[petsc-users] Symmetric MPIAIJ matrix

[Matthew Knepley]

On Tue, Jul 7, 2015 at 3:36 PM, Bikash Kanungo <bikash at umich.edu> wrote:

> Hi Matthew,
>
> The entries to the last few rows of my matrix has non-local contributions
> from a large number of processors. Since the matrix is symmetric, I need
> not set the non-local entries in the last few rows as they are equal to
> their transpose entries, which on the other hand are stored as local
> entries in their respective processors.
>

This is really a sparse matrix with a low rank update. It is much easier to
handle it this way. There are explicit formulae for the inverse
in terms of the inverse of the two parts (Sherman-Morrison-Woodbury), and
other operations can be similarly simplified. We might not
have all the support now, but pressing forward on this front is likely to
be much more fruitful.

  Thanks,

    Matt


> Thanks,
> Bikash
>
> On Tue, Jul 7, 2015 at 4:25 PM, Matthew Knepley <knepley at gmail.com> wrote:
>
>> On Tue, Jul 7, 2015 at 3:22 PM, Bikash Kanungo <bikash at umich.edu> wrote:
>>
>>> Hi,
>>>
>>> Is there a way to ignore the lower (or upper) triangular entries in an
>>> MATMPIAIJ matrix when I know my matrix is symmetric? I can see a
>>> MAT_SYMMETRIC option in MatSetOption, but I don't think it ignores any
>>> lower (or upper) triangular entry.
>>>
>>
>> Why do you want this?
>>
>>
>>> I cannot use MATMPISBAIJ due to MatMatMult incompatibility with
>>> MATMPIAIJ.
>>>
>>
>> This is the only way. MatMatMult() is quite complex and there is no real
>> advantage to ignoring
>> the entries, so we have not implemented it here.
>>
>>   Matt
>>
>>
>>> Thanks,
>>> Bikash
>>>
>>> --
>>> 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
>>
>
>
>
> --
> 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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