[Users] Carpet: using baseextents?

[Erik Schnetter]

On 2013-09-12, at 20:57 , Scott Hawley <scott.hawley at belmont.edu> wrote:

>  Goal: I'm trying to determine if a given (fine) grid vertex coincides
> with a coarser grid point.
> 
> Frank pointed me to baseextents, and I've come up with the following
> snippet of code...
> Just posting this for a sanity check: Am I on the right track?
> Is there a more robust way one should do this?
> 
> My code relies on "baseextents" being the "full" extent of a given
> refinement level, apart from any domain decomposition that occurs when
> running with multiple MPI processors.   (Well, and it relies on the fact
> that fine grid boundaries must lie along coarse grid points.)

The parenthesized remark doesn't sound quite right. See below, coarse_ilo.

> BEGIN_MAP_LOOP (cctkGH, CCTK_GF) {
>         BEGIN_LOCAL_COMPONENT_LOOP (cctkGH, CCTK_GF) {
> 
>            DECLARE_CCTK_ARGUMENTS;
> 
>            assert (maps == 1);
>            int const m = 0;            // <--- Really?  m is never > 0?

You are using "m" for two things. One of these should rather be called "ml", a "multigrid-level" that is currently unused, and is thus always 0. The other is the "map", i.e. the patch number; this is 0 unless you have multiple patches.

>            assert (mglevels == 1);
>            int const rl = reflevel;
> 
>            ivect const ilo  = vhh.at(m)->baseextents.at(m).at(rl).lower();

The second .at(m) should be .at(ml) instead.

>            ivect const istr = vhh.at(m)->baseextents.at(m).at(rl).stride();

Same here.

>            int ref_ratio = 2;         // <-- Do we support refinement ratios > 2?

Nothing uses this at the moment; it is untested and thus likely not working.

>            ivect coarse_str = istr * ref_ratio;

Better: vhh.at(ml)->baseextents.at(m).at(rl-1).stride();

Also: coarse_ilo = vhh.at(m)->baseextents.at(ml).at(rl-1).lower();

>            for (CCTK_INT k = 0 ; k < cctk_lsh[2] ; k=k+1) {
>                for (CCTK_INT j = 0 ; j < cctk_lsh[1] ; j=j+1) {
>                    for (CCTK_INT i = 0 ; i < cctk_lsh[0] ; i=i+1) {
> 
>                       // does this vertex coincide with a coarser grid vertex?
>                       if (  ( 0 ==  (i - ilo[0]) % coarse_str[0]) &&
>                             ( 0 ==  (j - ilo[1]) % coarse_str[1]) &&
>                             ( 0 ==  (k - ilo[2]) % coarse_str[2])) {

This doesn't seem quite right. ilo[0] is not in the same "units" as i; instead, it is in the same "units" as str.

Alternatively: Check whether the equation   ilo[0] + i * str[0] == coarse_ilo[0] + coarse_i * coarse_str[0]   can be solved for coarse_i, i.e. check whether

(ilo[0] + i * str[0] - coarse_ilo[0]) % coarse_str[0] == 0

and similarly for the other two directions.

>                               CCTK_VInfo(CCTK_THORNSTRING,"   We are over
> a CG vertex!");
>                       }
> 
>                    } // end loop over i
>                 } // end loop over j
>             } // end loop over k
> 
>         } END_LOCAL_COMPONENT_LOOP;
>   } END_MAP_LOOP;
> 
> 
> Thank you very much,


To test this, you can output the coordinate of the current grid point, and then check (manually) whether this coordinate exists on the next coarser grid.

-erik

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

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