GMRES and PC_RIGHT

[Barry Smith]

On Jun 8, 2009, at 3:46 PM, Lisandro Dalcin wrote:

> Well, all you say that GMRES is not coded for right PC's, however,
> after reviewing (in a hurry) the code for GMRES, it seems to handle
> right preconditioner. Moreover, I've just tested solving (with SNES) a
> steady lid-driven cavity flow in 2d with linear quads using SUPG/PSPG,
> default tolerances, default restart, no diag-scaling, starting with
> zero nonlinear guess ...

    Does nonzero initial guess work properly?


> in short, using -ksp_right_pc and just
> changing -ksp_type to gmres/fgmres, and ALL the SNES iterates (up to 3
> nonlinear its) and GMRES|FGMRES iterates (64, 169, 177 linear its) are
> almost the same (except the last four digits using default KSP
> monitor).
>
> Sorry for the insistence, but ...  Am I missing something? Do any of
> you remember exactly what part of GMRES had problems with right
> preconditioning?

    Sadly, no I do not remember the exact issue with right  
preconditioner; I was thinking it was more or less completely broken.

    Barry

>
>
>
> On Mon, Jun 8, 2009 at 4:27 PM, Jed Brown<jed at 59a2.org> wrote:
>> Barry Smith wrote:
>>
>>>    The FGMRES code was written for right preconditioning (but the  
>>> FGMRES
>>> algorithm itself does not support left preconditioning.)
>>
>> LGMRES has both so that's another option.
>>
>> Jed
>>
>>
>
>
>
> -- 
> Lisandro Dalcín
> ---------------
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