Hi Stephanie, Hmm, this is curious. My first inclination is to suggest comparing the particle_index or particle_ones fields rather than mass, to make sure we're looking at precisely the same information. If that's not the culprit, then we should investigate if the *grids* are being passed over by sphere selection or if the particles themselves are. On Thu, Feb 25, 2021 at 3:00 PM Stephanie Tonnesen <stonnes@gmail.com> wrote:
Hi yt-users,
I have a question about spheres, because I am having a problem that I don't really know how to solve. Basically, I have clusters of stars, and I want to know how many stars are within 6 pc of each star. So, what I have done is taken a sphere at each star position with a radius of 6 pc, and then performed
sp.quantities.total_quantity(["particle_mass"])
Now I wanted to double-check this number by brute-force, so I calculated the distance between all the particles and then summed the masses of all the particles that were less than 6 pc.
I am not getting the same values--they are close, but not the same (they seem to mostly scatter up or down by a factor of 2).
So...to the question!! Because I am measuring particles in a grid code (Enzo) is there any sort of shifting to the grid position instead of using the particle positions here? Because stars are pretty packed I could imagine that this could cause the differences I am seeing.
I am not sure that the problem is not something silly I am doing, but wanted to check this possibility as well.
Thanks! Stephanie
-- Dr. Stephanie Tonnesen Associate Research Scientist CCA, Flatiron Institute New York, NY
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