[petsc-users] Advice Being Sought

[Tahar Amari]

Hello Matt,

I am not sure I understand your point.
I guess you  mean that inside petsc only  a version of Gmres working with preconditioning is not  yet implemanted , Am I right ?

Tahar
Le 22 avr. 2013 à 14:12, Matthew Knepley a écrit :

> On Mon, Apr 22, 2013 at 7:56 AM, David Scott <d.scott at ed.ac.uk> wrote:
> Hello,
> 
> I am working on a fluid-mechanical code to solve the two-phase Navier–Stokes equations with levelset interface capturing. I have been asked to replace the pressure calculation which uses the SOR and Jacobi iterative schemes with a Krylov subspace method. I have done this and the code is working but as I have never used PETSc before I would like to know if improvements to my code, or the run time parameters that I am using, could be made.
> 
> I am using GMRES with a Block Jacobi pre-conditioner. I have tried Conjugate Gradient with a Block Jacobi pre-conditioner but it diverges. If I use GMRES for the first few thousand time steps and then swap to CG it does converge but the speed of execution is somewhat reduced.
> 
> Krylov methods do not work with preconditioners. You have a Poisson problem, so as abundantly documented in the literature, you should use multigrid. The easiest thing to try is
> 
>   -pc_type gamg -pc_gamg_agg_nsmooths 1
> 
>    Thanks,
> 
>      Matt
>  
> I have attached relevant excerpts from the code.
> 
> Yours sincerely,
> 
> David Scott
> -- 
> Dr. D. M. Scott
> Applications Consultant
> Edinburgh Parallel Computing Centre
> Tel. 0131 650 5921
> 
> The University of Edinburgh is a charitable body, registered in
> Scotland, with registration number SC005336.
> 
> 
> 
> -- 
> What most experimenters take for granted before they begin their experiments is infinitely more interesting than any results to which their experiments lead.
> -- Norbert Wiener

--------------------------------------------
T. Amari
Centre de Physique Theorique
Ecole Polytechnique
91128 Palaiseau Cedex France
tel : 33 1 69 33 42 52
fax: 33 1 69 33 49 49
email: <mailto:tahar.amari at polytechnique.edu>
URL : http://www.cpht.polytechnique.fr/cpht/amari





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