[petsc-users] Running the same problem multiple time, but the matrix is not the same

[Khai Pham]

Hi Hong,

I more concern about the difference between A1 and A2 is in the order of
O(1.e-8) as I run the same code twice. Should it be in the order of machine
epsilon?

Khai

On Thu, Dec 8, 2016 at 4:54 PM, Hong <hzhang at mcs.anl.gov> wrote:

> Khai :
>>
>> Thanks for your response. The output is not the solution. They are the
>> component of the matrix in matlab format. I would expect the difference in
>> the order of machine precesion. The difference in solutions in two runs is
>> in the order of 1e-5.
>>
>
> If your matrices A1 and A2 have difference of O(1.e-8), then the computed
> solution may differ by
> Condition_number(A) * machine_epsion. Do you know cond(A)?
>
> Please alway send your request to petsc-maint.
>
> Hong
>
>>
>>
>> On Dec 8, 2016 4:01 PM, "Hong" <hzhang at mcs.anl.gov> wrote:
>>
>> Khai :
>> Your solution components have values ranging from 1.e+9 to 1.e-8, and the
>> values only differ in the order of 1.e-8, which are within computational
>> error tolerance.
>> I would consider all solutions same within the approximation tolerance.
>>
>> Hong
>>
>> Hello,
>>>
>>> I have problem with matrix assembly for linear solver KSP. I run the the
>>> same problem with 4 processors multiple time. Using flag
>>> -mat_view ::ascii_matlab to view the matrix. The matrix outputs are not the
>>> same during each run. Please see the attached file for the comparison
>>> between two runs. I checked all the input for each processor as it calls to
>>> MatSetValues ( indices of the matrix and values ) and it's consistent all
>>> the time. I also checked the allocation information (with flag -info) and
>>> it looks fine. Could you give me an advice how to deal with this issue?
>>> Thanks !
>>>
>>> Best,
>>> Khai
>>>
>>
>>
>>
>
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