CCTK_INT IN gi_res)

  CCTK_INT IN gi_res,
  CCTK_REAL IN reltol,
  CCTK_REAL IN abstol,
  CCTK_REAL OUT res_initial,
  CCTK_REAL OUT res_final)

# run.me:
# run.cores: 4
# run.memory: 1.0e9
# run.time: 60.0

CarpetX::out_tsv = no

  SolvePoisson(gi_sol, gi_rhs, gi_res);

  const CCTK_REAL reltol = 0.0;
  const CCTK_REAL abstol = 1.0e-12;
  CCTK_REAL res_initial, res_final;
  SolvePoisson(gi_sol, gi_rhs, gi_res, reltol, abstol, &res_initial,
               &res_final);
  CCTK_VINFO("Residual before solve: %g", double(res_initial));
  CCTK_VINFO("Residual after solve:  %g", double(res_final));