[Users] Einstein Toolkit 2012 Paper NS gravitational collapse example

[Roland Haas]

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Hello Vassilios,

> when i did the collapse (with less refinement levels and resolution
> due to RAM restrictions on my iMac) the code crashes as well after
> the Bh has been formed...when using AHfinderDirect, the simulation
> stops upon the following error:
> 
> [1mWARNING level 0 in thorn AHFinderDirect processor 0 host 
> permeability.daa.uv.es (line 78 of 
> /Users/vass/programs/Cactus/arrangements/EinsteinAnalysis/AHFinderDirect/src/jtutil/error_exit.cc):
>
> 
- -> [0m ***** row_sparse_Jacobian__UMFPACK::solve_linear_system():
> error return status=1 from umfpack_numeric() routine
> 
> and when running without the AHFinderdirect, the run produces
> meaningless results (the density maximum and minimum as well as the
> lapse min and max get set to 1.797693e+308 and -1.797693e+308)
> however, there are no NaNs caught by the NaNChecker...
The huge min/max of lapse would point to it picking up poison
somewhere. I would have expected NaNChecker (which checks only rho,
gxx and kxx) to trigger soon (it only checks every 64 iterations)
after. This actually sounds like a bug since there should never be
poison left one the grid. I'd have to re-run it again (did you use
current code or code from a previous release) to test what happens.
One can get the simulation to proceed after collapse but it takes a
bit of fine-tuning as far as I know.

> thanks for pointing out the trigger thorn, is it triggering more
> refinement levels once the density has reached a certain
> threshold?
Yes, that was the intention. Trigger allows general settings to be
made based on conditions. For each trigger there is a Trigger_Relation
parameter (which defaults to ">") that is used to evaluate the
condition. The ones I set up should increase the number of refined
levels to 6 and 7 when the density goes above 2.5e15 and 3.5e15
respectively.

> what about the general stability of simulations after a BH has been
> formed? is it yet possible to evolve the system for a long time
> after the formation of a BH, using the current tools available in
> the ET? i am asking this because we are interested in gravitational
> collapse of NS triggered by winds past the NS and it would be
> desirable to observe the long term evolution of the NS-wind and
> later BH-wind system...
One can get it to evolve afterwards as far as I know but it requires
some fine tuning and possibly use of more current code.

Yours,
Roland

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