bc_ss_flux(AC_TOP_BOT topbot,bool lone_sided)
{
  real tmp_xy
  real cs2_xy
  real rho_xy
  int i
  bool loptest_return_value_1
  bool loptest_return_value_4
  if(topbot == AC_bot) {
    if (AC_pretend_lntt) {
      tmp_xy=-AC_fbotkbot/exp(SS[vertexIdx.x][vertexIdx.y][AC_n1-1])
      for i in 1:AC_NGHOST+1 {
        SS[vertexIdx.x][vertexIdx.y][AC_n1-i-1]=SS[vertexIdx.x][vertexIdx.y][AC_n1+i-1]-AC_dz2_bound[-i+AC_NGHOST+1-1]*tmp_xy
      }
    }
    else {
      if (AC_ldensity_nolog) {
        if (AC_lreference_state) {
          rho_xy= LNRHO[vertexIdx.x][vertexIdx.y][AC_n1-1]  +AC_reference_state_padded[vertexIdx.x][AC_iref_rho-1]
        }
        else {
          rho_xy=LNRHO[vertexIdx.x][vertexIdx.y][AC_n1-1]
        }
      }
      else {
        rho_xy=exp(LNRHO[vertexIdx.x][vertexIdx.y][AC_n1-1])
      }
      cs2_xy = SS[vertexIdx.x][vertexIdx.y][AC_n1-1]
      if (AC_lreference_state) {
        cs2_xy = cs2_xy + AC_reference_state_padded[vertexIdx.x][AC_iref_s-1]
      }
      if (AC_ldensity_nolog) {
        cs2_xy=AC_cs20*exp(AC_gamma_m1*(log(rho_xy)-AC_lnrho0)+AC_cv1*cs2_xy)
      }
      else {
        cs2_xy=AC_cs20*exp(AC_gamma_m1*(LNRHO[vertexIdx.x][vertexIdx.y][AC_n1-1]-AC_lnrho0)+AC_cv1*cs2_xy)
      }
      if (AC_lheatc_chiconst) {
        tmp_xy=AC_fbot/(rho_xy*AC_chi*cs2_xy)
      }
      else if (AC_lheatc_kramers) {
        tmp_xy=AC_fbot*pow(rho_xy,(2*AC_nkramers))*pow((AC_cp*AC_gamma_m1),(6.5*AC_nkramers))  /(AC_hcond0_kramers*pow(cs2_xy,(6.5*AC_nkramers+1.)))
      }
      else {
        tmp_xy=AC_cp*AC_fbotkbot/cs2_xy
      }
      if (present(lone_sided)) {
        loptest_return_value_1=lone_sided
      }
      else if (false) {
      }
      else {
        loptest_return_value_1=false
      }
      if (loptest_return_value_1) {
        print("not implemented getderlnrho_z")
        print("not implemented bval_from_arr")
        print("not implemented set_ghosts_for_onesided_ders")
      }
      else {
        for i in 1:AC_NGHOST+1 {
          rho_xy = LNRHO[vertexIdx.x][vertexIdx.y][AC_n1+i-1]-LNRHO[vertexIdx.x][vertexIdx.y][AC_n1-i-1]
          if (AC_ldensity_nolog) {
            if (AC_lreference_state) {
              rho_xy = rho_xy/(LNRHO[vertexIdx.x][vertexIdx.y][AC_n1-1]  +AC_reference_state_padded[vertexIdx.x][AC_iref_rho-1])
            }
            else {
              rho_xy = rho_xy/LNRHO[vertexIdx.x][vertexIdx.y][AC_n1-1]
            }
          }
          SS[vertexIdx.x][vertexIdx.y][AC_n1-i-1]=SS[vertexIdx.x][vertexIdx.y][AC_n1+i-1]+(AC_cp-AC_cv)*(rho_xy+AC_dz2_bound[-i+AC_NGHOST+1-1]*tmp_xy)
        }
      }
    }
  }
  else if(topbot == AC_top) {
    if (AC_pretend_lntt) {
      tmp_xy=-AC_ftopktop/exp(SS[vertexIdx.x][vertexIdx.y][AC_n2-1])
      for i in 1:AC_NGHOST+1 {
        SS[vertexIdx.x][vertexIdx.y][AC_n2-i-1]=SS[vertexIdx.x][vertexIdx.y][AC_n2+i-1]-AC_dz2_bound[i+1+AC_NGHOST-1]*tmp_xy
      }
    }
    else {
      if (AC_ldensity_nolog) {
        if (AC_lreference_state) {
          rho_xy= LNRHO[vertexIdx.x][vertexIdx.y][AC_n2-1]  +AC_reference_state_padded[vertexIdx.x][AC_iref_rho-1]
        }
        else {
          rho_xy=LNRHO[vertexIdx.x][vertexIdx.y][AC_n2-1]
        }
      }
      else {
        rho_xy=exp(LNRHO[vertexIdx.x][vertexIdx.y][AC_n2-1])
      }
      cs2_xy = SS[vertexIdx.x][vertexIdx.y][AC_n2-1]
      if (AC_lreference_state) {
        cs2_xy = cs2_xy + AC_reference_state_padded[vertexIdx.x][AC_iref_s-1]
      }
      if (AC_ldensity_nolog) {
        cs2_xy=AC_cs20*exp(AC_gamma_m1*(log(rho_xy)-AC_lnrho0)+AC_cv1*cs2_xy)
      }
      else {
        cs2_xy=AC_cs20*exp(AC_gamma_m1*(LNRHO[vertexIdx.x][vertexIdx.y][AC_n2-1]-AC_lnrho0)+AC_cv1*cs2_xy)
      }
      if (AC_lheatc_chiconst) {
        tmp_xy=AC_ftop/(rho_xy*AC_chi*cs2_xy)
      }
      else if (AC_lheatc_kramers) {
        tmp_xy=AC_ftop*pow(rho_xy,(2*AC_nkramers))*pow((AC_cp*AC_gamma_m1),(6.5*AC_nkramers))  /(AC_hcond0_kramers*pow(cs2_xy,(6.5*AC_nkramers+1.)))
      }
      else {
        tmp_xy=AC_cp*AC_ftopktop/cs2_xy
      }
      if (present(lone_sided)) {
        loptest_return_value_4=lone_sided
      }
      else if (false) {
      }
      else {
        loptest_return_value_4=false
      }
      if (loptest_return_value_4) {
        print("not implemented getderlnrho_z")
        print("not implemented bval_from_arr")
        print("not implemented set_ghosts_for_onesided_ders")
      }
      else {
        for i in 1:AC_NGHOST+1 {
          rho_xy = LNRHO[vertexIdx.x][vertexIdx.y][AC_n2+i-1]-LNRHO[vertexIdx.x][vertexIdx.y][AC_n2-i-1]
          if (AC_ldensity_nolog) {
            if (AC_lreference_state) {
              rho_xy = rho_xy/(LNRHO[vertexIdx.x][vertexIdx.y][AC_n2-1]  +AC_reference_state_padded[vertexIdx.x][AC_iref_rho-1])
            }
            else {
              rho_xy = rho_xy/LNRHO[vertexIdx.x][vertexIdx.y][AC_n2-1]
            }
          }
          SS[vertexIdx.x][vertexIdx.y][AC_n2+i-1]=SS[vertexIdx.x][vertexIdx.y][AC_n2-i-1]+(AC_cp-AC_cv)*(-rho_xy-AC_dz2_bound[i+1+AC_NGHOST-1]*tmp_xy)
        }
      }
    }
  }
  else {
  }
}