pro zero_solution_under_subgrid, u_g, all, ZERO=zero, all_grid_info = a_g
  if N_elements(a_g) eq 0 then a_g = u_g
  zero = (N_ELEMENTS(zero) gt 0) ? zero :  0. ; 0. is the default value
  N_grids = N_elements(u_g)
  ri = INTARR(3)
  FOR i=0L,N_grids-1 DO BEGIN
      ci = where(a_g.parent EQ u_g[i].num, count) ; list of indeces of grids that have me as parent
      IF (count GT 0) THEN BEGIN
          FOR jj=0L,N_ELEMENTS(ci)-1 DO BEGIN
; zeroing all data values where childs are:
              cc = ci[jj]
              li = (((a_g[cc].parent_s_index[*]) - all[i].li[*]) > 0 ) < (all[i].dims -1)
              for j=0L,N_elements(li)-1 do  $
                ri[j] = ((min([a_g[cc].parent_e_index[j], all[i].ri[j]])-all[i].li[j]) $
                         < (all[i].dims[j]-1)) > li[j]
;              print, 'zsus:', ri-li+1
              for j=0,all[i].N_Dfields-1 do begin
                 if all[i].np_total gt 0 then begin
                    ds = size(*all[i].data[j])
                    if ds[0] lt 1 then break
                    if N_elements(*all[i].data[j]) eq product(all[i].dims > 1) then begin
                       (*all[i].data[j])[li[0]:ri[0], li[1]:ri[1], li[2]:ri[2]] = zero 
;                       print, li, ri
                    endif else begin
                       print, 'zero_solution_under_subgrid: somethings wrong', a_g[cc].num, i, jj, j, $
                              all[i].data_fields[j], 'Ne:', N_elements(all[i].data[j]), product(all[i].dims),(all[i].dims)
;                       breaki
                    endelse
                 endif
              ENDFOR
          ENDFOR
      END 
  ENDFOR  
  RETURN
END