[petsc-users] MatMatMult involving MPIAIJ and MATNEST

[Bikash Kanungo]

Hi Patrick,

I have M^{-1} computed explicitly and stored as MATNEST. Providing
MATCOMPOSITE of M^{-1}H to SLEPc standard eigenvalue solvers seems an
option. Does it has any additional cost of explicitly building
On May 11, 2015 1:30 PM, "Patrick Sanan" <patrick.sanan at gmail.com> wrote:

> Are you storing M^{-1} explicitly? In that case you could use MATCOMPOSITE
> to define M^{-1}H and feed that to SLEPc's standard solver. If you only
> have M explicitly, you could use MATSHELL to define your own operator which
> applies M^{-1}H and use that with SLEPc's standard solver (though of course
> SLEPc would be free to implement its generalized eigensolvers this way
> and/or in better ways for certain problems - I am not enough of an expert
> on that library to say more).
>
> On Mon, May 11, 2015 at 7:12 PM, Bikash Kanungo <bikash at umich.edu> wrote:
>
>> Hi Matthew,
>>
>> Yes SLEPc does allow me to solve a generalized eigenvalue problem. But
>> the generalized solvers are not as robust as the standard eigenvalue
>> solvers. That's the reason I want to use explicit MatMatMult so that I can
>> use standard eigenvalue solvers.
>>
>> Thanks,
>> Bikash
>> On May 11, 2015 1:00 PM, "Matthew Knepley" <knepley at gmail.com> wrote:
>>
>>> 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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