code: public function det()
      {
          if ($this->m == $this->n) {
              $d = $this->pivsign;
              for ($j = 0; $j < $this->n; ++$j) {
                  $d *= $this->LU[$j][$j];
              }
  
              return $d;
          }
  
          throw new CalculationException(Matrix::MATRIX_DIMENSION_EXCEPTION);
      }
docs: Count determinants.
  
  @return array d matrix deterninat