code: def hessian(self, x, y, kwargs, k=None):
          
          return self.lens_model.hessian(x, y, kwargs, k=k)
docs: hessian matrix
  
          :param x: x-position (preferentially arcsec)
          :type x: numpy array
          :param y: y-position (preferentially arcsec)
          :type y: numpy array
          :param kwargs: list of keyword arguments of lens model parameters matching the lens model classes
          :param k: only evaluate the k-th lens model
          :return: f_xx, f_xy, f_yy components