[Carpet] Proper nesting

[Ian Hinder]

Erik Schnetter wrote:
> 
> On Apr 3, 2008, at 12:35:33, Ian Hinder wrote:
>> Now, it looks like CarpetRegrid2 (which I am not using) claims to
>> "enforce" proper nesting.  To do this, it seems to work from the coarse
>> grids to the fine ones, and for each grid, it works out whether the
>> current grid would need to be enlarged to contain the next finest one.
>> It then enlarges it if necessary, and then goes to the next finest and
>> repeats.  Is this roughly right?
> 
> This is right, except that it works from finest to coarsest grid.  There

Ah I misread the loop - you are right.

>>  Is this procedure supposed to ensure
>> proper nesting, in the sense that no points are used for prolongation
>> that are themselves prolongated?
> 
> Yes.  In addition, it also requires a certain distance between the
> boundaries of fine and coarse grids, i.e., a certain number of grid
> points which are neither interpolated from the next coarser nor serve to
> interpolate to the next finer grid.
> 
>> How can it do this if it doesn't know
>> about the number of buffer zones, which are only added later in the
>> routine?
> 
> ?
> 
> It should know about the buffer zones.  Maybe there is an error...

No - my mistake again.  Now that I see that the loop is traversed fine
to coarse, it makes sense that the current level is enlarged to contain
the next finest one, which has already been itself enlarged, and then
buffer zones are added to the current level, so that when the next
coarsest is computed, it sees the buffer zones from the current one.

-- 
Ian Hinder
hinder at gravity.psu.edu
http://www.gravity.psu.edu/~hinder