[yt-users] Incorrect particle index for halo particles

Josh Moloney Joshua.Moloney at Colorado.EDU
Tue Mar 18 15:55:41 PDT 2014

Hi all,

I'm working on a script to calculate star formation rates for halos in
different mass bins from Enzo simulation ouput. As part of the script, I
need to access the dynamical_time values for all of the star particles
associated with a given halo. The halos have been previously stored to
disk, so I'm loading them with LoadHaloes and then for each halo
identifying the star particles with the typical

stars = halo["creation_time"] > 0

mask. When I try to get the associated dynamical times with


I get -99999. instead of the expected values. When I perform the same
operation on the entire dataset instead of an individual halo I get the
correct dynamical times, so the values I want do exist. I was testing out
different fields with


to see if I could find any patterns, and I noticed that for all the fields
that are actually saved to disk for the halos (creation_time,
ParticleMassMsun, particle_positions, etc.) I get values that match those
in the halo hdf5 files. However, this is not true for "particle_index",
where I get incorrect values. The values do correspond to particles in the
halo, but they aren't the indices of the star particles. I'm not sure, but
I assume this is why I'm getting incorrect values for dynamical_time which
isn't saved in the halo hdf5 files. I'm not familiar enough with the code
for the halo finder to know where to start looking for the source of this
problem. Does anyone with more experience have an idea? My version of yt is
a copy of 2.6.1 that I updated about 3 weeks ago. Thanks.
         - Josh
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