I have been trying to make some dark matter density movies using the "all_cic" field, and have discovered that using "all_cic" can reliably cause yt to seg fault on the supercomputer I'm using (x86_64 linux cluster with kernel 2.6.32-504.8.1.el6.x86_64) using the tip of yt-dev (changeset fa08e386d0da).  The script that causes the crash is here:

After I turned up the log level and started using pdb to debug, I discovered that the line in the script that causes the seg fault is line 88:

dm_dens_x = my_reg[("deposit", "all_cic")].value

where my_reg is defined as (on line 82):

my_reg = ds.arbitrary_grid(left, right, dims=[1,800, 800])

After stepping through with pdb, it seems that the code dies in this function:

/mnt/home/oshea/yt-3/lib/python2.7/site-packages/sympy/core/basic.py(83)__new__()

with the traceback shown here:

Based on this traceback, it seems that there are problems with the unit system. 

Interestingly enough, though, this does not happen on every dataset - it seems to happen occasionally, but predictably.  For example, I can generate two images using this script, but it will seg fault on the third.  On a different dataset in the time series, it will produce one image and then seg fault on the second.  If I run the script over and over, it will eventually produce quite a few images, until it runs into a situation where it seg faults on the first image I produce (at which point I went to the debugger).

I don't have enough experience with the guts of yt - and the units section of yt in particular - to have a sense of what might be happening here based on the traceback.  Does anybody have any suggestions?

Thank you!

--Brian