public static function zeros(int $m, int $n) : self
    {
        if ($m < 1 or $n < 1) {
            throw new InvalidArgumentException('Dimensionality must be'
                . ' greater than 0 on all axes.');
        }

        $a = array_fill(0, $m, array_fill(0, $n, 0));

        return self::quick($a);
    }