[Users] problem using McLachlan with a NS-BH system

[Erik Schnetter]

The issue with the time step size (see probably
<https://arxiv.org/abs/1003.0859>) occurs on the coarsest levels only.
If the error occurs near the puncture on the fine grid, then this is
not the problem.

Some of the gauge parameters have a dimension (e.g. 1/length). The
"standard" settings are optimized for M=1. If your black hole mass is
very different, then you might need to change them. If you have a
total mass of M=4, then the gauge might try to act four times faster
than usual, leading to an instability. The cure would then be
increased resolution, or changing the respective parameters.

-erik



On Wed, Nov 27, 2019 at 8:52 AM Wolfgang Kastaun <physik at fangwolg.de> wrote:
>
> Hi Bruno,
>
> Not sure if related, but I vaguely recall that the gamma-driver shift
> gauge condition can become unstable if the timestep exceeds a critical
> value related to the damping constant eta in the driver. This might
> happen with 9 levels if the timestep is also increasing by a factor 2
> with each level. The solution I remember was to use the same timestep
> for the few coarsest levels. Do you know if the first occurrence of NANs
> in the shift happens on the coarsest level?
>
> Cheers,
> Wolfgang.
>
> On 11/27/19 12:36 PM, Bruno Giacomazzo wrote:
> > Dear All,
> >   a student of mine (Giulia Crotti) is having issues running a NS-BH
> > simulation with GRHydro and McLachlan (parfile attached). The problem we
> > are having is with the metric evolution (see attached image for the
> > lapse produced just before the crash) and I don't think I ever saw such
> > a problem. Does any of you have any suggestio?
> >
> > Approximately around 2000 iterations the simulation crashes with the
> > following error:
> >
> > ERROR from host r168c12s01.marconi.cineca.it
> > <http://r168c12s01.marconi.cineca.it> process 0
> >
> >   while executing schedule bin CCTK_EVOL, routine
> > PunctureTracker::PunctureTracker_Track
> >
> >   in thorn PunctureTracker, file
> > /marconi/home/userexternal/gcrotti0/EinsteinToolkit/ET_2018_09/Cactus/arrangements/EinsteinAnalysis/PunctureTracker/src/puncture_tracker.cc:204:
> >
> >   -> Shift at puncture #0 is (-nan,-nan,-nan).  This likely indicates an
> > error in the simulation.
> >
> >
> > Something is wrong with the metric; indeed the lapse function gets
> > larger than 1. We have 9 refinement levels on the black hole, with a
> > resolution of 0.045 on the finest grid. The initial data have been
> > computed as to get a mass ratio = 3; so the black hole mass is ~4 solar
> > masses. The black hole is non-spinning.
> >
> >
> > Thanks,
> >
> > Bruno
> >
> >
> > --
> >
> > Prof. Bruno Giacomazzo
> > Department of Physics
> > University of Milano-Bicocca
> > Piazza della Scienza 3
> > 20126 Milano
> > Italy
> >
> > email: bruno.giacomazzo at unimib.it <mailto:bruno.giacomazzo at unimib.it>
> > phone: (+39) 02 6448 2321
> > web: http://www.brunogiacomazzo.org <http://www.brunogiacomazzo.org/>
> >
> > ----------------------------------------------------------------------
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> > Those who understand binary, and those who don't
> > ----------------------------------------------------------------------
> >
> >
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-- 
Erik Schnetter <schnetter at cct.lsu.edu>
http://www.perimeterinstitute.ca/personal/eschnetter/