code: def _get_jacobian_hessian_strategy(self):
          
          if self.jacobian is not None and self.hessian is None:
              jacobian = None
              hessian = 'cs'
          elif self.jacobian is None and self.hessian is None:
              jacobian = 'cs'
              hessian = soBFGS(exception_strategy='damp_update')
          else:
              jacobian = None
              hessian = None
          return jacobian, hessian
docs: Figure out how to calculate the jacobian and hessian. Will return a
          tuple describing how best to calculate the jacobian and hessian,
          repectively. If None, it should be calculated using the available
          analytical method.
  
          :return: tuple of jacobian_method, hessian_method