[petsc-users] MatSetSizes with blocked matrix

[Steena Monteiro]

Thank you, Dave.

Matt: I understand the inconsistency but MatMult with non divisible block
sizes (here, 2) does not throw any errors and fail, when MatSetSize is
commented out. Implying that 1139905 global size does work with block size
2.

On 15 March 2016 at 00:12, Dave May <dave.mayhem23 at gmail.com> wrote:

>
> On 15 March 2016 at 04:46, Matthew Knepley <knepley at gmail.com> wrote:
>
>> On Mon, Mar 14, 2016 at 10:05 PM, Steena Monteiro <steena.hpc at gmail.com>
>> wrote:
>>
>>> Hello,
>>>
>>> I am having difficulty getting MatSetSize to work prior to using MatMult.
>>>
>>> For matrix A with rows=cols=1,139,905 and block size = 2,
>>>
>>
>> It is inconsistent to have a row/col size that is not divisible by the
>> block size.
>>
>
>
> To be honest, I don't think the error message being thrown clearly
> indicates what the actual problem is (hence the email from Steena). What
> about
>
> "Cannot change/reset row sizes to 400000 local 1139906 global after
> previously setting them to 400000 local 1139905 global. Local and global
> sizes must be divisible by the block size"
>
>
>>
>>   Matt
>>
>>
>>> rank 0 gets 400000 rows and rank 1 739905 rows,  like so:
>>>
>>> /*Matrix setup*/
>>>
>>> ierr=PetscViewerBinaryOpen(PETSC_COMM_WORLD,file,FILE_MODE_READ,&fd);
>>> ierr = MatCreate(PETSC_COMM_WORLD,&A);
>>> ierr = MatSetFromOptions(A);
>>> ierr = MatSetType(A,MATBAIJ);
>>> ierr = MatSetBlockSize(A,2);
>>>
>>> /*Unequal row assignment*/
>>>
>>>  if (!rank) {
>>>     ierr = MatSetSizes(A, 400000, PETSC_DECIDE,
>>> 1139905,1139905);CHKERRQ(ierr);
>>>    }
>>> else {
>>>     ierr = MatSetSizes(A, 739905, PETSC_DECIDE,
>>> 1139905,1139905);CHKERRQ(ierr);
>>> }
>>>
>>> MatMult (A,x,y);
>>>
>>> /************************************/
>>>
>>> Error message:
>>>
>>> 1]PETSC ERROR: [0]PETSC ERROR: No support for this operation for this
>>> object type
>>> Cannot change/reset row sizes to 400000 local 1139906 global after
>>> previously setting them to 400000 local 1139905 global
>>>
>>> [1]PETSC ERROR: [0]PETSC ERROR: Cannot change/reset row sizes to 739905
>>> local 1139906 global after previously setting them to 739905 local 1139905
>>> global
>>>
>>> -Without messing with row assignment,  MatMult works fine on this matrix
>>> for block size = 2, presumably because an extra padded row is automatically
>>> added to facilitate blocking.
>>>
>>> -The above code snippet works well for block size = 1.
>>>
>>> Is it possible to do unequal row distribution *while using blocking*?
>>>
>>> Thank you for any advice.
>>>
>>> -Steena
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>
>>
>> --
>> 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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