Hi, I would like to compute some spacial derivatives for FLASH4 2D cylindrical uniform grid datafile with YT. For simplicity, I tried the example given in YT docs, although I know the derivative form is only valid for Cartesian, and this is just for code test purposes. My script are: @derived_field(name='DivV') # I do not use ValidateSpatial… ghost_zone… because the ghost cells are not stored in FLSAH check point file def DivV(field, data): sl_left = slice(None,-2) sl_right = slice(2,None) div_fac = 2.0 ds = div_fac * data['dx'].flat[0] f = data["velx"][sl_right,1:-1]/ds f -= data["vely"][sl_left ,1:-1]/ds ds = div_fac * data['dy'].flat[0] f += data["velx"][1:-1,sl_right]/ds f -= data["vely"][1:-1,sl_left]/ds new_field = na.zeros(data["velx"].shape, dtype='float64') new_field[1:-1,1:-1] = f return new_field Then, if I add: pf = load('relax_hdf5_chk_0001') pf.h.find_max('DivV') The script works, but if I use: dd = pf.h.all_data() print dd['DivV'].sum() and it will give error: yt : [INFO ] 2013-01-23 21:17:01,551 Getting field dx from 256 yt : [INFO ] 2013-01-23 21:17:01,625 Getting field velx from 256 Traceback (most recent call last): File "test.py", line 28, in <module> print dd['DivV'].sum() File "/usr/local/yt-i386/src/yt-hg/yt/data_objects/data_containers.py", line 330, in __getitem__ self.get_data(key) File "/usr/local/yt-i386/src/yt-hg/yt/data_objects/data_containers.py", line 2607, in get_data if self._generate_field(field): File "/usr/local/yt-i386/src/yt-hg/yt/data_objects/data_containers.py", line 360, in _generate_field self[field] = self.pf.field_info[field](self) File "/usr/local/yt-i386/src/yt-hg/yt/data_objects/field_info_container.py", line 378, in __call__ dd = self._function(self, data) File "test.py", line 11, in DivV f = data["velx"][sl_right,1:-1]/ds IndexError: too many indices Nor can I make slice plot for this field. I would appreciate your suggestions for this issue. Best wishes, Suoqing