Hi all,

I am trying to run Rockstar Halo Finding with the following code.

from yt.mods import *
from yt.analysis_modules.halo_finding.rockstar.api import RockstarHaloFinder

#find all of our simulation files
files = glob.glob("RD*/*hierarchy")

#hopefully the file name order is chronological
print files

ts = TimeSeriesData.from_filenames(files[:])
rh = RockstarHaloFinder(ts)

but I am getting the following error. 
 File "rockstar_halo_finding.py", line 14, in <module>
    rh = RockstarHaloFinder(ts)
  File "/home/john/yt_new/yt-x86_64/src/yt-hg/yt/analysis_modules/halo_finding/rockstar/rockstar.py", line 220, in __init__
    self.pool, self.workgroup = self.runner.setup_pool()
  File "/home/john/yt_new/yt-x86_64/src/yt-hg/yt/analysis_modules/halo_finding/rockstar/rockstar.py", line 102, in setup_pool
    (self.num_writers, "writers") ]
  File "/home/john/yt_new/yt-x86_64/src/yt-hg/yt/utilities/parallel_tools/parallel_analysis_interface.py", line 325, in from_sizes
    pool.add_workgroup(size, name = name)
  File "/home/john/yt_new/yt-x86_64/src/yt-hg/yt/utilities/parallel_tools/parallel_analysis_interface.py", line 293, in add_workgroup
    group = self.comm.comm.Get_group().Incl(ranks)
AttributeError: 'NoneType' object has no attribute 'Get_group'

could you please explain what is going wrong here ?

Thank you. 
Reju Sam John