[petsc-users] MatMatMult involving MPIAIJ and MATNEST

[Matthew Knepley]

On Mon, May 11, 2015 at 8:47 AM, Bikash Kanungo <bikash at umich.edu> wrote:

> Hi Patrick,
>
> Thanks for the clarification. I want it to be an efficient operation. The
> idea is to convert a generalized eigenvalue problem (H*x = lamda*M*x) to a
> standard one (M^{-1}*H*x = lambda*x). The M^{-1} is of type MATNEST whereas
> H is MPIAIJ. In my problem M^{-1} is computed once whereas H changes every
> iteration. So performing low-level matrix multiplication or creating H as
> MATNEST and assembling it from its sub-matrices at every iteration sounds
> inefficient.
>

You can solve these types of things with SLEPc without explicit MatMat.

   Matt


> Regards,
> Bikash
>
> On Mon, May 11, 2015 at 9:21 AM, Patrick Sanan <patrick.sanan at gmail.com>
> wrote:
>
>> MatMatMult with MATNEST does not seem to be supported, based only on the
>> fact that there are no functions of the form MatMatMult_*_MatNest defined
>> with the MATNEST implementation :
>> http://www.mcs.anl.gov/petsc/petsc-current/src/mat/impls/nest/matnest.c.html
>>
>> Does this operation need to be efficient? (That is, are you forming this
>> matrix for debugging or experimental purposes, or with the intention of
>> using it within an efficient, scalable piece of code?). If not, it should
>> be possible to use lower-level matrix operations as defined by the API to
>> extract the appropriately-sized submatrices from A and (assuming that
>> MatMatMult is defined between MATMPIAIJ and the submatrices of your
>> Matnest), perform the matrix multiplications and additions "by hand" .
>>
>> On Mon, May 11, 2015 at 2:44 PM, Bikash Kanungo <bikash at umich.edu> wrote:
>>
>>> Hi,
>>>
>>> I have two matrices: A of type MPIAIJ and B of type MATNEST. Is there
>>> any way to perform A*B after B has been assembled from its sub-matrices?
>>>
>>> Thanks,
>>> Bikash
>>>
>>> --
>>> Bikash S. Kanungo
>>> PhD Student
>>> Computational Materials Physics Group
>>> Mechanical Engineering
>>> University of Michigan
>>>
>>>
>>
>
>
> --
> Bikash S. Kanungo
> PhD Student
> Computational Materials Physics Group
> Mechanical Engineering
> University of Michigan
>
>


-- 
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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