code: def get_jac(self):
          
          if self._jac is True:
              if self.band is None:
                  f = self.be.Matrix(self.nf, 1, self.exprs)
                  _x = self.be.Matrix(self.nx, 1, self.x)
                  return f.jacobian(_x)
              else:
                  # Banded
                  return self.be.Matrix(banded_jacobian(
                      self.exprs, self.x, *self.band))
          elif self._jac is False:
              return False
          else:
              return self._jac
docs: Return the jacobian of the expressions