[ET Trac] [Einstein Toolkit] #181: AEILocalInterp should not off-centre the interpolation stencil by default

[Einstein Toolkit]

#181: AEILocalInterp should not off-centre the interpolation stencil by default
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  Reporter:  hinder  |       Owner:                
      Type:  defect  |      Status:  confirmed     
  Priority:  major   |   Milestone:                
 Component:  Cactus  |     Version:                
Resolution:          |    Keywords:  AEILocalInterp
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Comment (by eschnett):

 With periodic boundaries, which grid points are boundary points and which
 ones are evolved? Where are the grid points placed with respect to the
 boundary? There are basically three options: (1) an evolved grid point on
 the lower boundary, (2) an evolved grid point on the upper boundary, and
 (3) grid points staggered about the boundary. The two former go with
 vertex centred refinement, the latter with cell centred refinement.

 Where is the boundary located according to AEILocalInterp? If this thorn
 assumes that the boundary is directly at the outermost evolved grid point,
 then this notion clashes with what CoordBase chooses (see above), as
 boundary according to CoordBase will necessarily be located further
 outwards. Thus you might need to all off-centring the stencil, simply
 because AEILocalInterp's notion of what off-centring means is different
 from CoordBase's notion.

 Thorn CoordBase has some nice sketches explaining things that I tried to
 explain above.

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Ticket URL: <https://trac.einsteintoolkit.org/ticket/181#comment:6>
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