[Yt-dev] RMS mass overdensity method

[Matthew Turk]

> I've been working on trying to narrow down the focus, and it seems that cutting a sphere out many times causes problems. Below, between lines 67 and 73 you can see that I've de-randomized the center, so the sphere is the same every time. This eliminates potential problems of reading data outside each sub-box. I am also not retrieving ParticleMassMsun at all. It still crashes at variable points, one time similar to a standard run, one time a bit further.

Okay, so if it's a problem with cutting out a sphere too many times,
we should be able to replicate it with something like:

for i in xrange(1000):
    print i
    sp = pf.h.sphere([0.5, 0.5, 0.5], 1.0)

and that should kill it, right?

I think it would really help if we could eliminate all of the comments
and unused code and just strip this down into absolutely the smallest
thing that crashes.  I am now getting increasingly concerned this is a
bug in the broader YT codebase that you are the first person to run
into, but we need to be able to verify this.

> Do you have ideas of what I should try next? Is there anywhere I can put some prints that would help us debug this? Should I switch tatics and instead extract the particle data out and use a KDTree?

Don't use the KDTree, it will be slower and will require more
long-term persistent loading of data.  :)  For now, let's strip this
down to the 100% barest minimum.  I have RD0035 of the L7 run, so if
we can get this as tiny as possible I can run it on our machines here.
 I think that is our tactic.  Remove all comments, just the smallest
thing you think should crash.

-Matt