<div dir="ltr"><div dir="ltr">On Mon, Mar 23, 2020 at 8:41 AM Elias Karabelas <<a href="mailto:karabelaselias@gmail.com">karabelaselias@gmail.com</a>> wrote:<br></div><div class="gmail_quote"><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex">
<div>
<p>Thanks I'll have a look at it. So I understand correctly, that
purely algebraic is not the way to go through PETSc here?</p></div></blockquote><div>You can make it work. You would have the same difficulty in any linear algebra package, namely that you need</div><div>an overlapped decomposition of the matrix, which no package does by default. PETSc does it for ASM, so you could</div><div>use those routines to get what you want.</div><div><br></div><div> Thanks,</div><div><br></div><div> Matt</div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"><div><p>Cheers</p>
<p>Elias<br>
</p>
<div>On 23/03/2020 13:39, Matthew Knepley
wrote:<br>
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<blockquote type="cite">
<div dir="ltr">
<div dir="ltr">On Mon, Mar 23, 2020 at 8:38 AM Elias Karabelas
<<a href="mailto:karabelaselias@gmail.com" target="_blank">karabelaselias@gmail.com</a>>
wrote:<br>
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<p><br>
</p>
<div>On 23/03/2020 13:36, Matthew Knepley wrote:<br>
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<blockquote type="cite">
<div dir="ltr">
<div dir="ltr">On Mon, Mar 23, 2020 at 8:31 AM Elias
Karabelas <<a href="mailto:karabelaselias@gmail.com" target="_blank">karabelaselias@gmail.com</a>>
wrote:<br>
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<div class="gmail_quote">
<blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex">
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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">https://lists.mcs.anl.gov/pipermail/petsc-users/2014-August/022450.html</a></p>
<p>wondering if this would theoretically work.</p>
</div>
</blockquote>
<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>
<blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex">
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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>
</div>
</blockquote>
<div>The FEM-FCT I am familiar with from Lohner was
phrased on a mesh.</div>
</div>
</div>
</blockquote>
<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#!" target="_blank">https://www.sciencedirect.com/science/article/pii/S0045782508003150#!</a></p>
</div>
</blockquote>
<div>Volker is of course great. I believe I was thinking of <a href="https://onlinelibrary.wiley.com/doi/abs/10.1002/fld.1650071007" target="_blank">https://onlinelibrary.wiley.com/doi/abs/10.1002/fld.1650071007</a></div>
<div><br>
</div>
<div> Thanks,</div>
<div><br>
</div>
<div> Matt <br>
</div>
<blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex">
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<p>Best regards</p>
<p>Elias<br>
</p>
<p><br>
</p>
<blockquote type="cite">
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<div><br>
</div>
<div> Thanks,</div>
<div><br>
</div>
<div> Matt </div>
<blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex">
<div>
<p>Best regards</p>
<p>Elias<br>
</p>
<div>On 23/03/2020 13:02, Matthew Knepley wrote:<br>
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<blockquote type="cite">
<div dir="ltr">
<div dir="ltr">On Mon, Mar 23, 2020 at 7:46
AM Elias Karabelas <<a href="mailto:karabelaselias@gmail.com" target="_blank">karabelaselias@gmail.com</a>>
wrote:<br>
</div>
<div class="gmail_quote">
<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">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>
</blockquote>
<div><br>
</div>
<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>
</div>
<div> Thanks,</div>
<div><br>
</div>
<div> Matt</div>
<div> <br>
</div>
<blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"> Best
regards<br>
<br>
Elias<br>
<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>
<div><br>
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<div><a href="http://www.cse.buffalo.edu/~knepley/" target="_blank">https://www.cse.buffalo.edu/~knepley/</a><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>
<div><br>
</div>
<div><a href="http://www.cse.buffalo.edu/~knepley/" target="_blank">https://www.cse.buffalo.edu/~knepley/</a><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>
<div><br>
</div>
<div><a href="http://www.cse.buffalo.edu/~knepley/" target="_blank">https://www.cse.buffalo.edu/~knepley/</a><br>
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</blockquote></div><br clear="all"><div><br></div>-- <br><div dir="ltr" class="gmail_signature"><div dir="ltr"><div><div dir="ltr"><div><div dir="ltr"><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">https://www.cse.buffalo.edu/~knepley/</a><br></div></div></div></div></div></div></div></div>