def _get_max_sigma(self, R):
        """Calculate maximum sigma of scanner RAS coordinates

        Parameters
        ----------

        R : 2D array, with shape [n_voxel, n_dim]
            The coordinate matrix of fMRI data from one subject

        Returns
        -------

        max_sigma : float
            The maximum sigma of scanner coordinates.

        """

        max_sigma = 2.0 * math.pow(np.nanmax(np.std(R, axis=0)), 2)
        return max_sigma
Calculate maximum sigma of scanner RAS coordinates

        Parameters
        ----------

        R : 2D array, with shape [n_voxel, n_dim]
            The coordinate matrix of fMRI data from one subject

        Returns
        -------

        max_sigma : float
            The maximum sigma of scanner coordinates.