[petsc-users] [DMMG] Stokes Solver

[Jed Brown]

On Fri, Apr 8, 2011 at 11:40, <domenico.borzacchiello at univ-st-etienne.fr>wrote:

> I can't get why it takes more than one Newton iteration even if my system
> is linear and the linear solver is direct.
>

The direct solver should also converge in one iteration. Are you only
assembling an approximation of the Jacobian (e.g. using -snes_mf_operator)?
If using MFFD, is the system poorly scaled such that the step size is very
low accuracy (maybe try -mat_mffd_type ds)? Are the equations singular? Is
both the Jacobian and residual evaluation correct?


>
> As for the Vanka smoother would you suggest to implement it with PCSHELL
> or by defining a new PC type?
>

That is up to you. Defining a new PC type makes it more reusable, but
PCShell is a bit quicker to develop. You can start with PCShell and convert
it later.
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