KSP/PC choice

[Matthew Knepley]

1) Until you run out of memory, I would use sparse direct like MUMPS

2) After that, as long as you have the memory I would increase the
GMRES vectors, say to 50 or 100.

3) After that I would try LGMRES which generally converges better on these
    problems.

   Matt

On 7/23/07, Tim Kröger <tim at cevis.uni-bremen.de> wrote:
> Dear Lissandro,
>
> On Mon, 23 Jul 2007, Lisandro Dalcin wrote:
>
> > On 7/23/07, Tim Kröger <tim at cevis.uni-bremen.de> wrote:
> >>
> >> the more KSP and PC methods are available, the more difficult it is to
> >> choose a suitable one.
> >>
> >> I want to compute Navier-Stokes (using Finite Elements) for
> >> medium-sized Reynolds numbers (still laminar, though).  I am currently
> >> using
> >
> > Are you solving incompresible flow?
>
> Yes.
>
> > Tansient or steady state?
>
> Transient.
>
> > Are you using a monolithic formulation; or a fractional-step like
> > formulation?
>
> Monolithic.  (I am not quite sure about this word but I assume it
> means that I don't try to decouple the two equations.)
>
> > What kind of stabilization for advection and pressure are you using?
>
> Streamline diffusion (for advection).  I am not aware of the
> requirement to stabilize the pressure as well.
>
> > I ask this because in my experience incompressible flows with
> > monolithic formulations are usually hard to solve, and a good choice
> > of stabilization method not only leads to better final solution, but
> > also lead to linear systems with better conditioning.
>
> Would you recommend to use a fractional step method?  Would you
> recommend a different stabilization method?  If you have any
> suggestion, please let me know.
>
> Best Regards,
>
> Tim
>
> --
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>
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