[petsc-users] different convergence behaviour

[Hoang Giang Bui]

I used

-ksp_monitor_true_residual
-ksp_monitor_true_solution
-ksp_converged_reason

with MUMPS but it does not compute the true residual. Should I compute that
myself?

Below is a sample for a full log of MUMPS
https://www.dropbox.com/s/fy5uknooxw77r19/log13Jun16_mumps?dl=0


Giang

On Fri, Jul 15, 2016 at 2:52 AM, Mark Adams <mfadams at lbl.gov> wrote:

>
>
> On Thu, Jul 14, 2016 at 7:29 PM, Matthew Knepley <knepley at gmail.com>
> wrote:
>
>> On Thu, Jul 14, 2016 at 6:27 PM, Mark Adams <mfadams at lbl.gov> wrote:
>>
>>>
>>>>
>>>> Notice that there are 7 orders of magnitude between the apparent
>>>> residual (using the preconditioner), and the actual residual, Ax - b.
>>>> You are using Hypre, and this generally means the Hypre coarse grid
>>>> operator is crap. Please
>>>>
>>>>
>>> Huh?, this data looks fine, both the true and preconditioned residual
>>> stay separated by about 9 orders of magnitude. This just tells you that the
>>> norm of A (or is it A^-1) is 10^9.  Am I misunderstanding this?
>>>
>>
>> This is why Barry and I asked for a comparsion with MUMPS. If you are
>> right, and its just the condition number,
>>
>
> I said norm not condition number. I trust I'm missing something in this
> thread.
>
>
>> the LU
>> will not be any more accurate.
>>
>>    Matt
>>
>> --
>> 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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