[Users] error when I trying to add atmosphere to BBH evolution

[Roland Haas]

Hello all,

> Could you give more details about the physics you are trying to add?
> "atmosphere" in this context usually means an artificial low density
> fluid in a matter simulation which helps with numerical problems that
> occur when the density drops to zero.  It doesn't make sense to add
> it to a BBH simulation, which is vacuum.
> 
> Do you mean that you want to add a low density fluid to a BBH
> simulation?
In case you are planning something similar to
https://arxiv.org/abs/1704.07383 then you may want to contact the first author (Joseph Fedrow) possibly through this list (he's subscribed). Typically you will get failures of con2prim near the punctures and have to take special measures to work around it. 

Usually this involves setting

* GRHydro::recon_method = ppm # since it is very robust
* GRHydro::reconstruct_Wv = yes # avoids some v^2>c^2 situations
* GRHydro::riemann_solver = "Marquina" # better than HLLE for this
* GRHydro::sqrtdet_thr = 10. # or so, these apply Joshua Faber's
  methods described in https://arxiv.org/abs/0708.2436
* GRhydro::c2p_resort_to_bisection = yes # try bisection if
  Newton-Raphson iteration fails

Note that my recollection of the paper by Fedrow (I am a co-author) was
that all of those were required but not quite enough and that Christian
Ott had to write a special con2prim routine that handled the BH interior
carefully.

There is a also code in TwoPunctures that can solve the constraints
(the TP code is in the ET but not the code that eg provides a density
profile). Again best would be to contact the authors (all reachable
through this list).

Yours,
Roland

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