[petsc-users] MatSetValues and Zero enteries

[Matthew Knepley]

On Mon, Jun 20, 2011 at 9:31 PM, Mohammad Mirzadeh <mirzadeh at gmail.com>wrote:

> Thanks John -- taht's helpful. Do you also know how I can change the
> tolerance for dropping elements?
>

Right now, this only discards entires which are exactly floating point 0.0.

   Matt


> Mohammad
>
> On Mon, Jun 20, 2011 at 1:12 PM, John Mousel <john.mousel at gmail.com>wrote:
>
>> See the matrix options available in the man pages. I think the function
>> below is what you are looking for.
>>
>>
>> http://www.mcs.anl.gov/petsc/petsc-as/snapshots/petsc-current/docs/manualpages/Mat/MatSetOption.html
>>
>>
>> MatSetOption <http://www.mcs.anl.gov/petsc/petsc-as/snapshots/petsc-current/docs/manualpages/Mat/MatSetOption.html#MatSetOption>(A,MAT_IGNORE_ZERO_ENTRIES,PETSC_TRUE <http://www.mcs.anl.gov/petsc/petsc-as/snapshots/petsc-current/docs/manualpages/Sys/PETSC_TRUE.html#PETSC_TRUE>);
>>
>>
>>
>>
>> Best Regards,
>> John
>>
>>
>>
>>
>> On Mon, Jun 20, 2011 at 2:42 PM, Mohammad Mirzadeh <mirzadeh at gmail.com>wrote:
>>
>>> Hi folks,
>>>
>>> I've noticed that MatSetValues explicitly inserts zeros in the matrix if
>>> an element is really zero. Is there a way to drop elements (or not save them
>>> in the first place) that are below a certain tolerance? I realize one way of
>>> doing it is in the application code and when using MatSetValues but I'm just
>>> wondering if PETSc has a function for it?
>>>
>>> Thanks,
>>> Mohammad
>>>
>>
>>
>


-- 
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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