On Mon, Jan 9, 2012 at 10:37 AM, Alexander Grayver <span dir="ltr"><<a href="mailto:agrayver@gfz-potsdam.de">agrayver@gfz-potsdam.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">
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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></div></blockquote><div><br></div><div>The size of the block being factorized by ILU(0) decreases as p increases. Thus, it is</div><div>a weaker preconditioner. I recommend Yousef Saad's book which explains all this clearly.</div>
<div><br></div><div> Matt</div><div> </div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div bgcolor="#ffffff" text="#000000">
Thanks.<br>
<br>
On 09.01.2012 17:36, Matthew Knepley wrote:
<blockquote type="cite">On Mon, Jan 9, 2012 at 10:31 AM, Alexander Grayver <span dir="ltr"><<a href="mailto:agrayver@gfz-potsdam.de" target="_blank">agrayver@gfz-potsdam.de</a>></span>
wrote:<br>
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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>
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<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>
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<div> Matt</div>
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Regards,<br>
Alexander<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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</blockquote></div><br><br clear="all"><div><br></div>-- <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>