One more ask, :-)<br><br>Which one is more efficient, richardson, preonly or no difference, if I am going to use direct solver for many times steps. <br><br>Thanks,<br><br>Yan<br><br><div class="gmail_quote">On Tue, Apr 5, 2011 at 11:06 PM, Barry Smith <span dir="ltr"><<a href="mailto:bsmith@mcs.anl.gov">bsmith@mcs.anl.gov</a>></span> wrote:<br>
<blockquote class="gmail_quote" style="margin: 0pt 0pt 0pt 0.8ex; border-left: 1px solid rgb(204, 204, 204); padding-left: 1ex;"><div><div></div><div class="h5"><br>
On Apr 5, 2011, at 9:52 PM, Ryan Yan wrote:<br>
<br>
> Hi,<br>
> I am wondering is there a way of checking the residual of a direct solver. It should<br>
> be one shot and very small. I tried -ksp_monitor_true_residual, but no thing shows up. I guess a piece of code<br>
> $Ax-b$ will do the trick?<br>
<br>
</div></div> The reason that the monitor doesn't display anything is not the direct solver but because you are using LU with KSPType of KSPPREONLY if you run with -ksp_type richardson or -ksp_type gmres then -ksp_monitor_true_residual will print the residual as you want.<br>
<br>
Barry<br>
<br>
><br>
> Thanks,<br>
><br>
> Yan<br>
<br>
</blockquote></div><br>