Hi,

I have not used Gadget, but ran into a similar problem recently and it was because of the PartType0 definition (basically).  Do you have a field "particle_type" or something like that?  I would print that as well and see if you are finding particles that are not "PartType0" within your sphere.  

Best,
Stephanie

--
Dr. Stephanie Tonnesen
Associate Research Scientist
CCA, Flatiron Institute
New York, NY

stonnes@gmail.com


On Tue, Mar 30, 2021 at 5:10 PM <h.fathie@gmail.com> wrote:
Dear all,

I have read a Gadget snapshot as follows:
ds = yt.load('../GadgetDiskGalaxy/snapshot_200.hdf5')
partID = ad[('PartType0', 'ParticleIDs')]

I then defined a sphere around a Type0 particle using the following lines of code:
j = 9000
sp = ds.sphere([px[j],py[j],pz[j]],(20.0,'kpc'))

When I issue the following command:
print(sp["particle_index"])
I get:

[ 841624.  890649.  841457.  890473.  865599.  865772. 6258099. 5752659.
 5752660. 5777940. 6229883. 5803543.] dimensionless

This shows that there are 12 particles inside the sphere.

I checked and found that the following IDs exist in the 'partID' array:
841624.  890649.  841457.  890473.  865599.  865772.

but these IDs (see below) do NOT exist in the 'partID' array:
6258099. 5752659. 5752660. 5777940. 6229883. 5803543
So the IDs of these 6 particles inside the sphere do not exist in the 'partID' array.

How is this possible since 'partID' (as defined above) must contain the IDs of all
Type0 particles ?

I would be grateful if someone could help me with this issue.
Best regards,
Hassan
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