[Carpet] Changes to regridding

[Erik Schnetter]

On May 1, 2006, at 05:39:20, Bela Szilagyi wrote:

> Yet another related issue --
>
> I find it slightly inconvenient that Carpet schedules "PostRegrid"  
> at recovery
> the same way as when a true (during-evolution) regridding was done.
>
> Not mentioning that it is possible to get core dumps by trying to  
> change the
> grid-structure at recovery,

Hm.  You are not really supposed to do that.  Carpet has currently a  
missing feature, namely that it does not store the grid structure in  
the checkpoint file.  It is therefore necessary to specify the  
correct grid structure in the parameter file that you use to  
recover.  It is, within certain bounds, possible to change the grid  
structure (e.g. having fewer levels), but that was not originally  
intended and is not really supported.  It is also not strictly  
necessary, since there will be a regridding step after recovering and  
before the next time step.

> the major issue I have is:  could we call the
> recovery group some other name, say "PostRegridAtRecovery".  The  
> same would
> hold for "PreRegrid"...

I'm afraid that this is not feasible.  After recovering, Carpet jumps  
directly into the routine that performs the next time step.  The  
first thing happening in this routine is regridding.  There is  
nothing special about this regridding and the regridding that occurs  
before every time step.  We could make the first time step after  
recovering special, but this would introduce the possibility of  
strange errors that are difficult to find, where checkpointing and  
recovering would lead to different results.

At some time in the future, Carpet will store the grid structure in  
the checkpoint file, and will use this stored grid structure after  
recovering.  If you want to change the grid structure, you have to do  
that in an explicit manner after recovering.

-erik

-- 
Erik Schnetter <schnetter at cct.lsu.edu>

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