trueskill/src/Numerics/DiagonalMatrix.php

<?php namespace Moserware\Skills\Numerics;

class DiagonalMatrix extends Matrix
{
    public function __construct(array $diagonalValues)
    {
        $diagonalCount = count($diagonalValues);
        $rowCount = $diagonalCount;
        $colCount = $rowCount;

        parent::__construct($rowCount, $colCount);

        for ($currentRow = 0; $currentRow < $rowCount; $currentRow++) {
            for ($currentCol = 0; $currentCol < $colCount; $currentCol++) {
                if ($currentRow == $currentCol) {
                    $this->setValue($currentRow, $currentCol, $diagonalValues[$currentRow]);
                } else {
                    $this->setValue($currentRow, $currentCol, 0);
                }
            }
        }
    }
}