[petsc-users] Symmetric MPIAIJ matrix

[Bikash Kanungo]

Hi Matthew,

I couldn't follow your reply. It seems a bit unrelated to my query.

Thanks,
Bikash

On Tue, Jul 7, 2015 at 4:42 PM, Matthew Knepley <knepley at gmail.com> wrote:

> 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
>



-- 
Bikash S. Kanungo
PhD Student
Computational Materials Physics Group
Mechanical Engineering
University of Michigan
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