[petsc-users] converting parallel matrix MATMPIJ to MATAIJ
Lukasz Kaczmarczyk
Lukasz.Kaczmarczyk at glasgow.ac.uk
Fri Sep 6 17:44:48 CDT 2013
Thanks, for very fast help,
Last qestion, how I should interpret,
PetscInt mlocal_red, i.e. number of local rows of the redundant matrix,
what if mlocal_red is smaller than total number or rows in mat.
Lukasz
On 6 Sep 2013, at 23:37, Barry Smith <bsmith at mcs.anl.gov> wrote:
>
>
> MPI_Comm_size(PETSC_COMM_WORLD,&Np);
>
> Use Np and MPI_COMM_NULL. Note that you should be using PETSc from https://bitbucket.org/petsc/petsc
>
> Barry
>
> Yes, the phrasing is a little confusing.
>
> On Sep 6, 2013, at 5:32 PM, Lukasz Kaczmarczyk <Lukasz.Kaczmarczyk at glasgow.ac.uk> wrote:
>
>> On 6 Sep 2013, at 23:00, Barry Smith <bsmith at mcs.anl.gov> wrote:
>>
>>>
>>> I would use MatGetRedundantMatrix()
>>>
>>>
>>> On Sep 6, 2013, at 4:52 PM, Matthew Knepley <knepley at gmail.com> wrote:
>>>
>>>> On Fri, Sep 6, 2013 at 4:25 PM, Lukasz Kaczmarczyk <Lukasz.Kaczmarczyk at glasgow.ac.uk> wrote:
>>>> Hello,
>>>>
>>>> I solve system of eq. generated by finite element method.
>>>>
>>>> I apply some projection matrix to stiffness matrix K,
>>>> P=I-CT[(CTC)^-1]C
>>>> where C is some not square matrix.
>>>>
>>>> Resulting stiffness matrix K' has form
>>>> K' = PT K P,
>>>> with that at hand I solve problem K' *x = f'
>>>>
>>>> I manage to build shell matrix where I use sub ksp solver to get solution for (CTC)*b = C*x, where [ b = (CTC^-1*C*x)] . Using penalised matrix for preconditioner, where K_prec = alpha*CCT + K, where alpha is penalty I can get solution in efficient way.
>>>>
>>>> Now I like to avoid penalty parameter, in order to do that I will need to apply penalty matrix for each individual finite element matrix before it is assembled into K. No problem with that, using scattering it can be done.
>>>>
>>>> Problem is with solution (CTC)*b = C*x, C and CTC matrices are parallel, since I have parallelised assembly functions, problem (CTC)*b = C*x need to be solved on each processor independently without communication. It is not problem, but to do that I need to transform C and CTC matrix form MATMPIAIJ to MATAIJ.
>>>>
>>>> I think this might be what you want:
>>>>
>>>> http://www.mcs.anl.gov/petsc/petsc-current/docs/manualpages/Mat/MatGetSubMatrices.html
>>>>
>>>> Thanks,
>>>>
>>>> Matt
>>>>
>>>> I know that MatConvert will not do it. I wonder it is any other way that form very beginning to assemble matrix C as a serial matrix.
>>>>
>>>> Regards,
>>>> Lukasz
>>>>
>>>>
>>>>
>>>>
>>>>
>>>>
>>>>
>>>> --
>>>> 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
>>>
>>
>> Thanks Matt and Barry,
>>
>> Sorry for taking your time, I should find that by myself.
>> How to use MatGetSubMatrices is clear.
>>
>> I have feeling that MatGetRedundantMatrix could be more efficient. However, apologise my ignorance, I have problem with MatGetRedundantMatrix,
>>
>> *) is this should be equal to number of process in the communicator group, in my case 1 since I like to use PETSC_COMM_SELF?
>> nsubcomm - the number of subcommunicators (= number of redundant parallel or sequential matrices)
>> subcomm - MPI communicator split from the communicator where mat resides in
>>
>> *) it could be equal to total number of rows in MPIAIJ? What if this number is smaller, the first mlocal_red are stored in redundant matrix?
>> mlocal_red - number of local rows of the redundant matrix
>>
>>
>> Regards,
>> Lukasz
>>
>>
>
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