code: def _get_grad_method(self, data):
          r
  
          self.grad = self.trans_op(self.op(data) - self.obs_data)
docs: r"""Get the gradient
  
          This method calculates the gradient step from the input data
  
          Parameters
          ----------
          data : np.ndarray
              Input data array
  
          Notes
          -----
          Implements the following equation:
  
          .. math::
              \nabla F(x) = \mathbf{H}^T(\mathbf{H}\mathbf{x} - \mathbf{y})