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

* status: new => review

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

Comment (by anonymous):

There is a difference, for instance, for syncing. Previously, the AtmosphereReset routine was scheduled in CCTK_EVOL after MoL_Evolution which required an extra sync of the primitive and conserved outside MoL_Evolution.

Instead, if we do the AtmosphereReset in the last Post Step, we only need to sync the primitives once (in the last post step), and in total we save an additional sync of the conserved quantities (since they are synced after Con2Prim anyway).

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

Comment (by eschnett):

This implies that:

(1) Atmosphere resetting acts locally on grid points, i.e. does not need ghost zones (does not look at neighbouring points), since otherwise it would require synchronizing beforehand. (2) It does not act on all grid points, since it requires synchronizing afterwards.

This seems strange. Could one instead run atmosphere resetting on all grid points (similar to converting to ADMBase), so that one does not need to synchronize afterwards?

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

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.

#841: MoL flag for last MoL_PostStep -----------------------------------------+---------------------------------- Reporter: reisswig@… | Owner: Type: enhancement | Status: closed Priority: optional | Milestone: Component: Cactus | Version: Resolution: wontfix | Keywords: MoL last PostStep flag -----------------------------------------+---------------------------------- Changes (by eschnett):

* status: review => closed * resolution: => wontfix

Comment:

Since there was further discussion, I will close this ticket.