def set_dtreat_indlamb(self, indlamb=None):
        """ Store the desired index array for the wavelength

        If None => all wavelengths
        Must be a 1d array

        """
        if not self._isSpectral():
            msg = "The wavelength can only be set with DataSpectral object !"
            raise Exception(msg)
        if indlamb is not None:
            indlamb = np.asarray(indlamb)
            assert indlamb.ndim==1
            indlamb = _format_ind(indlamb, n=self._ddataRef['nlamb'])
        self._dtreat['indlamb'] = indlamb
        self._ddata['uptodate'] = False
Store the desired index array for the wavelength

        If None => all wavelengths
        Must be a 1d array