Import a .mat file with single potentials (A B M) into a pandas
    DataFrame

    Also export some variables of the md struct into a separate structure

def _read_mat_mnu0(filename):
    """Import a .mat file with single potentials (A B M) into a pandas
    DataFrame

    Also export some variables of the md struct into a separate structure
    """
    print('read_mag_single_file')

    mat = sio.loadmat(filename)

    df_emd = _extract_emd(mat)

    return df_emd