Cactus Code Thorn CarpetXRegrid
Author(s)    : Steven R. Brandt <sbrandt@cct.lsu.edu>
Maintainer(s): Steven R. Brandt <sbrandt@cct.lsu.edu>
Licence      : LGPL
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1. Purpose

Provide an extra grid function, "regrid_error," to the CarpetX driver.
This grid function is used by CarpetX and AMReX to determine where to
refine the grid.