GMRES and PC_RIGHT

[Barry Smith]

On Jun 8, 2009, at 4:32 PM, Lisandro Dalcin wrote:

> On Mon, Jun 8, 2009 at 5:52 PM, Barry Smith<bsmith at mcs.anl.gov> wrote:
>>
>> 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?
>>
>
> I've not tested it, but it seems that KSPInitialResidual (called
> inside KSPSolve_GMRES) handles this well. Moreover, the GMRES restart
> itself depends on proper handling of nonzero initial guesses :-)
>
>>
>>> 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.
>>
>
> I'll do a bit more of testing, mainly regarding nonzero initial
> guesses and diagonal scaling. If the outcome of this is that all is
> working ... Do you agree about considering this a regression (from
> 2.3.3) and pushing a fix in release-3.0.0 ?

    Fine with me.

     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
>>> ---------------
>>> Centro Internacional de Métodos Computacionales en Ingeniería  
>>> (CIMEC)
>>> Instituto de Desarrollo Tecnológico para la Industria Química  
>>> (INTEC)
>>> Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET)
>>> PTLC - Güemes 3450, (3000) Santa Fe, Argentina
>>> Tel/Fax: +54-(0)342-451.1594
>>
>>
>
>
>
> -- 
> Lisandro Dalcín
> ---------------
> Centro Internacional de Métodos Computacionales en Ingeniería (CIMEC)
> Instituto de Desarrollo Tecnológico para la Industria Química (INTEC)
> Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET)
> PTLC - Güemes 3450, (3000) Santa Fe, Argentina
> Tel/Fax: +54-(0)342-451.1594