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I see this is due to preconditioner, but could you explain shortly
what particularly causes this problem? It's not obvious to me.<br>
<br>
Thanks.<br>
<br>
On 09.01.2012 17:36, Matthew Knepley wrote:
<blockquote
cite="mid:CAMYG4G=Fvn36637rpQKxMbLMBkhtLZK1qvuTF8CZ8mEpLa8OZA@mail.gmail.com"
type="cite">On Mon, Jan 9, 2012 at 10:31 AM, Alexander Grayver <span
dir="ltr"><<a moz-do-not-send="true"
href="mailto:agrayver@gfz-potsdam.de">agrayver@gfz-potsdam.de</a>></span>
wrote:<br>
<div class="gmail_quote">
<blockquote class="gmail_quote" style="margin: 0pt 0pt 0pt
0.8ex; border-left: 1px solid rgb(204, 204, 204);
padding-left: 1ex;">
I have tested default GMRES+ILU(0) solver for problem of size
~200000 and I observed that both convergence rate and accuracy
degrade when I increase number of processes.<br>
E.g., number of iterations almost doubles when going from 1 to
4 processors.<br>
<br>
I noticed that ILU(0) is somehow represented by sequential
matrices internally and feel that this might be a reason?<br>
</blockquote>
<div><br>
</div>
<div>The default is Block Jacobi+ILU(0) and GMRES(30) which will
definitely degrade as the number of</div>
<div>processes is increased. You would need to use an optimal
preconditioner like Multigrid if you want</div>
<div>a constant number of iterates.</div>
<div><br>
</div>
<div> Matt</div>
<div> </div>
<blockquote class="gmail_quote" style="margin: 0pt 0pt 0pt
0.8ex; border-left: 1px solid rgb(204, 204, 204);
padding-left: 1ex;">
Regards,<br>
Alexander<br>
</blockquote>
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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>
</blockquote>
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