KSP/PC choice

[gaatenek at irisa.fr]

Dear Tims,
MUMPS is direct solver so you do not need Krylov subspace which are
generally iterative solver.
May be you are using MUMPS as solver in you problem not as preconditionner.
Regards


> Dear Matt
>
> On Wed, 25 Jul 2007, Matthew Knepley wrote:
>
>>> -ksp_type preonly
>>> -pc_type lu
>>> -mat_type aijmumps
>>> -ksp_monitor
>>>
>> It appears that you never call MatSetFromOptions() on the matrix you
>> create, which would prevent the option from changing the type.
>
> Thank you very much for your help.  Now, the MUMPS solver is working
> for me, and it really seems to solve the problem that I was working on
> for nearly a year now!
>
> However, I have one more question: I usually call
> KSPGetIterationNumber() after the solve, and if it tells me that 0 KSP
> iterations have been used, I assume that the initial guess was already
> accurate enough.  In this case, I don't have to solve the system in
> the next time steps anymore until some change of the setting takes
> place (which happens from time to time in my application).  This saves
> a lot of computational time.  However, with the MUMPS solver,
> KSPGetIterationNumber() never supplies 0.  Is there any possibility to
> find out whether the initial guess was accurate enough?
>
> (It might be noteworthy that I use "-ksptype richardson" instead of
> "-ksptype preonly" since in the latter case I get an error message due
> to my non-zero initial guess.)
>
> Also, I would like to know whether there is any possibility to monitor
> the convergence of the MUMPS solver (analogously to -kspmonitor).
>
> Best Regards,
>
> Tim
>
> --
> Dr. Tim Kroeger                            Phone +49-421-218-7710
> tim at mevis.de, tim at cevis.uni-bremen.de      Fax   +49-421-218-4236
>
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