public function rowAddScalar(int $mᵢ, $k) : Matrix { if ($mᵢ >= $this->m) { throw new Exception\MatrixException('Row to add does not exist'); } $n = $this->n; $R = $this->A; for ($j = 0; $j < $n; $j++) { $R[$mᵢ][$j] += $k; } return MatrixFactory::create($R); }