elseif(strtoupper($pattern) == "D"){
    for ($row = 0; $row < $size; $row++)
        $matrix[$row][0] = $currentNumber++;
    for ($col = 1; $col < $size; $col++)
        $matrix[$size - 1][$col] = $currentNumber++;
    for ($row = $size - 2; $row >= 0; $row--)
        $matrix[$row][$size - 1] = $currentNumber++;
    for ($col = $size - 2; $col >= 1; $col--)
        $matrix[0][$col] = $currentNumber++;
    for ($col = 1; $col < $size - 1; $col++)
        for ($row = 1; $row < $size - 1; $row++)
            $matrix[$row][$col] = $currentNumber++;
}