docs: public double permutationDeterminant()
      {
          int sign = 1;
          double sum = 0;
          PermutationMatrix pm = PermutationMatrix.getInstance(rows);
          int perms = pm.rows;
          for (int p=0;p<perms;p++)
          {
              double mul = 1;
              for (int i=0;i<rows;i++)
              {
                  mul *= get(i, pm.get(p, i));
              }
              sum += sign*mul;
              sign = -sign;
          }
          return sum;
      }