[petsc-users] Construct Matrix based on row and column values
Elias Karabelas
karabelaselias at gmail.com
Mon Mar 23 09:17:28 CDT 2020
Ok I'll try to decipher that. Thought that I would maybe find something
in the GAMG routines but I'll be happy to scroll through the ASM stuff :D
On 23/03/2020 13:56, Matthew Knepley wrote:
> On Mon, Mar 23, 2020 at 8:41 AM Elias Karabelas
> <karabelaselias at gmail.com <mailto:karabelaselias at gmail.com>> wrote:
>
> Thanks I'll have a look at it. So I understand correctly, that
> purely algebraic is not the way to go through PETSc here?
>
> You can make it work. You would have the same difficulty in any linear
> algebra package, namely that you need
> an overlapped decomposition of the matrix, which no package does by
> default. PETSc does it for ASM, so you could
> use those routines to get what you want.
>
> Thanks,
>
> Matt
>
> Cheers
>
> Elias
>
> On 23/03/2020 13:39, Matthew Knepley wrote:
>> On Mon, Mar 23, 2020 at 8:38 AM Elias Karabelas
>> <karabelaselias at gmail.com <mailto:karabelaselias at gmail.com>> wrote:
>>
>>
>> On 23/03/2020 13:36, Matthew Knepley wrote:
>>> On Mon, Mar 23, 2020 at 8:31 AM Elias Karabelas
>>> <karabelaselias at gmail.com <mailto:karabelaselias at gmail.com>>
>>> wrote:
>>>
>>> Dear Matt,
>>>
>>> I've just found this answer from 2014
>>>
>>> https://lists.mcs.anl.gov/pipermail/petsc-users/2014-August/022450.html
>>>
>>> wondering if this would theoretically work.
>>>
>>> In serial certainly, I just don't see how it works in
>>> parallel since you might not own the row you need from the
>>> transpose.
>>>
>>> And the thing with this FCT-Schemes is, that they're
>>> build on purely algebraic considerations (like AMG) so I
>>> don't want to break it back down to mesh information if
>>> possible at all.
>>>
>>> The FEM-FCT I am familiar with from Lohner was phrased on a
>>> mesh.
>>
>> Can you give me a reference to that? I based my things on
>> this work
>> https://www.sciencedirect.com/science/article/pii/S0045782508003150#!
>>
>> Volker is of course great. I believe I was thinking of
>> https://onlinelibrary.wiley.com/doi/abs/10.1002/fld.1650071007
>>
>> Thanks,
>>
>> Matt
>>
>> Best regards
>>
>> Elias
>>
>>
>>>
>>> Thanks,
>>>
>>> Matt
>>>
>>> Best regards
>>>
>>> Elias
>>>
>>> On 23/03/2020 13:02, Matthew Knepley wrote:
>>>> On Mon, Mar 23, 2020 at 7:46 AM Elias Karabelas
>>>> <karabelaselias at gmail.com
>>>> <mailto:karabelaselias at gmail.com>> wrote:
>>>>
>>>> Dear Users,
>>>>
>>>> I want to implement a FCT (flux corrected
>>>> transport) scheme with PETSc.
>>>> To this end I have amongst other things create a
>>>> Matrix whose entries
>>>> are given by
>>>>
>>>> L_ij = -max(0, A_ij, A_ji) for i neq j
>>>>
>>>> L_ii = Sum_{j=0,..n, j neq i} L_ij
>>>>
>>>> where Mat A is an (non-symmetric) Input Matrix
>>>> created beforehand.
>>>>
>>>> I was wondering how to do this. My first search
>>>> brought me to
>>>> https://www.mcs.anl.gov/petsc/petsc-current/src/mat/examples/tutorials/ex16.c.html
>>>>
>>>>
>>>>
>>>> but this just goes over the rows of one matrix to
>>>> set new values and now
>>>> I would need to run over the rows and columns of
>>>> the matrix. My Idea was
>>>> to just create a transpose of A and do the same but
>>>> then the row-layout
>>>> will be different and I can't use the same for loop
>>>> for A and AT and
>>>> thus also won't be able to calculate the max's above.
>>>>
>>>> Any help would be appreciated
>>>>
>>>>
>>>> I think it would likely be much easier to write your
>>>> algorithm directly on the mesh, rather than using
>>>> matrices, since the locality information is explicit
>>>> with the mesh, but has to be reconstructed with the matrix.
>>>>
>>>> The problem here is that in parallel there would be no
>>>> easy way to get the halo you need using a matrix. You
>>>> really want the ghosted space for assembly, and that is
>>>> provided by the DM objects. Does this make sense?
>>>> Unless anybody in PETSc has a better idea.
>>>>
>>>> Thanks,
>>>>
>>>> Matt
>>>>
>>>> Best regards
>>>>
>>>> Elias
>>>>
>>>>
>>>>
>>>> --
>>>> 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
>>>>
>>>> https://www.cse.buffalo.edu/~knepley/
>>>> <http://www.cse.buffalo.edu/~knepley/>
>>>
>>>
>>>
>>> --
>>> 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
>>>
>>> https://www.cse.buffalo.edu/~knepley/
>>> <http://www.cse.buffalo.edu/~knepley/>
>>
>>
>>
>> --
>> 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
>>
>> https://www.cse.buffalo.edu/~knepley/
>> <http://www.cse.buffalo.edu/~knepley/>
>
>
>
> --
> 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
>
> https://www.cse.buffalo.edu/~knepley/
> <http://www.cse.buffalo.edu/~knepley/>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.mcs.anl.gov/pipermail/petsc-users/attachments/20200323/13729fcd/attachment-0001.html>
More information about the petsc-users
mailing list