Add `fit_lines` method to spectrum

                                 for i in range(self.shape[0])])

        return res

    def fit_lines(self, redshift, **kwargs):

        """Use pyPLATEFIT to fit the spectrum lines.

        This method uses the `pyPLATEFIT.fit_mpdaf_spectrum` function to

        perform a line fitting. Refer to its documentation.

        Parameters

        ----------

        redshift : float

            Expected redshift of the spectrum.

        **kwargs : keyword arguments

            Additional arguments passed to the `fit_mpdaf_spectrum` function.

        Returns

        -------

        See pyPLATEFIT documentation.

        """

        try:

            from pyPLATEFIT import fit_mpdaf_spectrum

        except ImportError:

            raise ImportError("You need to install pyPLATEFIT.")

        return fit_mpdaf_spectrum(self, redshift=redshift, **kwargs)

    def plot(self, max=None, title=None, noise=False, snr=False,

             lmin=None, lmax=None, ax=None, stretch='linear', unit=u.angstrom,

             noise_kwargs=None, **kwargs):