[Carpet] checkpoint and regridding

[Erik Schnetter]

On Nov 26, 2007, at 03:58:50, Luca Baiotti wrote:

> Hi Erik,
>
> would you have any doubts that there may be a problem in carpet  
> when restarting a simulation from a checkpoint that was written on  
> the same iteration when a regridding took place? I was wondering  
> maybe about how and which past timelevels are stored. Actually, I  
> don't really know: after a regridding, what happens to the past  
> timelevels? They have a different grid structure, right?

Hi Luca,

yes, there could be problems with checkpointing... however, the only  
problems of which I know are those having to do with memory usage  
while reading the HDF5 files.  Using HDF5 1.8 and Thomas' recent  
patch should help here.

During regridding, all time levels are changed.  Old and new time  
levels always have the same grid structure.  I don't know of any  
problems having to do with regridding and checkpointing at the same  
iteration.  I assume that this occurs naturally quite often, since  
people usually regrid and checkpoint at "even" numbers.

> I also have another question, about merging grids of the same level  
> (like in the BH mergers). How is it done in practice? All grids  
> must be rectangular, right? So are the merged grids made of  
> rectangular parts and special care is used when applying boundary  
> conditions where these parts are superposed? Or how does it work?

I assume you are speaking of combined grids which have concave  
edges.  It turns out that these faces can have neither outer nor  
symmetry boundary conditions applied.  Yes, Carpet uses special care  
for these faces.  As many grid points as possible are filled from  
neighbouring grid on the same level.  The remaining points are filled  
via interpolation from the next coarser level.

> As usual, feel free to post the reply to a list, if you find it  
> appropriate.


-erik

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

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