Inconsistent definition of B in evolution thorns
GRHydro and IllinoisGRMHD use different definitions for several quantities. This is mostly fine, as IllinoisGRMHD converts vel
to get its desired velocity variable. However, the magnetic variable B
also differs between these two thorns by a factor of sqrt(4pi)
. This means that GRHydro couldn't use, for example, initial data from the Seed_Magnetic_Fields thorns without rescaling them. Without an expectation for what B
is, diagnostic thorns that need this variable will produce incorrect results if used with anything except for the evolution thorn they were designed for. Presumably, all the WVUThorns are using IlliniosGRMHD’s B
, and GRHydro_InitData uses GRHydro’s B
. Anything that isn't explicitly tied to an evolution thorn would be ambiguous. Is there a consensus on what B
in HydroBase is expected to be?
Especially with the transition to CarpetX, having a single definition for B would likely help keep thorns mutually compatible.
Comments (2)
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I am surprised that there is no consensus about
HydroBase
; this should be documented in that thorn. Given historic precedence, I would go with the definition used inGRHydro
.HydroBaseX
should then use the same definition. - Log in to comment
Documented in:
https://bitbucket.org/einsteintoolkit/einsteinbase/src/db5777d1f921254d3e8d489c5b2e2b1c336113ef/HydroBase/interface.ccl#lines-15
and
https://bitbucket.org/einsteintoolkit/einsteinbase/src/master/HydroBase/doc/documentation.tex#lines-152
which hopefully is determining all factors for sqrt(4pi) uniquely. This has been a bit of a headache since the very beginning of GRHydro.