SIP04 data import

        Parameters
        ----------
        filename: string
            Path to .mat or .csv file containing SIP-04 measurement results

        Examples
        --------

        ::

            import tempfile
            import reda
            with tempfile.TemporaryDirectory() as fid:
                reda.data.download_data('sip04_fs_01', fid)
                sip = reda.SIP()
                sip.import_sip04(fid + '/sip_dataA.mat')

def import_sip04(self, filename, timestep=None):
        """SIP04 data import

        Parameters
        ----------
        filename: string
            Path to .mat or .csv file containing SIP-04 measurement results

        Examples
        --------

        ::

            import tempfile
            import reda
            with tempfile.TemporaryDirectory() as fid:
                reda.data.download_data('sip04_fs_01', fid)
                sip = reda.SIP()
                sip.import_sip04(fid + '/sip_dataA.mat')

        """
        df = reda_sip04.import_sip04_data(filename)
        if timestep is not None:
            print('adding timestep')
            df['timestep'] = timestep

        self._add_to_container(df)
        print('Summary:')
        self._describe_data(df)