void
cs_user_rad_transfer_absorption(const int         bc_type[],
    const cs_real_t   dt[],
    cs_real_t         ck[])
{
    /* Note: ck argument could be removed, access using field ids */
    {
        cs_real_t* cpro_cak0 = CS_FI_(rad_cak, 0)->val;
        assert(cpro_cak0 == ck);
    }

    /*< [abso_coeff] */
    /*
     * Absorption coefficient of the medium (m-1)
     *
     * In the case of specific physics (gas/coal/fuel combustion, elec),
     * Ck must not be defined here (it is determined automatically, possibly
     * from the parametric file)
     *
     * In other cases, Ck must be defined (it is zero by default)
     */

    if (cs_glob_physical_model_flag[CS_PHYSICAL_MODEL_FLAG] <= 1) {
        for (cs_lnum_t cell_id = 0; cell_id < cs_glob_mesh->n_cells; cell_id++)
            ck[cell_id] = 0.;
    }

    /*< [abso_coeff]*/

    /*< [abso_coeff_meteo] */

    {
        /* Read file the first time step */

        if (cs_glob_time_step->nt_cur <= cs_glob_time_step->nt_prev + 1) {

            /* Read from file */

            int n_v_segs = 77;
            cs_real_t zray2[78], k_up[78], k_down[78];

            FILE* f;
            float t;

            f = fopen("zray.dat", "r");
            for (int i = 0; i < n_v_segs + 1; i++) {
                fscanf(f, "%g", &t);
                zray2[i] = t;
            }
            fclose(f);
            f = fopen("kup.dat", "r");
            for (int i = 0; i < n_v_segs + 1; i++) {
                fscanf(f, "%g", &t);
                k_up[i] = t;
            }
            fclose(f);
            f = fopen("kdown.dat", "r");
            for (int i = 0; i < n_v_segs + 1; i++) {
                fscanf(f, "%g", &t);
                k_down[i] = t;
            }
            fclose(f);

            cs_field_t* f_ck_u = cs_field_by_name("rad_absorption_coeff_up");
            cs_field_t* f_ck_d = cs_field_by_name("rad_absorption_coeff_down");

            for (cs_lnum_t cell_id = 0; cell_id < cs_glob_mesh->n_cells; cell_id++) {

                cs_real_t z = cs_glob_mesh_quantities->cell_cen[cell_id * 3 + 2];

                /* Search for 1D cell */
                int iz = 0;

                cs_real_t tol = 1.0;
                /* Search loop */
                for (; iz < n_v_segs && z >(zray2[iz + 1] - tol); iz++);

                f_ck_u->val[cell_id] = fabs(k_up[iz + 1]);
                f_ck_d->val[cell_id] = fabs(k_down[iz + 1]);

            }
        }

    }
    /*< [abso_coeff_meteo] */
}