[Carpet] Prolongation order

[Ian Hinder]

Erik Schnetter wrote:
> On Apr 3, 2008, at 10:28:02, Ian Hinder wrote:
>> But from your description above, I would have thought the number of
>> ghost zones required would be 2 for the 5th order stencil, but
>> (prolongation_order_space+1)/2 gives 3?
> 
> A 5th order stencil (where "5" is counted according to Carpet
> conventions) requires 6 points, hence 3 the stencil radius is 3.

o o o o o o o o o o o o o o o o o
              |
X  (X) (X) (X) (X) (X) (X)  X   X

So in principle, Carpet picks one of the adjacent coarse points to the
fine point it wants to interpolate, and identifies which processor it is
on.  That processor is then asked to interpolate, which requires it to
have all six points, meaning that at least in one of the directions,
three additional points are required.  OK - getting clearer!

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