On Wed, Feb 16, 2011 at 9:18 AM, Juha Jäykkä <span dir="ltr"><<a href="mailto:juhaj@iki.fi">juhaj@iki.fi</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;">
> SNESSolve uses a Newton method so the linear system is being solving for a<br>
<br>
So the "solution" in the KSP should actually be identically zero for a<br>
converged result?<br></blockquote><div><br></div><div>It is a correction, and the correction to the exact answer is zero.</div><div> </div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex;">
> defect. If the initial guess is zero, then it would normally pick up your<br>
> Dirichlet boundary conditions on the first iteration and all subsequent<br>
> solves would have zero in those locations.<br>
<br>
It is not zero initially. But, on the other hand, it has zeros at both ends<br>
even at the very first iteration. If I understood your reply correctly, this<br>
would be expected for an initial guess which has correct values at the<br>
boundaries and it should only pick them up on the first iteration if they were<br>
not correct to begin with.<br></blockquote><div><br></div><div>Yes.</div><div> </div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex;">
Having ruled out a possibility of a bug in KSP, I need to continue my hunt for<br>
DIVERGED_LINEAR_SOLVE... None of the convergence tolerances seem to make any<br>
difference, it always diverges. The funny thing is, it diverges even if I<br>
start with an *exact* *solution*...<br></blockquote><div><br></div><div>It is a good idea to use -ksp_type preonly -pc_type lu to start until you understand the problem.</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;">
Cheers,<br>
Juha<br>
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| Juha Jäykkä, <a href="mailto:juhaj@iki.fi">juhaj@iki.fi</a> |<br>
| <a href="http://www.maths.leeds.ac.uk/~juhaj" target="_blank">http://www.maths.leeds.ac.uk/~juhaj</a> |<br>
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</font></blockquote></div><br><br clear="all"><br>-- <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>