<div dir="ltr"><div class="gmail_extra"><div class="gmail_quote">On Wed, Mar 26, 2014 at 7:54 PM, TAY wee-beng <span dir="ltr"><<a href="mailto:zonexo@gmail.com" target="_blank">zonexo@gmail.com</a>></span> wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
<div text="#000000" bgcolor="#FFFFFF">
<div>On 27/3/2014 12:14 AM, Matthew Knepley
wrote:<br>
</div>
<blockquote type="cite">
<div dir="ltr">
<div class="gmail_extra">
<div class="gmail_quote">On Wed, Mar 26, 2014 at 10:42 AM, TAY
wee-beng <span dir="ltr"><<a href="mailto:zonexo@gmail.com" target="_blank">zonexo@gmail.com</a>></span>
wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
<div text="#000000" bgcolor="#FFFFFF">
<div>On 26/3/2014 11:22 PM, Matthew Knepley wrote:<br>
</div>
<blockquote type="cite">
<div dir="ltr">
<div class="gmail_extra">
<div class="gmail_quote">On Wed, Mar 26, 2014 at
9:59 AM, TAY wee-beng <span dir="ltr"><<a href="mailto:zonexo@gmail.com" target="_blank">zonexo@gmail.com</a>></span>
wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">Hi,<br>
<br>
I am running a CFD solver. The Poisson eqn was
originally solved using HYPRE's geometric
multigrid.<br>
</blockquote>
<div><br>
</div>
<div>Is this on a structured grid?</div>
</div>
</div>
</div>
</blockquote>
<br>
Yes.<br>
</div>
</blockquote>
<div><br>
</div>
<div>Then you can replicate the Hypre structured MG with the
PCMG, and it can be lighter memory than GAMG. You</div>
<div>will need to code the problem in the style of SNES ex5,
which is a Poisson for which geometric MG works from</div>
<div>the command line.</div>
<div><br>
</div>
<div> Thanks,</div>
<div><br>
</div>
<div> Matt</div>
</div>
</div>
</div>
</blockquote>
Hi Matt,<br>
<br>
First of all, is there an easier way out? Is it Boomeramg or GMRES
which has a large memory requirement? Will changing e.g. GMRES to
FGMRES or other ksp solvers solve the problem?<br></div></blockquote><div><br></div><div>You could perhaps use a low-memory Krylov method, like BiCGStab. How big is your Krylov space?</div><div> </div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
<div text="#000000" bgcolor="#FFFFFF">
Also, I switched from geometric multigrid (GMG) to Boomeramg because
the latter is faster. If I use PCMG, am I going back to the GMG
path, which was slower?<br></div></blockquote><div><br></div><div>If multigrid is working correctly, it should take 10 iterates or so. I am guessing something was wrong with the GMG, like coarse</div><div>BC.</div><div>
<br></div><div> Thanks,</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 text="#000000" bgcolor="#FFFFFF">
Thanks!<br>
<blockquote type="cite">
<div dir="ltr">
<div class="gmail_extra">
<div class="gmail_quote">
<div> </div>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
<div text="#000000" bgcolor="#FFFFFF">
<blockquote type="cite">
<div dir="ltr">
<div class="gmail_extra">
<div class="gmail_quote">
<div> Matt</div>
<div> </div>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"> Recently, I tested it
with Boomeramg as the preconditioner and GMRES
as the ksp solver. There's a 20% increase in
speed.<br>
<br>
However, when I increased the grid resolution,
I got the out of memory error. Changing the
solver back to HYPRE solved the problem.<br>
<br>
So does GMRES + Boomeramg used more memory
than other solvers? Are there alternatives?<br>
<br>
Thank you.<span><font color="#888888"><span><font color="#888888"><br>
<br>
-- <br>
Yours sincerely,<br>
<br>
TAY wee-beng<br>
<br>
</font></span></font></span></blockquote>
<span><font color="#888888"> </font></span></div>
<span><font color="#888888"> <br>
<br clear="all"><span class="HOEnZb"><font color="#888888">
<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 </font></span></font></span></div><span class="HOEnZb"><font color="#888888">
</font></span></div><span class="HOEnZb"><font color="#888888">
</font></span></blockquote><span class="HOEnZb"><font color="#888888">
<br>
</font></span></div><span class="HOEnZb"><font color="#888888">
</font></span></blockquote><span class="HOEnZb"><font color="#888888">
</font></span></div><span class="HOEnZb"><font color="#888888">
<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
</font></span></div>
</div>
</blockquote>
<br>
</div>
</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
</div></div>