// Set grid functions to nan
        auto mfitinfo = MFItInfo().SetDynamic(true).EnableTiling(
            {max_tile_size_x, max_tile_size_y, max_tile_size_z});
#pragma omp parallel
        for (MFIter mfi(*leveldata.mfab0, mfitinfo); mfi.isValid(); ++mfi) {
          GridPtrDesc grid(leveldata, mfi);
          const int tl = 0;
          const Array4<CCTK_REAL> &vars = groupdata.mfab.at(tl)->array(mfi);
          for (int vi = 0; vi < groupdata.numvars; ++vi) {
            CCTK_REAL *restrict const ptr = grid.ptr(vars, vi);
            grid.loop_all(groupdata.indextype, [&](const Loop::PointDesc &p) {
              ptr[p.idx] = 0.0 / 0.0;
            });
          }
        }