[ET Trac] [Einstein Toolkit] #1238: implement buffer mask in CarpetEvolutionMask

[Einstein Toolkit]

#1238: implement buffer mask in CarpetEvolutionMask
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  Reporter:  rhaas        |       Owner:  eschnett           
      Type:  enhancement  |      Status:  review             
  Priority:  minor        |   Milestone:                     
 Component:  Carpet       |     Version:                     
Resolution:               |    Keywords:  CarpetEvolutionMask
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Comment (by eschnett):

 If you want to run in buffers or ghosts, then you can take the ibset
 corresponding to buffers and union it with the bboxes corresponding to
 ghosts. Ghosts are easy to identify; they are at the faces identified by
 cctk_bbox and have a width of cctk_nghostzones.

 On the other hand, if you need a weird combination of points which Carpet
 doesn't already identify, then you may as well use your own logic here.

 Note: The notion of "buffer points" is well defined in Carpet. The
 regridding algorithm (i.e. CarpetRegrid2) is supposed to specify a refined
 region that includes buffer points. Carpet will then take the outermost
 layer nbufferzones wide, and call these "buffer points". The remaining
 points are called "active".

 The exact rules are slightly more complex. For example, ghost points are
 added around the buffer points except at outer boundaries. Also, buffer
 points exist only near refinement boundaries, not near outer boundaries.
 Furthermore, there are "overlap points" between the active and the buffer
 points that I ignored in my description above. However, there is a well-
 defined algorithm determining which points are classified as what.

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Ticket URL: <https://trac.einsteintoolkit.org/ticket/1238#comment:8>
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