[petsc-users] MatSetValues and Zero enteries

[Mohammad Mirzadeh]

Matt,

I see. Please forgive my ignorance, but I don't quite understand why you
should not be able to set a tolerance for it. Could you please point me to
the source file that applies the MAT_IGNORE_ZERO_ENTRIES option to the
matrix? I may be able to manually modify it.

Thanks,
Mohammad

On Mon, Jun 20, 2011 at 2:34 PM, Matthew Knepley <knepley at gmail.com> wrote:

> 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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