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

        Inputs:

            * fluxDownTop: flux down at top
            * emission: emission from atmospheric levels (N)
              defaults to zero if not given

        Returns:

            * vector of downwelling radiative flux between levels (N+1)
              element 0 is the flux down to the surface.