[Users] UIUC's GRMHD Primitives (Recovery) Solver

Christian D. Ott cott at tapir.caltech.edu
Tue Feb 19 17:27:02 CST 2013

Dear Zach,

sorry for the later reply -- we've all been very busy in the last few weeks.

Thank you for your email and sending us your con2prim code. We are very
happy to see you making code available as open source! Thank you very
much -- this is an important service to the broader community.

Making your code part of the Einstein Toolkit would be fantastic, but
would require a bit more help from your side -- just sending us code, is
unfortunately, not directly useful to the development of the toolkit.
Since our funding is very limited (our recent renewal ET grant was cut
by 50%; contributors in the EU and Canada don't have any funding for ET
at all), most of us spend our spare time to improve the toolkit by
actively maintaining it and integrating new code into the toolkit and
providing documentation for using the toolkit.

On http://einsteintoolkit.org/documentation/contribute/
we discuss how to contribute to the toolkit.

We would be very happy to have you and the rest of the UIUC group be
part of the ET development and maintenance team. If you are interested
in contributing to our ET work, please join our weekly telecons, which
take place on Monday (8am PST/11am EST). We would also be happy to
provide you with svn/git access to directly commit new code and carry
out maintenance tasks.

Best wishes,

  - Christian Ott

On 2/7/13 11:25 AM, Zach Etienne wrote:
> Dear ET folks,
> I had a recent discussion with Tanja Bode about the GRMHD primitives
> solver in Maya/ET. It seems both of our primitives (recovery) solvers
> (aka conservative-to-primitives routines) are based on the open-source
> HARM code, and there is a real push now to get GRMHD working in ET. The
> Illinois group would like to become more involved in contributing to the
> ET community, and as a show of our support, I am sending this email. I
> have discussed the situation with Stu Shapiro, who is happy to
> contribute and has permitted me to attach our HARM-based primitives
> solver to this email. This code is GPL version 2 or 3 (whichever you
> prefer to maximize compatibility with ET and the existing HARM license).
> As you are already familiar with HARM's solver, we include no
> documentation. The current solver can handle Gamma-law equations of
> state. It will require some work, but it should be straightforward to
> extend the solver to arbitrary equations of state.
> The solver contains a driver with some quality-control features, like
> taking a norm of how much the conservatives have changed before and
> after the solver. It also contains a standalone version, so that when
> the solver fails during a run, it can dump a file with all the
> information necessary to rerun the solver *independently of the
> evolution code* and debug the solver. It also outputs benchmarks (#
> primitives/second) by default each time it is called. Finally, it
> includes all of the fixes our group has developed over the years (see
> appendix in Etienne et al., Phys. Rev. D 85, 064029 (2012)) to assess
> and repair the physicality of conservatives *before* going through the
> Newton-Raphson routine, as well as fixing unphysical primitives when
> they appear. With these features, we have some confidence in the
> robustness of our solver.
> There are parts of the code where you'll find commented-out lines, as
> evidence that a lot of tweaking has gone into this. As with all of our
> codes, this solver is a work in progress. As we haven't used it, we
> haven't updated the standalone solver in a while, so you may need to
> port some of the features from primitives_generic.C if you would like to
> use the standalone version.
> -Zach, on behalf of the Illinois group
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