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Re: KSP/PC choice

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@xxxxxxxxxxxxxxxxxxx> wrote: 
Dear Lissandro,

On Mon, 23 Jul 2007, Lisandro Dalcin wrote:

> On 7/23/07, Tim Kröger <tim@xxxxxxxxxxxxxxxxxxx> 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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