[Users] GRHydro_c2p_failure_problem

[Roland Haas]

Hello Jimmy,

sorry for the late response. Unfortunately there is not usually a
simple fix to con2prim failures since it involves a non-linear root
finding with constraints. 

You may find that sometimes it helps to enable MHD simulation by
setting:

HydroBase::Bvec_evolution_method = "GRHdyro"

even though you are evolving a magnetic field of strength zero. Setting
this parameter selects a different con2prim routine that can be more
robust.

It can also help to increase resolution in particular since the gallery
example is quite poorly resolved.

Typically you would like to have a resolution of at least 0.1Msun (so
150m or so) for production simulations.

You can find some parameter files and discussion for production
simulations on the website of the University of Parma:

https://einstein.pr.infn.it/gravity/Research.html

Yours,
Roland

> Hi,
>   I've successfully run the gallery BNS simulation and as a second step, I try to replace the single polytropic EoS with the 7-segment SLyPP one mentioned in the 2021_ETK_Workshop. Mainly I made two substitutions in the original par file, I changed the Thorn EOS_Omni parameters into the hybrid form and I changed the type of the GRHydro_eos_table into "Hybrid". However, the simulation aborted due to the GRHydro_c2p_failure, as can be seen in the output .err file:
>  ----------------------------------------------------------------------
>   while executing schedule bin CCTK_POSTSTEP, routine GRHydro::check_GRHydro_C2P_failed
>   in thorn GRHydro, file GRHydro_Con2Prim.F90:1787:
>   ->                   xyz location:     14.06250       -5.625000        1.125000  
>  ----------------------------------------------------------------------
> I noticed that the failure point is near the outer layer of the neutron star. For clearance, I uploaded my par file and the err file. I wonder how to address this issue and I'm looking forward to your help.
> Yours,
> Jimmy

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