[petsc-users] Question about KSP

[Matthew Knepley]

On Thu, May 19, 2016 at 7:43 AM, Elias Karabelas <
elias.karabelas at medunigraz.at> wrote:

> 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.
>

We do understand PCs for saddle point problems, but I do not know of
anything for A+rank 1, except updated factorizations.

   Matt


> 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>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>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>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 <%2B43%20316%20380%207759>
>>>> Email: <elias.karabelas at medunigraz.at>elias.karabelas at medunigraz.at
>>>> Web  : <http://forschung.medunigraz.at/fodok/staff?name=EliasKarabelas>
>>>> 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
>>>
>>>
>>
>>
>> --
>> 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
>>
>>
>
>
> --
> 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
>
>


-- 
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
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