Cactus Code Thorn Boundary
Authors: Gabrielle Allen, Gerd Lanfermann, Miguel Alcubierre
CVS info   : $Header$
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1. Purpose of the thorn

This thorn provides some standard outer boundary conditions. 

Currently:

  - flat boundary conditions (a copy of the point just inside the
    boundary)
 
  - radiation boundary conditions

2. Additional information

This thorn only currently works with a 3D Cartesian Grid
The boundary conditions can be called from Fortran or C, 
and can be passed either groups of grid functions, or single
grid variables.
The flat boundary conditions work with any size stencil width,
the radiation boundary conditions only currently work with 
a stencil width of one.

To apply a flat boundary condition from Fortran

	call ApplyFlatBC(cctkGH,sw,"imp::group_or_var")

to apply a radiative boundary condition from Fortran

	call ApplyRadiativeBC(cctkGH,num,sw,"imp::group_or_var","imp::group_or_var2")

Where:
 stencil width is a dimension 3 integer array containing the stencil 
 width in each direction
 num is a coefficient in the implemented radiative boundary condition
 that is usually one. 

See the documentation for more details.