[ET Trac] #2952: GRHayLET/IllinoisGRMHD convert_*_to_*.c magnetic sector subleties

[Maxwell Rizzo]

#2952: GRHayLET/IllinoisGRMHD convert_*_to_*.c magnetic sector subleties

 Reporter: Maxwell Rizzo
   Status: new
Milestone: 
  Version: 
     Type: bug
 Priority: minor
Component: EinsteinToolkit thorn

convert_HydroBase_to_IllinoisGRMHD.c

1. HydroBase Aphi is directly copied into IllinoisGRMHD phitilde on line [29](https://github.com/GRHayL/GRHayLET/blob/9b01f8839d44db2ba928d2af7d1bc6b5178d54eb/IllinoisGRMHD/src/convert_HydroBase_to_IllinoisGRMHD.c#L29). A comment in the interface says "# phitilde (=Phi*psi^6)", and another "sqrt{gamma} Phi", so I believe the direct copy is missing a factor of Psi^6 or sqrt(det gamma). It is also missing a `mag_factor` scaling of 1/4pi when compared to the Avec copying, I am not sure if it is correct without it or it should have it given `mag_factor`/`rescale_magnetics` is on by default.

2. IllinoisGRMHD Ax/Ay/Az are face centered staggered, Aphi is vertex centered. They are populated directly from HydroBase cell centered quantities. This is a bit subtle for Initial Data thorns to interface with properly, it is somewhat documented but could be a bit clearer.

convert_IllinoisGRMHD_to_HydroBase.c

1. Only HydroBase Bvec is repopulated. HydroBase Avec and Aphi are not refilled (probably due to centering mismatch). This is probably fine as the magnetic field is the more interesting quantity for diagnostics, but it could be useful for debugging or consistency.

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Ticket URL: https://bitbucket.org/einsteintoolkit/tickets/issues/2952/grhaylet-illinoisgrmhd-convert_-_to_-c
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