[Users] CarpetRegrid2 grid structure inconsistencies

[Erik Schnetter]

Some time ago, someone (can't find the email right now) reported
problems with CarpetRegrid2, where the grid structure may be
inconsistent. I have restructured the code, but since this is a fairly
invasive change I would like this to be thoroughly tested before
committing it.

This change may lead to Carpet using a (slightly) different grid
structure than before. The differences are not "important"; what
potentially changes is the order in which consistency conditions are
applied. I expect that, in most cases, there will be no differences.
The list of consistency conditions is:

- ensure proper nesting (level must be larger than next finer level)
- add buffer zones (only once, not really a consistency condition)
- combine regions into a single box (if this is efficient)
- apply rotating 90/180 symmetry (if requested)
- clip at outer boundary (so that boxes that are too large or are
outside are cut off)

I have uploaded the patch to the Einstein Toolkit TRAC at
<https://trac.einsteintoolkit.org/ticket/442>.

-erik

-- 
Erik Schnetter <schnetter at cct.lsu.edu>   http://www.cct.lsu.edu/~eschnett/