KSP/PC choice

[Barry Smith]

  Ben,

   There is really no way to know what is the best preconditioner/Krylov
approach without trying them on a representative problem.

   Barry


On Wed, 25 Jul 2007, Ben Tay wrote:

> Hi,
> 
> I am also trying to solve the NS eqns in 2d, finite volume mtd, using
> fractional step formulation.
> 
> I am currently using KSPBCGS and PCILU to solve the momentum eqn matrix and
> HYPRE's AMG and the default ksptype to solve the poisson eqn. Do you ppl think
> this is a good choice? Or is there a better recommendation?
> 
> Thank you.
> 
> Lisandro Dalcin wrote:
> > > On Mon, 23 Jul 2007, Lisandro Dalcin wrote:
> > > I think it's the same that I am using, but I am not sure.  Can you
> > > give me a helpful reference?
> > 
> > You can start here. This paper computes stab. params. using element
> > mat and vecs, but you can also found explicit formulas (look for UGN
> > subindices in formulas)
> > 
> > http://www.mems.rice.edu/TAFSM/PUB_PRE/jALL/j89-CMAME-EBTau.pdf
> > 
> > > I'm currently trying Matt's suggestion (to use MUMPS).  (It seems not
> > > to easy to install MUMPS.)
> > 
> > I istall MUMPS by letting PETSc to download and install it for me.
> > Always worked.
> > 
> > > Anyway, I would like to try your solution as well.  What would I have to
> > > do?
> > 
> > First of all, you should move to the latest PETSc (2.3.3). Next, you
> > have to be able to assemble a matrix of type MATIS. This implies you
> > need to setup a ISLocalToGlobalMapping, by passing to it all local
> > indices of degrees of freedom you have in the local processor.
> > Once you have done this, you should be able to solve in parallel an
> > small problem using PCJACOBI (jacobi, not block-jacobi).
> > 
> > Next, mail me again. Using my preconditioner should then work out of
> > the box. If you can confirm some gains, I would consider it to be
> > added to PETSc.
> > 
> > Regards,
> > 
> > 
> 
>