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<div class="moz-cite-prefix">Le 07/12/2017 à 08:23, Mohammad Hassan
Baghaei a écrit :<br>
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cite="mid:004001d36f2c$29b9c140$7d2d43c0$@mail.sjtu.edu.cn">
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<p class="MsoNormal">Hello<o:p></o:p></p>
<p class="MsoNormal">I am using DMPlex to construct a fully
circular 2D domain for my PDEs. As I am discretizing the PDEs
using finite difference method, I need to know , to define the
layout of PetscSection, how I can find the boundary condition
IS. I know the location of the boundaries in Sieve chart.
However, I noticed that I need to know the Index Set of that
location. Can I use the Sieve point number for Index Set. It
seems I think I am not familiar with IS. Can you help me?
Thank for your help. <o:p></o:p></p>
<p class="MsoNormal">Amir<o:p></o:p></p>
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<p>Hello,</p>
<p>In snes/examples/tutorials/ex56.c you can find the following
code, which does what you want as i understood :</p>
<p>260: {<br>
261: DMLabel label;<br>
262: IS is;<br>
263: DMCreateLabel(dm, "boundary");<br>
264: DMGetLabel(dm, "boundary", &label);<br>
265: DMPlexMarkBoundaryFaces(dm, label);<br>
266: if (run_type==0) {<br>
267: DMGetStratumIS(dm, "boundary", 1, &is);<br>
268: DMCreateLabel(dm,"Faces");<br>
269: if (is) {<br>
270: PetscInt d, f, Nf;<br>
271: const PetscInt *faces;<br>
272: PetscInt csize;<br>
273: PetscSection cs;<br>
274: Vec coordinates ;<br>
275: DM cdm;<br>
276: ISGetLocalSize(is, &Nf);<br>
277: ISGetIndices(is, &faces);<br>
278: DMGetCoordinatesLocal(dm, &coordinates);<br>
279: DMGetCoordinateDM(dm, &cdm);<br>
280: DMGetDefaultSection(cdm, &cs);<br>
281: /* Check for each boundary face if any component of
its centroid is either 0.0 or 1.0 */<br>
282: for (f = 0; f < Nf; ++f) {<br>
283: PetscReal faceCoord;<br>
284: PetscInt b,v;<br>
285: PetscScalar *coords = NULL;<br>
286: PetscInt Nv;<br>
287: DMPlexVecGetClosure(cdm, cs, coordinates, faces[f],
&csize, &coords);<br>
288: Nv = csize/dim; /* Calculate mean coordinate
vector */<br>
289: for (d = 0; d < dim; ++d) {<br>
290: faceCoord = 0.0;<br>
291: for (v = 0; v < Nv; ++v) faceCoord +=
PetscRealPart(coords[v*dim+d]);<br>
292: faceCoord /= Nv;<br>
293: for (b = 0; b < 2; ++b) {<br>
294: if (PetscAbs(faceCoord - b) < PETSC_SMALL) {
/* domain have not been set yet, still [0,1]^3 */<br>
295: DMSetLabelValue(dm, "Faces", faces[f],
d*2+b+1);<br>
296: }<br>
297: }<br>
298: }<br>
299: DMPlexVecRestoreClosure(cdm, cs, coordinates,
faces[f], &csize, &coords);<br>
300: }<br>
301: ISRestoreIndices(is, &faces);<br>
302: }<br>
303: ISDestroy(&is);<br>
304: DMGetLabel(dm, "Faces", &label);<br>
305: DMPlexLabelComplete(dm, label);<br>
306: }<br>
307: }</p>
<p><br>
</p>
<p>The idea is to mark boundary faces with DMPlexMarkBoundaryFaces,
and get the IS of the labeled faces, and sort them with the
position of the centroid of the face.<br>
</p>
<p>Regards,</p>
<p>Yann<br>
</p>
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