anchor.diff:      double precision :: loc(3), r, r_P, r_S
   
       logical          :: outer_boundary_test(3)
  +    integer          :: boundary_buf(3), idx(3)
   
       do k = lo(3), hi(3)
          loc(3) = problo(3) + (dble(k) + HALF) * dx(3)
  
positive.code: 
      use bl_constants_module, only: ZERO, HALF, TWO
      use meth_params_module, only: NVAR, URHO, UTEMP
      use prob_params_module, only: center, probhi, dim, Symmetry, physbc_lo, physbc_hi
      use probdata_module, only: max_tagging_radius, &
                                 max_stellar_tagging_level, &
                                 max_temperature_tagging_level, &
  
negative.code: 
               ! We must ensure that the outermost zones are untagged
               ! due to the Poisson equation boundary conditions.
               ! We currently do not know how to fill the boundary conditions
               ! for fine levels that touch the physical boundary.
               ! (Note that this does not apply for interior/symmetry boundaries.)
               ! To do this properly we need to be aware of BoxLib's strategy
               ! for tagging, which is not cell-based, but rather chunk-based.
               ! The size of the chunk on the coarse grid is given by
               ! blocking_factor / ref_ratio -- the idea here being that
               ! blocking_factor is the smallest possible group of cells on a
               ! given level, so the smallest chunk of cells possible on the
               ! coarse grid is given by that number divided by the refinement ratio.
               ! So we cannot tag anything within that distance from the boundary.
               ! Additionally we need to stay a further amount n_error_buf away,
               ! since n_error_buf zones are always added as padding around
               ! tagged zones.
  
               outer_boundary_test = .false.
               boundary_buf = n_error_buf(level) + blocking_factor(level+1) / ref_ratio(:, level)
               idx = [i, j, k]
  
               do n = 1, dim
  
                  if ((physbc_lo(n) .ne. Symmetry) .and. (idx(n) .le. domlo_level(n, level) + boundary_buf(n))) then
                     outer_boundary_test(n) = .true.
                  endif
  
                  if ((physbc_hi(n) .ne. Symmetry) .and. (idx(n) .ge. domhi_level(n, level) - boundary_buf(n))) then
                     outer_boundary_test(n) = .true.
                  endif
  
  