[petsc-users] Functions for judging the properties of the matrix
Satish Balay
balay at mcs.anl.gov
Tue Aug 7 10:05:19 CDT 2012
For eg: -ksp_gmres_restart 1000 -ksp_max_it 1000 [default] avoids restarts
But if your code doesn't converge before 1000 iterations - perhaps use:
-ksp_gmres_restart 2000 -ksp_max_it 2000
Satish
On Tue, 7 Aug 2012, w_ang_temp wrote:
> Hello,
> I am sorry that I cannot understand "Make sure to avoid restarts". In the FAQ, it says that using the restarted
> GMRES method to get approximations to the condition number. So why saying "avoid restarts" in the next following?
> Besides, there are two questions about GMRES:
> (1) Is the "iterations count" of GMRES with restarted parameters which is outputted by PETSc meaningless?
> (2) Is there only restarted GMRES in PETSc?
> Thanks.
> Jim
>
>
>
>
> >>在 2012-08-07 21:59:05，"Matthew Knepley" <knepley at gmail.com> 写道：
> >>On Tue, Aug 7, 2012 at 8:56 AM, w_ang_temp <w_ang_temp at 163.com> wrote:
>
>
> >>Hello, Jed
> >> I am a little puzzled about the "How can I determine the condition number of a matrix?" in the
> >>FAQ. The details are as follows:
>
> >> "...For larger matrices, you can run with -pc_type none -ksp_type gmres -ksp_monitor_singular_value
> >>-ksp_gmres_restart 1000 to get approximations to the condition number of the operator. This will
> >>generally be accurate for the largest singular values, but may overestimate the smallest singular
> >>value unless the method has converged. Make sure to avoid restarts...".
>
> >> Since the command "-pc_type none -ksp_type gmres -ksp_monitor_singular_value
> >>-ksp_gmres_restart 1000" using restart parameter, so, what does "Make sure to avoid restarts" mean?
>
>
> >Do not believe the answer after the restart.
>
> >>Besides, is the parameter "1000" a reference value which will be changed in specific project in order
> >>to be converged? Or must use 1000 to get the condition number?
>
>
> >The former.
>
>
> > Matt
>
> >> Thanks.
> >> Jim
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