[Users] boundary conditions with Llama
Erik Schnetter
schnetter at cct.lsu.edu
Tue Jun 25 13:59:19 CDT 2019
Miguel
I do not know what you see, thus I cannot comment. Can you post your
output/results somewhere, e.g. on "gist.github.com"?
-erik
On Tue, Jun 25, 2019 at 2:53 PM Miguel Zilhão
<miguel.zilhao.nogueira at tecnico.ulisboa.pt> wrote:
>
> hi all,
>
> thanks for your replies. i will try to implement something based on these suggestions. in any case
> though, it still seems to me that the behaviour of the Sn function from the Interpolate2 thorn is
> not the expected one...
>
> i understand that some points can be both "outer boundary" and "inter-process boundary", but when
> using an outer radius of 128, i wouldn't expect a point at radius~60 to ever be flagged as "outer
> boundary"... yet, this does happen for some of the tests that i've performed. if this is indeed the
> expected behaviour, maybe some clarification could be added to its interface.ccl, or documentation?
>
> thanks,
> Miguel
>
>
> On 25/06/19 15:24, Erik Schnetter wrote:
> > Miguel
> >
> > Grid functions have edges and corners, and thus there are points that
> > are both "outer boundary" and "inter-process boundary".
> >
> > The canonical way to find out where the outer boundaries are is to call
> >
> > # The location of the boundary points
> > CCTK_INT FUNCTION MultiPatch_GetBoundarySpecification \
> > (CCTK_INT IN map, \
> > CCTK_INT IN size, \
> > CCTK_INT OUT ARRAY nboundaryzones, \
> > CCTK_INT OUT ARRAY is_internal, \
> > CCTK_INT OUT ARRAY is_staggered, \
> > CCTK_INT OUT ARRAY shiftout)
> >
> > This specifies, for a given map, how many boundary points there are
> > (nboundaryzones).
> >
> > You also call
> >
> > CCTK_INT FUNCTION \
> > MultiPatch_GetBbox \
> > (CCTK_POINTER_TO_CONST IN cctkGH, \
> > CCTK_INT IN size, \
> > CCTK_INT OUT ARRAY bbox)
> >
> > to find out whether each of the 6 boundaries are outer boundaries.
> > "Outer boundary" here means that you need to apply an outer boundary
> > condition. Note that this might include some ghost zones. Depending on
> > your setup, you can either synchronize before applying outer boundary
> > conditions, and then apply them on ghost zones as well, or you can
> > skip applying outer boundary conditions on outer boundary points that
> > are ghost points, and then synchronize later.
> >
> > To find out which points are ghost points, look at cctk_bbox in cctkGH.
> >
> > -erik
> >
> >
> > On Tue, Jun 25, 2019 at 9:50 AM Haas, Roland <rhaas at illinois.edu> wrote:
> >>
> >> Hello Miguel,
> >>
> >> the official way would be to use CoordBase's GetBoundarySizesAndTypes
> >> function or replicate the code in repos/mclachlan/ML_BSSN/src/Kranc.cc,
> >> specifically GetBoundaryInfo.
> >>
> >> The repsonses in the is_symbnd from GetBoundarySizesAndTypes and
> >> GetBoundaryInfo likely differ since the former does not know about Llama so will classify Llama's inter-patch boundaries as "symmetry" boundaries while the latter does not do so.
> >>
> >> Their answer's for physical boundaries (which may not quite be the same
> >> as "outer" boundaries if symmetry boundaries count as "outer") should
> >> be identical though. And you are looking for the physical boundaries
> >> after all.
> >>
> >> Yours,
> >> Roland
> >>
> >>> hi Roland, all,
> >>>
> >>> i'm coming back to this point since i'm now realizing that my interpretation was not correct... just to recall, i'm imposing boundary conditions in the following fashion:
> >>>
> >>> reflevel = GetRefinementLevel(cctkGH)
> >>> map = MultiPatch_GetMap(cctkGH)
> >>> if (reflevel /= 0 .or. map == 0) return
> >>>
> >>> do j = 1, cctk_lsh(2)
> >>> do i = 1, cctk_lsh(1)
> >>> do k = cctk_lsh(3)-cctk_nghostzones(3)+1, cctk_lsh(3)
> >>> if (Sn(i,j,k) == -2) then
> >>>
> >>> [my BCs go here]
> >>>
> >>> end if
> >>> end do
> >>> end do
> >>> end do
> >>>
> >>> and my assumption was that the line "if (Sn(i,j,k) == -2)" would guarantee that this would only run in the physical boundary region, as per the comment in the file interface.ccl from llama/Interpolate2:
> >>>
> >>> CCTK_INT source_patch TYPE=gf TAGS='Checkpoint="no" Prolongation="none"'
> >>> {
> >>> Sn
> >>> } "source patch number, -1 for interior points, -2 for outer boundary points, -3 for inter-
> >>> processor ghost points"
> >>>
> >>> this interpretation was consistent with what it's done in the thorn LlamaWaveToy (where the BC are imposed in a similar way).
> >>>
> >>> however, when running with several processors, it seems that there are some inter-processor points marked with Sn = -2, and therefore the loop above is called outside my physical boundary region (i noticed this by adding write statements inside the loop above).
> >>>
> >>> so i have the following questions:
> >>>
> >>> - what exactly does "outer boundary points" mean for the Sn function? is there a bug, or did i just misinterpreted that "outer boundary" means the "physical" boundary?
> >>>
> >>> - what would be the canonical way of checking whether a point belongs to the physical outer boundary (ie, where BCs should be specified) when using Llama?
> >>>
> >>> thanks,
> >>> Miguel
> >>>
> >>>
> >>> On 18/06/19 16:00, Haas, Roland wrote:
> >>>> Hello Miguel,
> >>>>
> >>>>> oh, but won't this be handled by the
> >>>>>
> >>>>> if (Sn(i,j,k) == -2)
> >>>>>
> >>>>> line above?
> >>>> I see. I had no idea that this is what the grid function does.
> >>>>
> >>>>> from the description of the Sn function in the Interpolate2 thorn:
> >>>>>
> >>>>> CCTK_INT source_patch TYPE=gf TAGS='Checkpoint="no"
> >>>>> Prolongation="none"' {
> >>>>> Sn
> >>>>> } "source patch number, -1 for interior points, -2 for outer
> >>>>> boundary points, -3 for inter- processor ghost points"
> >>>>>
> >>>>> and also from the way this is done in LlamaWaveToy, i was assuming
> >>>>> that Sn(i,j,k) == -2 would guarantee that the points belong to the
> >>>>> outer boundary (ie, points where i want to specify a physical
> >>>>> boundary condition). is this assumption not correct?
> >>>> Yes, in that case this should work fine. In fact it is probably more
> >>>> correct then what I did b/c due to the way Llama works may suggestion
> >>>> would likely have treated the inter-patch bondaries in Llama as outer
> >>>> boundaries (since they are "symmetry" boundaries to Cactus).
> >>>>
> >>>> So you should be fine actually.
> >>>>
> >>>> Yours,
> >>>> Roland
> >>>>
> >>
> >>
> >>
> >> --
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> >
> >
--
Erik Schnetter <schnetter at cct.lsu.edu>
http://www.perimeterinstitute.ca/personal/eschnetter/
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