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<div class="moz-cite-prefix">Am 24.10.2012 21:33, schrieb Matthew
Knepley:<br>
</div>
<blockquote
cite="mid:CAMYG4G=pHtpz4dyF17-Z7rMGuj6pEYDqYr_b3RZ8rVDprACo-w@mail.gmail.com"
type="cite">On Wed, Oct 24, 2012 at 3:23 PM, Thomas Witkowski <span
dir="ltr"><<a moz-do-not-send="true"
href="mailto:thomas.witkowski@tu-dresden.de" target="_blank">thomas.witkowski@tu-dresden.de</a>></span>
wrote:<br>
<div class="gmail_quote">
<blockquote class="gmail_quote" style="margin:0 0 0
.8ex;border-left:1px #ccc solid;padding-left:1ex">
I want to play around with some special type of a Schur
complement preconditioner. It perfectly fits into PETSc's
fieldsplit preconditioner (schur - full factorization). But
for the inner solvers, I would like to create some MatShells.
So I need to access both KSP objects, for the upper block
(KSP(A_00)) and for the Schur complement (KSP(S)). How can I
get these objects in my source code?<br>
</blockquote>
<div><br>
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<div>First you have to make them different. This happens when
you give options for</div>
<div><br>
</div>
<div> -fieldsplit_1_upper_*</div>
<div> -fieldsplit_1_inner_*</div>
<div><br>
</div>
<div>This is how I customize the solvers to get things like
SIMPLE. Once they are created, you</div>
<div>can get them by pulling apart the FS. The upper is
fs->kspupper, and the inner is the KSP</div>
<div>from the MATSCHUR from fs->schur.</div>
</div>
</blockquote>
I don't understand your solution. Maybe I should put some lines of
code to emphasize my question. The relevant part looks as follows:<br>
<br>
PCSetType(pc, PCFIELDSPLIT);<br>
PCFieldSplitSetSchurFactType(pc, PC_FIELDSPLIT_SCHUR_FACT_FULL);<br>
...<br>
PCFieldSplitSetIS(pc, "velocity", is0);<br>
PCFieldSplitSetIS(pc, "pressure", is1);<br>
...<br>
KSP velocity;<br>
KSP schur;<br>
....<br>
<br>
Okay, I don't solve any Stokes/Navier Stokes equation, but to make
the names somehow convenient I choose here the names velocity and
pressure for the two system blocks. My question is now, how to
figure out the two inner solver objects from the field split
preconditioner. <br>
<br>
Matt, if your answer is still appropriate to my question, can you
make it clear on the above piece of code? Thank you very much.<br>
<br>
Thomas<br>
<br>
<blockquote
cite="mid:CAMYG4G=pHtpz4dyF17-Z7rMGuj6pEYDqYr_b3RZ8rVDprACo-w@mail.gmail.com"
type="cite">
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<div><br>
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<div> Matt</div>
<div> </div>
<blockquote class="gmail_quote" style="margin:0 0 0
.8ex;border-left:1px #ccc solid;padding-left:1ex">
Best regards,<br>
<br>
Thomas<br>
</blockquote>
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<div><br>
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-- <br>
What most experimenters take for granted before they begin their
experiments is infinitely more interesting than any results to
which their experiments lead.<br>
-- Norbert Wiener<br>
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