[petsc-users] converting parallel matrix MATMPIJ to MATAIJ

[Barry Smith]

  It is gone.  Use the development version of petsc

On Sep 6, 2013, at 5:44 PM, Lukasz Kaczmarczyk <Lukasz.Kaczmarczyk at glasgow.ac.uk> wrote:

> 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 
>>> 
>>> 
>> 
>