compute_total_tracer Function

   function compute_total_tracer(hTr, areaT, nghost) result(total)
      !! `Σ hTr(i,j,k)·areaT(i,j)` over PHYSICAL cells (ghosts excluded).
      !! Same explicit-reduction pattern as `compute_total_h`.
      real(wp), intent(in) :: hTr(:, :, :)
      real(wp), intent(in) :: areaT(:, :)
      integer, intent(in) :: nghost
      real(wp) :: total
      real(wp) :: acc
      integer :: i, j, k, nx, ny, nz, i_lo, i_hi, j_lo, j_hi
      nx = min(size(hTr, 1), size(areaT, 1))
      ny = min(size(hTr, 2), size(areaT, 2))
      nz = size(hTr, 3)
      i_lo = nghost + 1
      i_hi = nx - nghost
      j_lo = nghost + 1
      j_hi = ny - nghost
      acc = 0.0_wp
      !$acc parallel loop collapse(3) reduction(+:acc) present(hTr, areaT)
      do k = 1, nz
         do j = j_lo, j_hi
            do i = i_lo, i_hi
               acc = acc + hTr(i, j, k)*areaT(i, j)
            end do
         end do
      end do
      total = acc
   end function compute_total_tracer