[petsc-users] [DMMG] Stokes Solver

[domenico.borzacchiello at univ-st-etienne.fr]

Ok, I'll keep that in mind.
thank you very much for the explanations.

Domenico.

> On Mon, Apr 11, 2011 at 13:32,
> <domenico.borzacchiello at univ-st-etienne.fr>wrote:
>
>> Still it's unclear to me why this happens and whether or not defining
>> the
>> Jacobian instead of computing it by FD may possibly fix it. I'd like to
>> stick with FD approximation of Jacobian because I'll add complex
>> rheology
>> models for which computing the Jacobian analitically won't be an easy
>> task.
>>
>
> To use FD, you have to make sure that your equations are well scaled. You
> should be able to volume-scale the residual (most PETSc examples do this)
> and choose units such that the system is well-scaled independent of grid
> resolution. You should do this regardless of whether you use FD, but with
> FD, you have half the number of digits to work with before running into
> rounding error problems.
>