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<div class="moz-cite-prefix">On 23/03/2020 13:36, Matthew Knepley
wrote:<br>
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cite="mid:CAMYG4G=SwqVCLxCFzfFTo8M4j-AsTeDhC6Rqa8TdBYdi=QCqzA@mail.gmail.com">
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<div dir="ltr">On Mon, Mar 23, 2020 at 8:31 AM Elias Karabelas
<<a href="mailto:karabelaselias@gmail.com"
moz-do-not-send="true">karabelaselias@gmail.com</a>>
wrote:<br>
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<p>Dear Matt,</p>
<p>I've just found this answer from 2014</p>
<p><a
href="https://lists.mcs.anl.gov/pipermail/petsc-users/2014-August/022450.html"
target="_blank" moz-do-not-send="true">https://lists.mcs.anl.gov/pipermail/petsc-users/2014-August/022450.html</a></p>
<p>wondering if this would theoretically work.</p>
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<div>In serial certainly, I just don't see how it works in
parallel since you might not own the row you need from the
transpose. </div>
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<p>And the thing with this FCT-Schemes is, that they're
build on purely algebraic considerations (like AMG) so I
don't want to break it back down to mesh information if
possible at all.</p>
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<div>The FEM-FCT I am familiar with from Lohner was phrased on
a mesh.</div>
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<p>Can you give me a reference to that? I based my things on this
work <a
href="https://www.sciencedirect.com/science/article/pii/S0045782508003150#!">https://www.sciencedirect.com/science/article/pii/S0045782508003150#!</a></p>
<p>Best regards</p>
<p>Elias<br>
</p>
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<div> Thanks,</div>
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<div> Matt </div>
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<p>Best regards</p>
<p>Elias<br>
</p>
<div>On 23/03/2020 13:02, Matthew Knepley wrote:<br>
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<div dir="ltr">On Mon, Mar 23, 2020 at 7:46 AM Elias
Karabelas <<a
href="mailto:karabelaselias@gmail.com"
target="_blank" moz-do-not-send="true">karabelaselias@gmail.com</a>>
wrote:<br>
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<blockquote class="gmail_quote" style="margin:0px
0px 0px 0.8ex;border-left:1px solid
rgb(204,204,204);padding-left:1ex">Dear Users,<br>
<br>
I want to implement a FCT (flux corrected
transport) scheme with PETSc. <br>
To this end I have amongst other things create a
Matrix whose entries <br>
are given by<br>
<br>
L_ij = -max(0, A_ij, A_ji) for i neq j<br>
<br>
L_ii = Sum_{j=0,..n, j neq i} L_ij<br>
<br>
where Mat A is an (non-symmetric) Input Matrix
created beforehand.<br>
<br>
I was wondering how to do this. My first search
brought me to <br>
<a
href="https://www.mcs.anl.gov/petsc/petsc-current/src/mat/examples/tutorials/ex16.c.html"
rel="noreferrer" target="_blank"
moz-do-not-send="true">https://www.mcs.anl.gov/petsc/petsc-current/src/mat/examples/tutorials/ex16.c.html</a>
<br>
<br>
<br>
but this just goes over the rows of one matrix to
set new values and now <br>
I would need to run over the rows and columns of
the matrix. My Idea was <br>
to just create a transpose of A and do the same
but then the row-layout <br>
will be different and I can't use the same for
loop for A and AT and <br>
thus also won't be able to calculate the max's
above.<br>
<br>
Any help would be appreciated<br>
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<div><br>
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<div>I think it would likely be much easier to write
your algorithm directly on the mesh, rather than
using matrices, since the locality information is
explicit with the mesh, but has to be
reconstructed with the matrix.</div>
<div><br>
</div>
<div>The problem here is that in parallel there
would be no easy way to get the halo you need
using a matrix. You</div>
<div>really want the ghosted space for assembly, and
that is provided by the DM objects. Does this make
sense?</div>
<div>Unless anybody in PETSc has a better idea.</div>
<div><br>
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<div> Thanks,</div>
<div><br>
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<div> Matt</div>
<div> <br>
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rgb(204,204,204);padding-left:1ex"> Best regards<br>
<br>
Elias<br>
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<div>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</div>
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<div><a
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<div>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</div>
<div><br>
</div>
<div><a href="http://www.cse.buffalo.edu/~knepley/"
target="_blank" moz-do-not-send="true">https://www.cse.buffalo.edu/~knepley/</a><br>
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