<html><head><meta http-equiv="Content-Type" content="text/html; charset=utf-8"></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; line-break: after-white-space;" class=""><br class=""><div><br class=""><blockquote type="cite" class=""><div class="">On May 16, 2022, at 3:50 PM, Loic Gouarin <<a href="mailto:loic.gouarin@polytechnique.edu" class="">loic.gouarin@polytechnique.edu</a>> wrote:</div><br class="Apple-interchange-newline"><div class="">
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<div text="#000000" bgcolor="#FFFFFF" class=""><p class="">Thanks Barry for your quick reply.<br class="">
</p>
<div class="moz-cite-prefix">Le 16/05/2022 à 21:41, Barry Smith a
écrit :<br class="">
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<blockquote type="cite" cite="mid:A76657E7-8E3E-419E-9831-A94A73E032AD@petsc.dev" class="">
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Loic,
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<div class=""> From your code it looks like you are using a DM.
Is it a DMDA or a shell DM? If it is a DMDA then the process is
intended to be pretty straightforward. PCTELESCOPE should create
a new DMDA that has the same properties as the coarse grid DMDA
but lives on a smaller number of ranks. From this you can just
provide multiple levels of coarsening of the DMDA to produce the
smaller multigrid problems. <br class="">
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</blockquote>
It's a DMDA. So what you mean is to take the KSP of PCTELESCOPE, get
the DM which is the same of the coarse grid and build all the levels
as previously for the levels of PCTELESCOPE ?<br class=""></div></div></blockquote><div><br class=""></div> Yes, I think you should be able to pull out of the coarse level PC (on the subset of ranks) a DM that and then setup coarse levels from that. But you need to look at an example that that uses telescope and probably even the telescope code itself to see all the details. I don't know them anymore.</div><div><br class=""></div><div> Barry</div><div><br class=""><blockquote type="cite" class=""><div class=""><div text="#000000" bgcolor="#FFFFFF" class="">
<blockquote type="cite" cite="mid:A76657E7-8E3E-419E-9831-A94A73E032AD@petsc.dev" class="">
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<div class=""> Can you let us know more details of what exactly
goes wrong with attempts? It is likely straightforward to get
things working, perhaps due to our unclear documentation.</div>
</blockquote><p class="">I essentially have wrong state or NULL matrices into the
PCTELESCOPE.</p><p class="">Loic<br class="">
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<blockquote type="cite" cite="mid:A76657E7-8E3E-419E-9831-A94A73E032AD@petsc.dev" class="">
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<div class=""> Barry</div>
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<div class="">On May 16, 2022, at 3:28 PM, Loic Gouarin <<a href="mailto:loic.gouarin@polytechnique.edu" class="moz-txt-link-freetext" moz-do-not-send="true">loic.gouarin@polytechnique.edu</a>>
wrote:</div>
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<div text="#000000" bgcolor="#FFFFFF" class=""><p class="">Hello,</p><p class="">I could have posted my message on the user
list but it seems to me that it's more in the petsc
development part. Don't hesitate to tell me if I'm
wrong.<br class="">
I am developing a code called cafes that studies
fluid-particle interactions in a Stokes fluid. For
that, we implemented the whole solver in matrix free
on a cartesian grid. The preconditioner is naturally a
geometrical multigrid for the velocity. The set of
matrix free for each level is set by hand (I worked
with Matthew on this a long time ago now!). <br class="">
I would have liked to implement telescope on this
part. I started it but I didn't get out of it. So I
would like to have your help.<br class="">
What I tried to do was to describe my classical
multigrid up to a level N1 and then take the coarse
solver and apply the telescope preconditioner to it up
to a level N2. I don't know if this is the best way
but it seemed the most intuitive. The problem is that
I could not get the coarse matrix because the setup is
not done yet (I use a DMKSPSetComputeOperators for the
matrices). <br class="">
</p><p class="">The construction of the matrix free for each
level is here:
<a class="moz-txt-link-freetext" href="https://github.com/gouarin/cafes/blob/master/cafes/problem/stokes.hpp#L59-L88" moz-do-not-send="true">https://github.com/gouarin/cafes/blob/master/cafes/problem/stokes.hpp#L59-L88</a></p><p class="">The description of the Stokes preconditioner
is described here :
<a class="moz-txt-link-freetext" href="https://github.com/gouarin/cafes/blob/master/cafes/problem/stokes.hpp#L109-L162" moz-do-not-send="true">https://github.com/gouarin/cafes/blob/master/cafes/problem/stokes.hpp#L109-L162</a></p><p class="">I have tried multiple implementations
without success. For me, the start is to add at line
105 something like</p>
<div style="color: #d4d4d4;background-color: #1e1e1e;font-family: Menlo, Monaco, 'Courier New', monospace;font-weight: normal;font-size: 12px;line-height: 18px;white-space: pre;" class=""><div class=""><span style="color: #57a64a;" class="">KSP coarse;</span></div><div class=""><span style="color: #57a64a;" class="">ierr = PCMGGetCoarseSolve(pc_i, &coarse);CHKERRQ(ierr);</span></div><span style="color: #57a64a;" class="">
</span></div>
<div style="color: #d4d4d4;background-color: #1e1e1e;font-family: Menlo, Monaco, 'Courier New', monospace;font-weight: normal;font-size: 12px;line-height: 18px;white-space: pre;" class=""><span style="color: #57a64a;" class="">PC pc_coarse;</span><div class=""><span style="color: #57a64a;" class="">ierr = KSPGetPC(coarse, &pc_coarse);CHKERRQ(ierr);</span></div><div class=""><span style="color: #57a64a;" class="">ierr = PCSetType(pc_coarse, PCTELESCOPE);CHKERRQ(ierr);</span></div></div>
<div class=""><span style="color: #57a64a;" class=""><br class="">
</span></div>
<div class="">Then, to create the several matrices of
the levels of TELESCOPE, I thought using the same
process as before with DMKSPSetComputeOperators. But
it doesn't work...<br class="">
</div>
<div class="">Could you tell me how I can make it work ?</div>
<div class=""><br class="">
</div>
<div class="">Thanks,</div>
<div class="">Loic<br class="">
</div>
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