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<div class="moz-cite-prefix">Le 07/12/2017 � 08:23, Mohammad Hassan
Baghaei a �crit�:<br>
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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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