public function norm1()
    {
        $r = 0;
 
        for ($j = 0; $j < $this->n; $j++) {
            $s = 0;
 
            for ($i = 0; $i < $this->m; $i++) {
                $s += abs($this->A[$i][$j]);
            }
 
            $r = ($r > $s) ? $r : $s;
        }
 
        return $r;
    }