[ET Trac] [Einstein Toolkit] #841: MoL flag for last MoL_PostStep

[Einstein Toolkit]

#841: MoL flag for last MoL_PostStep
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  Reporter:  reisswig@…                  |       Owner:                        
      Type:  enhancement                 |      Status:  review                
  Priority:  optional                    |   Milestone:                        
 Component:  Cactus                      |     Version:                        
Resolution:                              |    Keywords:  MoL last PostStep flag
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Comment (by reisswig):

 Yes, atmosphere resetting does not look at neighboring points and thus no
 need for ghostzones. And yes, it only acts on those grid points (nominal
 grid) which had a proper RHS update and were integrated by MoL.

 The trouble is that the atmosphere mask is updated during MoL evolution
 and can only be set on the nominal grid. We would need to synchronize the
 atmosphere mask. Then, we would be able to schedule atmosphere reset after
 all syncs and act on all grid points (and not just the nominal points).

 We could also put the flag to GRHydro (which does the atmo handling) and
 let GRHydro decide whether this is the last PostStep. However, there may
 also be other thorns like the neutrino leakage thorn which may require
 scheduling in the last post step.

 I principally agree that keeping the MoL thorn clean is a good idea. But I
 also see that the last MoL post step is a special case. For now, I guess
 we could introduce a flag to GRHydro checking the MoL step counter and let
 GRHydro decide whether it is time to execute the atmo resetting routine.

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Ticket URL: <https://trac.einsteintoolkit.org/ticket/841#comment:7>
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