[petsc-users] Question about KSP

[Elias Karabelas]

Well I don't bother to much about which PC is use. I just wanted to look 
what's possible. One can of course come up with some kind of augmented 
Lagrange formulation, but then you end up with a saddle point problem.

On 19.05.2016 14:41, Matthew Knepley wrote:
> On Thu, May 19, 2016 at 7:39 AM, Elias Karabelas 
> <elias.karabelas at medunigraz.at <mailto:elias.karabelas at medunigraz.at>> 
> wrote:
>
>     Ok maybe I should go a little bit more into detail. I have some
>     stokes problem in a bifurcating Y-tube. Now I would like to
>     enforce some prescribed flux splits at the outlets. After some
>     literature research i found a Nitsche method to do that. And if
>     you consider the additional billinear forms you end up with some
>     nonlocal coupling terms at the outlets (which are those vectors I
>     talked earlier)
>
>
> Keep the Cc.
>
> I can see that you might have that formulation, but how you would 
> incorporate that into AMG, I have no idea.
>
>    Matt
>
>
>     On 19.05.2016 14:31, Matthew Knepley wrote:
>>     On Thu, May 19, 2016 at 7:29 AM, Elias Karabelas
>>     <elias.karabelas at medunigraz.at
>>     <mailto:elias.karabelas at medunigraz.at>> wrote:
>>
>>         maybe something with PCSHELL?
>>
>>
>>     No, I mean that I do not understand what algorithm you might use
>>     (apart from the implementation).
>>
>>        Matt
>>
>>
>>         On 19.05.2016 14:28, Matthew Knepley wrote:
>>>         On Thu, May 19, 2016 at 2:48 AM, Elias Karabelas
>>>         <elias.karabelas at medunigraz.at
>>>         <mailto:elias.karabelas at medunigraz.at>> wrote:
>>>
>>>             Dear all,
>>>
>>>             I have a question about preconditioned solvers. So, I
>>>             have a Sparsematrix, say A, and now for some reason I
>>>             would like to add some rank-one term u v^T to that matrix.
>>>             As far as I know about Petsc, I can define the action of
>>>             this matrix with MatShell. But is it possible to adapt
>>>             the preconditioner (like a AMG) of my KSP to handle that
>>>             kind of MatShell?
>>>
>>>
>>>         I do not know how you would do that. Its possible other
>>>         people have ideas.
>>>
>>>          Thanks,
>>>
>>>            Matt
>>>
>>>             Kind Regards
>>>             Elias
>>>
>>>             -- 
>>>             Dr Elias Karabelas
>>>
>>>             Medical University of Graz
>>>             Institute of Biophysics
>>>             Harrachgasse 21/IV
>>>             8010 Graz, Austria
>>>
>>>             Phone: +43 316 380 7759 <tel:%2B43%20316%20380%207759>
>>>             Email: elias.karabelas at medunigraz.at
>>>             <mailto:elias.karabelas at medunigraz.at>
>>>             Web  :
>>>             http://forschung.medunigraz.at/fodok/staff?name=EliasKarabelas
>>>
>>>
>>>
>>>
>>>         -- 
>>>         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
>>
>>         -- 
>>         Dr Elias Karabelas
>>
>>         Medical University of Graz
>>         Institute of Biophysics
>>         Harrachgasse 21/IV
>>         8010 Graz, Austria
>>
>>         Phone:+43 316 380 7759 <tel:%2B43%20316%20380%207759>
>>         Email:elias.karabelas at medunigraz.at
>>         <mailto:elias.karabelas at medunigraz.at>
>>         Web  :http://forschung.medunigraz.at/fodok/staff?name=EliasKarabelas  
>>
>>
>>
>>
>>     -- 
>>     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
>
>     -- 
>     Dr Elias Karabelas
>
>     Medical University of Graz
>     Institute of Biophysics
>     Harrachgasse 21/IV
>     8010 Graz, Austria
>
>     Phone:+43 316 380 7759 <tel:%2B43%20316%20380%207759>
>     Email:elias.karabelas at medunigraz.at <mailto:elias.karabelas at medunigraz.at>
>     Web  :http://forschung.medunigraz.at/fodok/staff?name=EliasKarabelas  
>
>
>
>
> -- 
> 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

-- 
Dr Elias Karabelas

Medical University of Graz
Institute of Biophysics
Harrachgasse 21/IV
8010 Graz, Austria

Phone: +43 316 380 7759
Email: elias.karabelas at medunigraz.at
Web  : http://forschung.medunigraz.at/fodok/staff?name=EliasKarabelas

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