[Users] normal vector when looping over boundary using CCTK_LOOP3_BND

[Erik Schnetter]

It is supposed to be negative at lower boundaries. Sign error?

-erik

On Thu, May 7, 2020 at 02:42 Roland Haas <rhaas at illinois.edu> wrote:

> Hello all,
>
> I am trying to loop over the boundary of my domain using
> CCTK_LOOP3_BND(cckGH, i,j,k, ni,nj,nk). The documentation
> http://einsteintoolkit.org/usersguide/UsersGuidech9.html#x13-102000C1.7.1
> says that "ni, nj, and nk are names of variables describing the
> (outwards pointing) normal direction to the boundary as well as the
> distance to the boundary."
>
> However on a 5x5x5 grid and 1 boundary point in a uniprocess setup ni,
> nj, nk are either 0 or 1 but never eg -1 which I would expect for the
> lower boundary.
>
> Looking at the code in flesh/src/include/cctk_Loop.h shows that ni is
> computed as
>
> const int ni CCTK_ATTRIBUTE_UNUSED = cctki0_idir<0 ? i+1 : cctki0_idir==0
> ? 0 : cctki0_imax-i;
>
> ie by construction is always non-negative. LoopControl does the same.
>
> Now my question is how am I supposed to find out which boundary I am
> at (lower or upper)?
>
> Yours,
> Roland
>
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-- 
Erik Schnetter <schnetter at cct.lsu.edu>
http://www.perimeterinstitute.ca/personal/eschnetter/
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