def reddening(self,extval):
        """Compute the reddening for the given extinction.

        .. math::

            A(V) = R(V) \\; \\times \\; E(B-V)

            \\textnormal{THRU} = 10^{-0.4 \\; A(V)}

        .. note::

            ``self.litref`` is passed into ``ans.citation``.

        Parameters
        ----------
        extval : float
            Value of :math:`E(B-V)` in magnitudes.

        Returns
        -------
        ans : `~pysynphot.spectrum.ArraySpectralElement`
            Extinction curve to apply to a source spectrum.

        """
        T = 10.0**(-0.4*extval*self.obscuration)
        ans = ExtinctionSpectralElement(wave=self.wave,
                                        waveunits=self.waveunits,
                                        throughput=T,
                                        name='%s(EBV=%g)'%(self.name, extval))
        ans.citation = self.litref
        return ans
Compute the reddening for the given extinction.

        .. math::

            A(V) = R(V) \\; \\times \\; E(B-V)

            \\textnormal{THRU} = 10^{-0.4 \\; A(V)}

        .. note::

            ``self.litref`` is passed into ``ans.citation``.

        Parameters
        ----------
        extval : float
            Value of :math:`E(B-V)` in magnitudes.

        Returns
        -------
        ans : `~pysynphot.spectrum.ArraySpectralElement`
            Extinction curve to apply to a source spectrum.