[petsc-users] different convergence behaviour

[Matthew Knepley]

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, 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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