[petsc-users] How to set up an interface-type problem

[Matthew Knepley]

On Thu, Oct 20, 2016 at 1:22 AM, Safin, Artur <aks084000 at utdallas.edu>
wrote:

> Hi all,
>
> I would like to get your advice on how to set up an interface problem that
> I get from domain decomposition. The particular issue that I am dealing
> with is how to 'stack' two vectors on top of each other.
>
> I would like to set up a problem of type
>
> [ A   B ] [ x ]  = [ b ]
> [ C   D ] [ y ]    [ c ]
>
> where x and y live on a subset of the global domain (the interface to be
> exact, obtained with VecGetSubVector). I want to solve this system with
> an iterative method. I already have the x and y vectors, but in order to
> set up the system I believe I will need a vector that looks like v = [x;
> y]. Is there a way to set up a vector like this? It would also be
> beneficial if I could extract either the x or y component of the solution
> vector back into the corresponding subvector.
>
> Also, just in general, I am curious as to how one would approach setting
> up these kinds of problems.
>

You use


http://www.mcs.anl.gov/petsc/petsc-current/docs/manualpages/Mat/MatGetLocalSubMatrix.html

http://www.mcs.anl.gov/petsc/petsc-current/docs/manualpages/Vec/VecGetSubVector.html

to put values directly into the subvectors and submatrices. This interacts
well with MatNest, so it
can be optimized after you get it working.

   Matt


> Thanks,
>
> Artur
>
>


-- 
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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