[Users] problem with GenericFD

[Erik Schnetter]

On Thu, Mar 1, 2012 at 4:14 PM, Bruno Giacomazzo
<bruno.giacomazzo at jila.colorado.edu> wrote:
> Hi Roland,
> thanks for the prompt reply.
>
> On Mar 1, 2012, at 12:46 PM, Roland Haas wrote:
>
> # Parameters of thorn CoordBase (implementing CoordBase)
>
> CoordBase::boundary_shiftout_x_lower = 1
>
> CoordBase::boundary_shiftout_z_lower = 1
>
> CoordBase::boundary_size_x_lower     = 3
>
> CoordBase::boundary_size_z_lower     = 3
>
> Maybe
> CoordBase::boundary_size_y_lower     = 3
> CoordBase::boundary_size_x_upper     = 3
> CoordBase::boundary_size_y_upper     = 3
> CoordBase::boundary_size_z_upper     = 3
> are missing? I certainly use those.
>
>
> this fixed the problem.
>
> In the past I never used the *_upper and I used the*_ lower only for those
> directions where I was applying a symmetry condition. I think the *_upper
> just extends the grid from xmax to xmax+3*dx, while without them the
> boundary points are included in xmax. I'm not sure what is the effect of
> having added also y_lower, but the initial data look correct as before.

This parameter specifies to other thorns (including Carpet) how many
boundary zones there are, as explained by Ian.

If you don't want the grid to become larger in these directions, you
can set these to "inner" boundaries, which means that the boundary
zones don't get added to the outside, but rather "relabel" grid points
that would otherwise be interior grid points. Both are consistent; the
difference in only where the boundary grid points are located with
respect to the physical outer boundary. You can also use the shiftout
parameters to move the boundary points with a similar effect.

On symmetry boundaries, you need to use "outer" boundaries and a
"shiftout" of 1 (for vertex centering), as you already do. But you are
free to specify anything on other boundaries.

-erik

-- 
Erik Schnetter <schnetter at cct.lsu.edu>
http://www.perimeterinstitute.ca/personal/eschnetter/