Like using the Krylov preconditioner as a Richardson KSP solver with max_its =
N?
> On Jun 22, 2018, at 1:49 PM, Matthew Knepley <[email protected]> wrote:
>
> On Fri, Jun 22, 2018 at 1:47 PM Boyce Griffith <[email protected]
> <mailto:[email protected]>> wrote:
> Can you set up the preconditioner so that you can just use GMRES?
>
> So I think what Boyce is saying is, can't you fix the number of iterates in
> the inner Krylov solvers so that it becomes a linear
> operator and you can use GMRES?
>
> Thanks,
>
> Matt
>
> On Jun 22, 2018, at 4:33 PM, Nishant Nangia <[email protected]
> <mailto:[email protected]>> wrote:
>
>> Hi,
>>
>> I am solving a saddle point system using a shell preconditioner (which
>> itself uses Krylov solvers, hence the use of FGMRES). I had added the option
>> to re-scale parts of the saddle point system to minimize loss of floating
>> point precision for cases where there are varying orders of magnitude in the
>> system/unknowns.
>>
>> I wanted to show that re-scaling can alleviate large differences between the
>> preconditioned and unpreconditioned residual norms. However, I notice that
>> FGMRES only supports right preconditioning, meaning the preconditioned
>> residual is never formed/used (I think).
>>
>> Is there any way to form the preconditioned norm for FGMRES, or does it just
>> not make sense in the context of right-preconditioned iterative solvers? Is
>> there any way to show that the re-scaling is improving the solver
>> convergence (i.e. showing that it ensures that the true and relative
>> residual are close to each other)?
>>
>> Nishant Nangia
>> Northwestern University
>> Ph.D. Candidate | Engineering Sciences and Applied Mathematics
>> Tech L386
>
>
> --
> What most experimenters take for granted before they begin their experiments
> is infinitely more interesting than any results to which their experiments
> lead.
> -- Norbert Wiener
>
> https://www.cse.buffalo.edu/~knepley/ <http://www.caam.rice.edu/~mk51/>
