using namespace Loop;
using namespace std;

template <typename T>
T lap(const Loop::GF3D<const T, 1, 1, 1> &var, const Loop::PointDesc &p) {
  const auto DI = Loop::vect<int, Loop::dim>::unit(0);
  const auto DJ = Loop::vect<int, Loop::dim>::unit(1);
  const auto DK = Loop::vect<int, Loop::dim>::unit(2);
  return fabs(var(p.I - DI) - 2 * var(p.I) + var(p.I + DI)) +
         fabs(var(p.I - DJ) - 2 * var(p.I) + var(p.I + DJ)) +
         fabs(var(p.I - DK) - 2 * var(p.I) + var(p.I + DK));

template <typename T, int CI, int CJ, int CK>
T lap(const GF3D<const T, CI, CJ, CK> &var, const vect<int, dim> &I) {
  const auto DI = vect<int, dim>::unit(0);
  const auto DJ = vect<int, dim>::unit(1);
  const auto DK = vect<int, dim>::unit(2);
  return fabs(var(I - DI) - 2 * var(I) + var(I + DI)) +
         fabs(var(I - DJ) - 2 * var(I) + var(I + DJ)) +
         fabs(var(I - DK) - 2 * var(I) + var(I + DK));

  const Loop::GF3D<CCTK_REAL, 1, 1, 1> regrid_error_(cctkGH, regrid_error);

  const GF3D<CCTK_REAL, 1, 1, 1> regrid_error_(cctkGH, regrid_error);

  Loop::loop_int<1, 1, 1>(cctkGH, [&](const Loop::PointDesc &p) {

  loop_int<1, 1, 1>(cctkGH, [&](const PointDesc &p) {