[yt-users] Halo positions in merger trees

Jean-Claude Waizmann waizmann at ita.uni-heidelberg.de
Thu Aug 6 02:24:53 PDT 2009


Hi all,

I have the following problem, when I compare the results of a merger
tree created using fastBuildMerge.py for the most massive halo at z=0,
with the output of running hop manually, I get the following
discrepancy:

			#part	x	y	z	 
fastBuildMerge		33809	0.492	0.495	0.485
Hop(yt)manually		50931	0.5019	0.4981	0.4902
old enzohop		43815	0.5019	0.4981	0.4902

Visual inspection of slices show, that the last two positions are
correct. So I wonder why the merger_tree gives wrong values even though
it is calling the same Hop routine. I need the positions of the parent
halos for profiling, and a difference of 0.01 in position corresponds to
1.28 Mpc which is a lot for a galaxy cluster, and would spoil the
analysis.

The difference in mass between the first two is strange as well. Did
anybody encounter the same problem and/or knows where it is coming from?

Thanks!

Jean-Claude

 




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