memory usage of a SeqAIJ matrix

[Bernardo Rocha]

Thanks a lot! =)

2009/9/15 Matthew Knepley <knepley at gmail.com>

> You can use the output of -ksp_view, which gives the matrix information.
>
>    Matt
>
>
> On Tue, Sep 15, 2009 at 2:01 PM, Bernardo Rocha <bernardosk at gmail.com>wrote:
>
>> Hi everyone,
>>
>> I need to know the number of nonzero element of the matrix in an
>> application using PETSc. How can I do it? What is the best way to do it?
>>
>> As far as I'm concerned with PETSc, running on a single processor, I'm
>> using the command line argument "-info" and then I get this information in
>> some line of the output that looks like this
>>
>> [0] MatAssemblyEnd_SeqAIJ(): Matrix size: 5100 X 5100; storage space:
>> 92706 unneeded,44994 used
>>
>> then I simply get the number of used entries.
>>
>> But when I have a large simulation, where the matrix does not fit into the
>> memory of one processor, I must use several processors. My question is how
>> to get the number of nonzero entries of the "global" matrix? I wrote a
>> simple python script to parse the output and sum the number of entries used
>> on each processor, but I found out that my calculations are wrong, I'm
>> having twice more nonzero elements (I tested against a tiny simulation on a
>> single processor). It seems that on the output I'm parsing I have two kinds
>> of informations about the entries used:
>>
>> [0] MatAssemblyEnd_SeqAIJ(): Matrix size: 5100 X 5100; storage space:
>> 92706 unneeded,44994 used
>>
>> [0] MatAssemblyEnd_SeqAIJ(): Matrix size: 5100 X 5100; storage space: 0
>> unneeded,44994 used
>>
>> That is, one that the "unneeded" field has some value and another that
>> this field is zero. Then I decided to discard the information where the
>> field "unneeded" is zero and finally the results matched perfectly with a
>> single processor case.
>>
>> So, i would like to know (1) why do I have these lines with "0 unneeded"
>> and (2) if there is a more elegant way to measure this.
>>
>> That's all!
>> Best regards,
>> Bernardo M. R.
>>
>
>
>
> --
> 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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