[ET Trac] [Einstein Toolkit] #1494: Allow skipping of MoL_PostStep and MoL_PseudoEvolutionBoundaries in POSTRESTRICT

[Einstein Toolkit]

#1494: Allow skipping of MoL_PostStep and MoL_PseudoEvolutionBoundaries in
POSTRESTRICT
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 Reporter:  hinder       |       Owner:                     
     Type:  enhancement  |      Status:  new                
 Priority:  minor        |   Milestone:                     
Component:  Cactus       |     Version:  development version
 Keywords:               |  
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 It is not always necessary to call MoL_PostStep and
 MoL_PseudoEvolutionBoundaries in POSTRESTRICT, and it can introduce a
 performance penalty.   The main reason for these calls is that restriction
 does not fill (outer or symmetry) boundary points, and this is usually
 done in MoL_PostStep.  MoL_PseudoEvolutionBoundaries also sets boundary
 conditions.  However, if restriction does not modify boundary points, for
 example in the case that boundary points are always far from refined
 regions, there is no reason to apply boundary conditions (e.g. by calling
 MoL_PostStep) after restriction.

 Eventually, Carpet and MoL should be modified to determine automatically
 whether the BCs need to be applied, but until that is implemented, the
 attached patch provides parameters for careful users to optimise their
 simulations in the case where this is safe to do.

 Additionally, recalculations performed in MoL_PostStep may replace more
 accurate restricted values computed on finer grids, leading to a loss of
 accuracy.

 OK to commit?

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Ticket URL: <https://trac.einsteintoolkit.org/ticket/1494>
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