getDeterminant();

        $sqrtPartNumerator = $aTa->getDeterminant();
        $sqrtPartDenominator = $middle->getDeterminant();
        $sqrtPart = $sqrtPartNumerator / $sqrtPartDenominator;

        $result = exp($expPart) * sqrt($sqrtPart);

        return $result;
    }

    private static function getPlayerMeansVector(array $teamAssignmentsList)
    {
        // A simple vector of all the player means.
        return new Vector($this->getPlayerRatingValues($teamAssignmentsList,
                                                       function($rating) 
                                                       { 
                                                            return $rating->getMean();
                                                       }));
    }

    private static function getPlayerCovarianceMatrix(array $teamAssignmentsList)
    {
        // This is a square matrix whose diagonal values represent the variance (square of standard deviation) of all
        // players.
        return new DiagonalMatrix(
                        $this->getPlayerRatingValues($teamAssignmentsList,
                                                     function($rating)
                                                     {
                                                        return square($rating->getStandardDeviation());
                                                     }));
    }

    // Helper function that gets a list of values for all player ratings
    private static function getPlayerRatingValues(array $teamAssignmentsList,
                                                  $playerRatingFunction)
    {
        $playerRatingValues = array();

        foreach ($teamAssignmentsList as $currentTeam)
        {
            foreach (currentTeam.Values as $currentRating)
            {
                $playerRatingValues[] = $playerRatingFunction($currentRating);
            }
        }

        return $playerRatingValues;
    }

    private static function createPlayerTeamAssignmentMatrix($teamAssignmentsList, $totalPlayers)
    {
        // The team assignment matrix is often referred to as the "A" matrix. It's a matrix whose rows represent the players
        // and the columns represent teams. At Matrix[row, column] represents that player[row] is on team[col]
        // Positive values represent an assignment and a negative value means that we subtract the value of the next
        // team since we're dealing with pairs. This means that this matrix always has teams - 1 columns.
        // The only other tricky thing is that values represent the play percentage.

        // For example, consider a 3 team game where team1 is just player1, team 2 is player 2 and player 3, and
        // team3 is just player 4. Furthermore, player 2 and player 3 on team 2 played 25% and 75% of the time
        // (e.g. partial play), the A matrix would be:

        // A = this 4x2 matrix:
        // |  1.00  0.00 |
        // | -0.25  0.25 |
        // | -0.75  0.75 |
        // |  0.00 -1.00 |

        $playerAssignments = array();
        $totalPreviousPlayers = 0;

        $teamAssignmentsListCount = count($teamAssignmentsList);

        for ($i = 0; $i < $teamAssignmentsListCount - 1; $i++)
        {
            $currentTeam = $teamAssignmentsList[$i];

            // Need to add in 0's for all the previous players, since they're not
            // on this team
            $currentRowValues = array();
            $playerAssignments[] = &$currentRowValues;

            foreach ($currentTeam as $currentRating)
            {
                $currentRowValues[] = PartialPlay::getPartialPlayPercentage($currentRating->getKey());
                // indicates the player is on the team
                $totalPreviousPlayers++;
            }

            $nextTeam = $teamAssignmentsList[$i + 1];
            foreach ($nextTeam as $nextTeamPlayerPair)
            {
                // Add a -1 * playing time to represent the difference
                $currentRowValues[] = -1 * PartialPlay::getPartialPlayPercentage($nextTeamPlayerPair->getKey());
            }
        }

        $playerTeamAssignmentsMatrix = new Matrix($totalPlayers, $teamAssignmentsListCount - 1, $playerAssignments);

        return $playerTeamAssignmentsMatrix;
    }
}

?>