[petsc-users] different convergence behaviour

[Mark Adams]

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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