<div>Hi Prachi,</div><div><br></div><div>Unfortunately you've come across a fundamental limitation to the way we currently treat SPH data: we don't have a good way of calculating fields that need spatial derivatives on octree meshes at the moment.</div><div><br></div><div>I'm currently actively working on this (this week actually) as part of a larger refactoring and redesign of how we treat SPH data to eliminate the global octree mesh. This is a longish term project and probably won't be ready for a few months, so unfortunately I can't help you right now.</div><div><br></div><div>Sorry to not have more concrete advice...</div><div><br></div><div>Nathan</div><div><br><div class="gmail_quote"><div>On Wed, Dec 7, 2016 at 5:52 PM Prachi Parihar <<a href="mailto:pparihar@astro.caltech.edu">pparihar@astro.caltech.edu</a>> wrote:<br></div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div class="gmail_msg">Hi all, <div class="gmail_msg"><br class="gmail_msg"></div><div class="gmail_msg">I am trying to compute vorticity for a fire snapshot. I've put down a sphere (sp), and can access some other derived fields, but for some reason things like vorticity give me the following error. Does anyone have suggestions as to what I'm doing wrong? </div><div class="gmail_msg"><br class="gmail_msg"></div><div class="gmail_msg"><div style="font-size:12.8px" class="gmail_msg">>>> sp['gas','velocity_magnitude']</div><div style="font-size:12.8px" class="gmail_msg">YTArray([ 53724618.56288539,  48756921.3449135 ,  46197475.78549621, ...,</div><div style="font-size:12.8px" class="gmail_msg">        53664392.60568497,  46881343.68564206,  50050673.058614  ]) cm/s</div><div style="font-size:12.8px" class="gmail_msg">>>> sp['gas','vorticity_x']</div><div style="font-size:12.8px" class="gmail_msg">Traceback (most recent call last):</div><div style="font-size:12.8px" class="gmail_msg">  File "<stdin>", line 1, in <module></div><div style="font-size:12.8px" class="gmail_msg">  File "/home/prachi/anaconda2/lib/python2.7/site-packages/yt/data_objects/data_containers.py", line 281, in __getitem__</div><div style="font-size:12.8px" class="gmail_msg">    self.get_data(f)</div><div style="font-size:12.8px" class="gmail_msg">  File "/home/prachi/anaconda2/lib/python2.7/site-packages/yt/data_objects/data_containers.py", line 1295, in get_data</div><div style="font-size:12.8px" class="gmail_msg">    self._generate_fields(fields_to_generate)</div><div style="font-size:12.8px" class="gmail_msg">  File "/home/prachi/anaconda2/lib/python2.7/site-packages/yt/data_objects/data_containers.py", line 1315, in _generate_fields</div><div style="font-size:12.8px" class="gmail_msg">    fd = self._generate_field(field)</div><div style="font-size:12.8px" class="gmail_msg">  File "/home/prachi/anaconda2/lib/python2.7/site-packages/yt/data_objects/data_containers.py", line 318, in _generate_field</div><div style="font-size:12.8px" class="gmail_msg">    tr = self._generate_fluid_field(field)</div><div style="font-size:12.8px" class="gmail_msg">  File "/home/prachi/anaconda2/lib/python2.7/site-packages/yt/data_objects/data_containers.py", line 336, in _generate_fluid_field</div><div style="font-size:12.8px" class="gmail_msg">    rv = self._generate_spatial_fluid(field, ngt_exception.ghost_zones)</div><div style="font-size:12.8px" class="gmail_msg">  File "/home/prachi/anaconda2/lib/python2.7/site-packages/yt/data_objects/data_containers.py", line 359, in _generate_spatial_fluid</div><div style="font-size:12.8px" class="gmail_msg">    for i, chunk in enumerate(chunks):</div><div style="font-size:12.8px" class="gmail_msg">  File "/home/prachi/anaconda2/lib/python2.7/site-packages/yt/geometry/particle_geometry_handler.py", line 179, in _chunk_spatial</div><div style="font-size:12.8px" class="gmail_msg">    g = og.retrieve_ghost_zones(ngz, [], smoothed=True)</div><div style="font-size:12.8px" class="gmail_msg">AttributeError: 'ParticleOctreeSubset' object has no attribute 'retrieve_ghost_zones'</div></div></div><br><br>_______________________________________________<br class="gmail_msg"><br>yt-users mailing list<br class="gmail_msg"><br><a href="mailto:yt-users@lists.spacepope.org" class="gmail_msg" target="_blank">yt-users@lists.spacepope.org</a><br class="gmail_msg"><br><a href="http://lists.spacepope.org/listinfo.cgi/yt-users-spacepope.org" rel="noreferrer" class="gmail_msg" target="_blank">http://lists.spacepope.org/listinfo.cgi/yt-users-spacepope.org</a><br class="gmail_msg"><br></blockquote></div></div>