[Carpet] Regridding and scheduling in new version of Carpet

[Ian Hinder]

Hi,

I have a question about scheduling in the new version of Carpet.  I have
a thorn which sets up the CarpetRegrid coordinates string based on a
spherical surface.

In carpet-stable-3, I set the spherical surface in BASEGRID, and set the
coordinates string in PREREGRID.  This appears to work.

In the development version of Carpet, things have changed.  There is now
a schedule bin PREREGRIDINITIAL, and regridding now seems to happen
*before* BASEGRID.  The output from Cactus says:

  Initialisation
    [CCTK_PREREGRIDINITIAL]
    Set up grid hierarchy
    [CCTK_POSTREGRIDINITIAL]
    [CCTK_BASEGRID]
      [CCTK_INITIAL]
      Restrict from finer grids
      [CCTK_POSTRESTRICTINITIAL]
      [CCTK_POSTINITIAL]

So it seems that I have to set the coordinates string in
PREREGRIDINITIAL in order to have the grid hierarchy set up correctly
when the initial regridding happens.  However, the information required
to do this comes from a spherical surface.  I could set this spherical
surface in PREREGRIDINITIAL as well, but then it will get overwritten by
SphericalSurface_Setup which is called in BASEGRID.  Have I understood
this correctly?

The documentation in Carpet/doc/scheduling.tex says that the bins are
run in the order

    [CCTK_BASEGRID]
      [CCTK_INITIAL]
    [CCTK_PREREGRIDINITIAL]
	Regrid
    [CCTK_POSTREGRIDINITIAL]

and this seems to me to make much more sense, but I understand if it is
out of date.

As an aside, I note that CarpetTracker, which tells CarpetRegrid2 where
to put its grids based on a spherical surface, is scheduled only in
PREREGRID.  I don't see how this can work?

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