def METHOD_NAME(self, fileName, **kwargs):
    """Load simple data matrix."""
    mat = np.loadtxt(fileName)
    if len(mat[0]) == 4:
        self.fop.setDataSpace(ab2=mat[:, 0], mn2=mat[:, 1])
        return mat.T
    if len(mat[0]) == 6:
        self.complex = True
        self.fop.setDataSpace(ab2=mat[:, 0], mn2=mat[:, 1])
        return (mat[:, 0], mat[:, 1],
                np.array(pg.cat(mat[:, 2], mat[:, 4])),
                np.array(pg.cat(mat[:, 3], mat[:, 5])))