understanding the output from -info

[Barry Smith]

On Mon, 12 Feb 2007, Ben Tay wrote:

> Hi,
> 
> I have some questions regarding the use of hypre/boomeramg:
> 
> 1. Is there anything I need to change in the assembly of matrix etc besides
> adding  -pc_type hypre -pc_hypre_type boomeramg ?

   No
> 
> 2. Can it work in a sequential code?

   yes
> 
> 3. I have 2 eqns to solve - momentum and poisson. if I used the options,
> will both equations be solved using hypre?

  yes

>  Can I select which solver to
> solve with which equation?

  yes. For each KSP call KSPSetOptionsPrefix() for example 
KSPSetOptionsPrefix(kspmo,"momentum); KSPSetOptionsPrefix(ksppo,"poisson");
then from the command line use -momentum_ksp_type gmres -poisson_ksp_type cg
-momentum_pc_type lusomething etc. For any solver option.

   Barry

> 
> Thank you.
> 
> 
> On 2/12/07, Barry Smith <bsmith at mcs.anl.gov> wrote:
> >
> >
> > hypre/boomeramg may be the way to go, especially for the Poisson
> > problem. -pc_type hypre -pc_hypre_type boomeramg (-help for lots of
> > tuning options.).
> >
> >   Barry
> >
> >
> > On Sun, 11 Feb 2007, Ben Tay wrote:
> >
> > > Well,
> > >
> > > I am simulating unsteady flow past a moving airfoil at Re~10^4. I'm
> > using
> > > fractional step FVM, which means that I need to solve a momentum and
> > poisson
> > > equation.
> > >
> > > To reach a periodic state takes quite a few hours and so I'm trying to
> > find
> > > ways to speed up the process. I thought parallelizing the code would
> > help
> > > but it seems like it's not the case.
> > >
> > > I'm now trying out different types of solver/preconditioner available on
> > > PETSc to assess their performance. Is there other external solvers,
> > which
> > > PETSc interfaces, which are recommended? I'm thinking of using multigrid
> > to
> > > solve the poisson eqn... wonder if hypre/BoomerAMG etc would help...
> > >
> > >
> > > On 2/11/07, Lisandro Dalcin <dalcinl at gmail.com> wrote:
> > > >
> > > > On 2/10/07, Ben Tay <zonexo at gmail.com> wrote:
> > > > > In other words, for my CFD code, it is not possible to parallelize
> > it
> > > > > effectively because the problem is too small?
> > > > >
> > > > > Is these true for all parallel solver, or just PETSc? I was hoping
> > to
> > > > reduce
> > > > > the runtime since mine is an unsteady problem which requires many
> > steps
> > > > to
> > > > > reach a periodic state and it takes many hours to reach it.
> > > >
> > > > Can you describe your specific application and how are you solving it?
> > > > As Barry said, your need-for-speed is not likely to be solved by
> > > > running in parallel.
> > > >
> > > >
> > > > --
> > > > Lisandro Dalcín
> > > > ---------------
> > > > Centro Internacional de Métodos Computacionales en Ingeniería (CIMEC)
> > > > Instituto de Desarrollo Tecnológico para la Industria Química (INTEC)
> > > > Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET)
> > > > PTLC - Güemes 3450, (3000) Santa Fe, Argentina
> > > > Tel/Fax: +54-(0)342-451.1594
> > > >
> > > >
> > >
>