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Il 14/05/24 15: 02, Matthew Knepley ha scritto: On Tue, May 14, 2024 at 12: 14 AM Matteo Semplice <matteo. semplice@ uninsubria. it> wrote: Dear petsc-users, I am playing with DMPlexGetCellCoordinates and observing that it returns correct
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<div class="moz-cite-prefix">Il 14/05/24 15:02, Matthew Knepley ha
scritto:<br>
</div>
<blockquote type="cite" cite="mid:CAMYG4G=kpMYw8LGxx63SmbpPN_PhswmDZJV84kU2Te3p_LCfZw@mail.gmail.com">
<div dir="ltr">
<div dir="ltr">On Tue, May 14, 2024 at 12:14 AM Matteo Semplice
<<a href="mailto:matteo.semplice@uninsubria.it" moz-do-not-send="true" class="moz-txt-link-freetext">matteo.semplice@uninsubria.it</a>>
wrote:<br>
</div>
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<div style="font-size:1px;color:rgb(255,255,255);line-height:1px;height:0px;max-height:0px;opacity:0;overflow:hidden;display:none">
Dear petsc-users, I am playing with
DMPlexGetCellCoordinates and observing that it returns
correct periodic coordinates for cells, but not for
faces. More precisely, adding
PetscCall(DMPlexGetHeightStratum(dm, 1, &fStart,
&fEnd)); for
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<p>Dear petsc-users,</p>
<p> I am playing with DMPlexGetCellCoordinates and
observing that it returns correct periodic coordinates
for cells, but not for faces.</p>
<p>More precisely, adding <br>
</p>
<p> <font face="monospace">PetscCall(DMPlexGetHeightStratum(dm,
1, &fStart, &fEnd));<br>
for (f = fStart; f < fEnd; ++f) {<br>
const PetscScalar *array;<br>
PetscScalar *x = NULL;<br>
PetscInt ndof;<br>
PetscBool isDG;<br>
<br>
PetscCall(DMPlexGetCellCoordinates(dm, f,
&isDG, &ndof, &array, &x));<br>
PetscCheck(ndof % cdim == 0, PETSC_COMM_SELF,
PETSC_ERR_ARG_INCOMP, "ndof not divisible by cdim");<br>
PetscCall(PetscPrintf(PETSC_COMM_SELF, "Face
#%" PetscInt_FMT " coordinates\n", f - fStart));<br>
for (PetscInt i = 0; i < ndof; i += cdim)
PetscCall(PetscScalarView(cdim, &x[i],
PETSC_VIEWER_STDOUT_SELF));<br>
PetscCall(DMPlexRestoreCellCoordinates(dm, f,
&isDG, &ndof, &array, &x));<br>
}</font><br>
</p>
<p>to src/dm/impls/plex/tutorials/ex8.c, I get <font face="monospace"><br>
</font></p>
<p><font face="monospace">$ ./ex8 -dm_plex_dim 2
-petscspace_degree 1 -dm_plex_simplex 0
-dm_plex_box_faces 3,2 -dm_plex_box_bd periodic,none
-dm_view -view_coord <br>
DM Object: box 1 MPI process<br>
type: plex<br>
box in 2 dimensions:<br>
Number of 0-cells per rank: 9<br>
Number of 1-cells per rank: 15<br>
Number of 2-cells per rank: 6<br>
Periodic mesh (PERIODIC, NONE) coordinates localized<br>
</font></p>
<p><font face="monospace">[...]</font></p>
<p><font face="monospace">Element #2 coordinates<br>
0: 6.6667e-01 0.0000e+00<br>
<font color="#26a269"> 0: 1.0000e+00 0.0000e+00
<<<----- correct<br>
0: 1.0000e+00 5.0000e-01</font><br>
0: 6.6667e-01 5.0000e-01<br>
[...]</font></p>
<p><font face="monospace">Face #0 coordinates<br>
0: 0.0000e+00 0.0000e+00<br>
0: 3.3333e-01 0.0000e+00<br>
Face #1 coordinates<br>
0: 3.3333e-01 0.0000e+00<br>
0: 6.6667e-01 0.0000e+00<br>
Face #2 coordinates<br>
<font color="#a51d2d"> 0: 6.6667e-01 0.0000e+00<br>
0: 0.0000e+00 0.0000e+00 <<<----
should be (0.66,0.00) and (1.00,0.00)<br>
</font></font></p>
<p>Is there a way to recover correct periodic
coordinates in the case of periodic DMPLex?</p>
</div>
</div>
</blockquote>
<div>The way that periodic coordinates work is that it stores
a DG coordinate field by cell. Faces default back to the
vertices. You could think about also putting DG coordinates
on faces, but no one had asked, and it is potentially
expensive.</div>
<div><br>
</div>
<div>If you really need them to keep going, face coordinates
can be extracted from cell coordinates. Otherwise, I can do
it after the PETSc Meeting. Or, we are happy to take
contributions adding this.</div>
</div>
</div>
</blockquote>
<p>Hi.</p>
<p>I mainly wanted to check that this was expected and not a result
of a setup of my DM. No need to change Petsc now except maybe
issuing a warning if the fallback to continuous coordinates will
give wrong results. As for my code, I think I can extract the info
from the cell coordinates in a pre-processing phase and if this
crazy FV methods I am implementing will survive for long enough,
I'll think about contributing.<br>
</p>
<p>Just to double-check, can I assume that the order in which <font face="monospace">DMPlexGetCellCoordinates</font> returns the
coordinates matches the ordering of vertices in DMPlexGetCone for
the uninterpolated DM, right?<br>
</p>
<p>Best</p>
<p> Matteo<br>
</p>
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