def flux_down(self, fluxDownTop, emission=None):
if emission is None:<EOL><INDENT>emission = np.zeros_like(self.absorptivity)<EOL><DEDENT>E = np.concatenate((np.atleast_1d(fluxDownTop),emission), axis=-<NUM_LIT:1>)<EOL>return np.squeeze(matrix_multiply(self.Tdown, E[..., np.newaxis]))<EOL>
Compute upwelling radiative flux at interfaces between layers.

        Inputs:

            * fluxUpBottom: flux up from bottom
            * emission: emission from atmospheric levels (N)
              defaults to zero if not given

        Returns:
            * vector of upwelling radiative flux between levels (N+1)
              element N is the flux up to space.