Hi Francia,

Looks to me like as it stands, you will have to calculate your center of mass manually.  (This is something we have addressed in the development branch, where it's a lot easier to do this kind of filtering, but it is not yet in the mainline branch.)  You can do it like this:

mx, my, mz = ((halo["particle_position_%" % ax][stars] * sm).sum()/sm.sum() for ax in 'xyz')

That should give you your center of mass in x, y, z for the stars.

-Matt


On Mon, Oct 21, 2013 at 12:07 PM, Francia Riesco <ff2214@columbia.edu> wrote:
Hello Everybody,
 I hope you are great!
 I have a question for you
I am analyzing an Enzo data trying to get the center of mass of the Stars Particles. I am suing FOF

linking_length = 0.017094633
haloes = FOFHaloFinder(pf, link=linking_length ,dm_only=False)
for halo in haloes:
    ct = halo["creation_time"]
    sm = halo["ParticleMassMsun"]
    metal = halo["metallicity_fraction"]
    stars = (ct > 0)
    ct = ct[stars]
    sm = sm[stars]



Is there a way to get sm.center_of_mass()  or something similar to get the Center of Mass of the Stars Particles??
Thank you in Advance !



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