[Yt-dev] more non-unique particles in enzo and how to deal with them

[Stephen Skory]

Britton,

>Stephen's latest update of his new parallel hop to check for unique-ness of particle indices has shed light on another problem.  In a recent simulation run with the devel/trunk version of enzo, I have found the particle numbers are no longer unique when star particles are generated.  Originally, the star particle indices by adding to the number of dark matter particles, such that if you had N dm particles and M star particles, the dm particle indices when from 0 to N-1 and the star particle indices went from N to N+M-1.

Unfortunately, Ji-hoon Kim addressed this issue last month <http://hg.spacepope.org/week-of-code/rev/bc61ccd0f247>, which you may not be aware of. Obviously it's too late for this dataset!

>However, now it seems that the star particles simply go from 0 to M.  Before I go any further, I will mention that the star particles can be differentiated from the dark matter particles by the particle_type data, so we're not totally screwed.  The point is that for the time being, hop no longer works.  The question is this: what is the best solution for dealing with this?  I am more than willing to write something to remap the particle indices, but that doesn't fix the underlying problem.  I have already done something similar to this for a different application, so I can do it quickly.  OR, something can be done to hop to read in particle type.  Clearly, this question is mainly for Stephen, but anyone should feel free to weigh in.  What is the best solution?

I see several options. You could filter out all the stars like this:

notstars = (self._data_source["particle_type"] != star)

and then in HaloFinding.py add a '[notstars]' to all the arrays where the particle data is handled and handed off to Parallel HOP. If you have 'creation_time' you could just try setting 'dm_only=True' in the HaloFinder call.

I think you could easily write a script to fix the dataset itself (on a copy, not the original, of course). Use h5py to open the files, and read in the particle_index and particle_type fields. SO something like this:

pi = file["Grid00000234"]["particle_index"]
ct = file["Grid00000234"]["particle_type"]
tochange = (ct == star)
tochange *= (number of dark matter particles)
pi += tochange

and then delete the old particle_index field from the file, and replace it with this new pi array.

I'll let you know what else I come up with.

Good luck!

 _______________________________________________________
sskory at physics.ucsd.edu           o__  Stephen Skory
http://physics.ucsd.edu/~sskory/ _.>/ _Graduate Student
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