def _op_method(self, data, extra_factor=1.0):
        """Operator

        This method returns the input data after the singular values have been
        thresholded

        Parameters
        ----------
        data : np.ndarray
            Input data array
        extra_factor : float
            Additional multiplication factor

        Returns
        -------
        np.ndarray SVD thresholded data

        """

        # Update threshold with extra factor.
        threshold = self.thresh * extra_factor

        if self.lowr_type == 'standard':
            data_matrix = svd_thresh(cube2matrix(data), threshold,
                                     thresh_type=self.thresh_type)

        elif self.lowr_type == 'ngole':
            data_matrix = svd_thresh_coef(cube2matrix(data), self.operator,
                                          threshold,
                                          thresh_type=self.thresh_type)

        new_data = matrix2cube(data_matrix, data.shape[1:])

        # Return updated data.
        return new_data
Operator

        This method returns the input data after the singular values have been
        thresholded

        Parameters
        ----------
        data : np.ndarray
            Input data array
        extra_factor : float
            Additional multiplication factor

        Returns
        -------
        np.ndarray SVD thresholded data