Using Bridges with RAMSES data

[Eliza Diggins]

Hey all,

I'm wondering if I can get some assistance utilizing bridges between RAMSES snapshots. At current, I encounter errors when I run anything like the following:

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import pynbody as pyn

import numpy as np

# Loading the snapshots

o1,o2= pyn.load('output_00001'),pyn.load("output_00200")

# creating the bridge #

bridge = pyn.bridge.Bridge(o1.dm,o2.dm)

# filtering first ouput #

s = pyn.filt.Sphere(radius, center)

o2_filt = bridge(o1.dm[s])

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This returns the following odd error: 

RuntimeError: Stale reference to start or endpoint

The RAMSES outputs do include AMR gas particles, but I'm restricting the bridge to the DM particles, so I don't think that should be the issue!

Hopefully this is a relatively simple fix. Additionally, this might be an example worth adding to documentation as its likely one of the more useful cases that users might encounter!

Thanks for any insight you can lend!

Best,

Eliza Diggins

[Pontzen, Andrew]

Yes this is a strange case. The rather hidden problem is that o1.dm is a transitory object that has been deleted by the time it’s actually needed by the bridge.

To fix this, you must store and use it consistently, something like this:

o1_dm = o1.dm
o2_dm = o2.dm

bridge = pyn.bridge.Bridge(o1_dm, o2_dm)

s = pyn.filt.Sphere(radius, center)

o2_filt = bridge(o1_dm[s])

I agree it would be good to explain somewhere in the documentation, or at least make the error message a bit more explanatory, if anyone has time to do so

All the best

Andrew

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