[Developers] HydroBase infrastructure

[Erik Schnetter]

Dear GR Hydro Developers

Tanja Bode, Roland Haas, Frank Löffler, and I have taken up again the  
idea of a common HydroBase thorn.  This thorn would form a common  
basis for all or most GR hydro codes in much the same way that ADMBase  
is a common basis for most spacetime codes.  It would thus simplify  
writing initial data or analysis methods for GR hydro, and by  
explicitly providing standards defining e.g. what quantities initial  
data routines must provide would also prevent certain kinds of errors.

We have designed a prototype for a HydroBase thorn and are now looking  
for feedback.  You can find a snapshot of the prototype at <http://www.cct.lsu.edu/~knarf/HydroBase.tar.bz2 
 >.

Our current design has the following feature details:
- a common definition for the primitive variables
- the conserved (evolved) variables are still defined by the hydro  
evolution thorn
- common schedule groups for initial data, RHS calculation, boundary  
conditions, etc.
- common parameters to choose the number of time levels, hydro  
prolongation method, etc.
- HydroBase does not contain any source code
- initial data are supposed to be provided for the primitive variables  
only
- the pressure is considered a primitive variable

We plan to extend this thorn to:
- include variables for magnetic fields
- use TmunuBase as hydro interface (instead of CalcTmunu.inc)
- provide routines calculating Tmunu from the primitive variables

We hope that HydroBase can become a community standard.  Given the  
prevalence of Whisky, we kept things compatible with Whisky as much as  
possible, and we estimate that it should be very easy to modify Whisky  
to make use of HydroBase.  We're especially looking for feed from  
developers of other GR hydro codes.

Tanja, Roland, Frank, Erik

-- 
Erik Schnetter <schnetter at cct.lsu.edu>   http://www.cct.lsu.edu/~eschnett/

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