[petsc-users] MatSetValues on same column multiple times

[Matthew Knepley]

On Tue, Sep 25, 2012 at 6:01 PM, John Mousel <john.mousel at gmail.com> wrote:

> Thanks Matt. Are you allowed to insert the same column multiple times in
> one call to MatSetValues though?
>

Should not be a problem. If it is, its a bug.

  Matt


> On Tue, Sep 25, 2012 at 4:58 PM, Matthew Knepley <knepley at gmail.com>wrote:
>
>> On Tue, Sep 25, 2012 at 5:56 PM, John Mousel <john.mousel at gmail.com>wrote:
>>
>>> To be more clear, I do the following:
>>>
>>> <preallocate>
>>> <insert 0's where I want columns>
>>> <flush>
>>> <insert real entries>
>>> <flush>
>>> <clean up special rows by adding corrections to coefficients>
>>>
>>> What I want to clarify is if I touch the same column more than once, say
>>> I'm looping over neighbors in an octree mesh, and it's just easier to
>>> insert them multiple times as I find them for fluxes in different
>>> directions instead of finding one exact coefficient for each neighbor, how
>>> much preallocation would I need to specify? The number of times it gets
>>> touched, or just one?
>>>
>>
>> Just once. This is exactly how we operate with DMCreateMatrix(). You can
>> test it in any of the examples, like SNES ex5.
>>
>>     Matt
>>
>>
>>> John
>>>
>>>
>>> On Tue, Sep 25, 2012 at 4:50 PM, Matthew Knepley <knepley at gmail.com>wrote:
>>>
>>>> On Tue, Sep 25, 2012 at 5:44 PM, John Mousel <john.mousel at gmail.com>wrote:
>>>>
>>>>>
>>>>> If I'm adding to a particular column in multiple passes, do I need to
>>>>> preallocate enough memory for each pass, or just 1 for each column in the
>>>>> row?
>>>>> Right now I'm drastically over-allocating, and I'm trying to reduce
>>>>> this. If I give the true number of columns in the row, I keep getting new
>>>>> entry errors.
>>>>>
>>>>> New nonzero at (8045,60) caused a malloc!
>>>>>
>>>>
>>>> You have to be more specific. It sounds like what you are doing is
>>>>
>>>> <preallocate>
>>>> <put in some nonzeros>
>>>> <assemble>
>>>> <try to put in more nonzeros>
>>>>
>>>> This will not work since assembly squeezes out extra space. Why are you
>>>> assembling in between?
>>>> If you need to clear buffers, you can just to MAT_ASSEMBLY_FLUSH.
>>>>
>>>>    Matt
>>>>
>>>>
>>>>> I have it spit into phases where I set zeros in the non-zero pattern,
>>>>> then I come back and fill in entries in a bulk pass, and then do a second
>>>>> pass to clean up entries in special rows.
>>>>> Could someone clarify how this works.
>>>>>
>>>>> John
>>>>>
>>>>
>>>>
>>>>
>>>> --
>>>> 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
>>>>
>>>
>>>
>>
>>
>> --
>> 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
>>
>
>


-- 
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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