[ET Trac] [Einstein Toolkit] #755: Provide better support for implementing boundary conditions

[Einstein Toolkit]

#755: Provide better support for implementing boundary conditions
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  Reporter:  hinder       |       Owner:     
      Type:  enhancement  |      Status:  new
  Priority:  major        |   Milestone:     
 Component:  Cactus       |     Version:     
Resolution:               |    Keywords:     
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Comment (by eschnett):

 This macro loops over all physical boundaries. The blo/bhi parameters are
 the 6 boundary widths. What is missing is code to determine the boundary
 widths, and to distinguish between physical/symmetry/inter-process
 boundaries. (This information should be provided by CoordBase.)

 We could augment this macro with flags specifying over which boundaries to
 loop. We could also augment the macro to loop in 26 steps instead of in 6
 steps, and to provide normal information.

 There are some ambiguities because a boundary can be an inter-process, a
 physical, and a symmetry boundary at the same time (if it is a corner). In
 this case the caller needs to specify what should happen, e.g. "loop over
 all outer boundaries but exclude all ghost zones"; this allows taking
 tangential derivatives. Or "... but include ghost zones"; this does not
 require synchronisation afterwards. Depending on whether symmetry points
 are skipped, one may have to schedule the boundary condition after the
 symmetry condition. And so on.

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Ticket URL: <https://trac.einsteintoolkit.org/ticket/755#comment:3>
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