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<div class="moz-cite-prefix">Jed,<br>
<br>
I do see the drawbacks of this method, but it seems to have good
scalability. <br>
That I want to test.<br>
<br>
Thank you.<br>
<br>
On 17.08.2012 16:32, Jed Brown wrote:<br>
</div>
<blockquote
cite="mid:CAM9tzSkm8T5x5=u2pha-Y83oqhmOVr6tgBm+3EmaK1onH49t3Q@mail.gmail.com"
type="cite">
<div class="gmail_quote">On Fri, Aug 17, 2012 at 9:23 AM,
Alexander Grayver <span dir="ltr"><<a moz-do-not-send="true"
href="mailto:agrayver@gfz-potsdam.de" target="_blank">agrayver@gfz-potsdam.de</a>></span>
wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0
.8ex;border-left:1px #ccc solid;padding-left:1ex">
<div bgcolor="#FFFFFF" text="#000000">Right. <br>
Could you please explain what do you mean by fragile? <br>
</div>
</blockquote>
<div><br>
</div>
<div>Fragile means unreliable. The math is not right for Krylov
methods in general. You are relying on side-effects of
particular methods and preconditioner side combinations.
Fragile is the opposite of "robust". For a "robust" method,
you should start with a compatible discretization and/or
choose a preconditioner that is stable on the quasi-null space
and/or filter in a way that is consistent with the Krylov
method (e.g. as described using FGMRES).</div>
<div> </div>
<blockquote class="gmail_quote" style="margin:0 0 0
.8ex;border-left:1px #ccc solid;padding-left:1ex">
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<div class="im">
<blockquote type="cite">
<div class="gmail_quote">
<blockquote class="gmail_quote" style="margin:0 0 0
.8ex;border-left:1px #ccc solid;padding-left:1ex">
<div bgcolor="#FFFFFF" text="#000000"> <br>
Looks a bit tricky. The number of fgmres
iterations then defines number of the cycles
correction will be applied, doesn't it?</div>
</blockquote>
<div><br>
</div>
<div>Yes.</div>
</div>
</blockquote>
<br>
</div>
If I do this command line only setup:
<div class="im"><br>
-pc_type composite -pc_composite_type multiplicative
-pc_composite_pcs ksp,shell<br>
<br>
</div>
How does petsc know what ShellPCApply routine to take? I
guess I have to specify this in the code anyway?</div>
</blockquote>
</div>
<br>
<div>Yeah, to select your preconditioner in this way, you should
name it preconditioner something meaningful and use
PCRegisterDynamic() just like the native implementations.</div>
</blockquote>
<br>
<br>
<pre class="moz-signature" cols="72">--
Regards,
Alexander</pre>
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