>>On 2012-11-24 23:28:51?"Jed Brown" <jedbrown at mcs.anl.gov> ???
>>On Sat, Nov 24, 2012 at 1:14 PM, w_ang_temp <w_ang_temp at 163.com> wrote:
>>Hello,
>> As is know, GMRES(m) is a very efficient solver when dealing with
>> symmetric indefinite
>>system.
>If you use an SPD preconditioner, then MINRES is equivalent to full GMRES
>(without restarts), but uses a short recurrence.
>>And the restarted parameter m is critical. When the system is small, I can do
>>several tests to find a suitable m. But when the system is very large, it is
>>very difficult
>>to do that. I read lots of papers about GMRES(m) and find that almost none
>>told the way to
>>get a suitable m. Someone told me that I can just choose the matrix dimension
>>as the m, but
>>I find that it is not right.
>Using that restart makes GMRES just an inefficient way to compute a dense QR
>factorization, impractical unless the method converges much sooner.
>In practice, you choose the restart length to balance the cost of
>orthogonalizing and storage with the convergence rate.
So, is there no effective way to determine a suitable m? Only by doing lots
of tests to find
an appropriate value in practical application? Or something need to be
noticeable of using GMRES
with an effective way?
Jim
>> So, generally, when using GMRES(m) as the sovler, how to use a suitable
>> restarted m?
>> Thanks.
>> Jim
-------------- next part --------------
An HTML attachment was scrubbed...
URL:
<http://lists.mcs.anl.gov/pipermail/petsc-users/attachments/20121125/2142ef16/attachment.html>
