Using PETSc in structured c-grid for CFD and multigrid

[Ben Tay]

Hi,

just to clarify. I'm using structured grid but not cartesian ie strictly
horizontal/vertical. So I can't DA, can I?

But can I use DMMG? So PETSc comes with a multigrid preconditioner and
solver?

Thank you


On 1/26/07, Matthew Knepley <knepley at gmail.com> wrote:
>
> On 1/25/07, Ben Tay <zonexo at gmail.com> wrote:
> >
> > Hi,
> >
> > I was discussing with another user in another forum (cfd-online.com)
> > about using PETSc in my cfd code. I am now using KSP to solve my momentum
> > and poisson eqn by inserting values into the matrix. I was told that using
> > PETSc this way is only for unstructured grids. It is very inefficient and
> > much slower if I'm using it for my structured grid because I am not
> > exploiting the regular structure of my grid.
> >
> > Is that true? I'm solving flow around airfoil using c-grid.
> >
>
> If you are using a Cartesian grid, the  DA  formulation is better.
> However, this nonsense from people about
> "massive  inefficiency"  is just crap. There is a small difference in time
> which is almost trivial. However, there
> is a big difference in ease of programming. I am always fascinated how
> people can magnify small problems
> in order to preserve their job.
>
>
>  So how can I improve? Is it by using DA? I took a glance and it seems
> > quite complicated.
> >
>
> Wrong glance. Much simpler.
>
>
>  Also, is multigrid available in PETSc? Chapter 7 discusses about it but
> > it seems very brief. Is there a more elaborate tutorial besides that c
> > examples?
> >
>
> Yes, use DMMG. Much easier with DA.
>
>   Matt
>
>
>  Hope someone can give me some ideas.
> >
> > Thank you.
> >
> >
> >
>
>
>
> --
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> and critically is forced to realize that there are scarcely any bars to
> eventual
> publication. There seems to be no study too fragmented, no hypothesis too
> trivial, no literature citation too biased or too egotistical, no design
> too
> warped, no methodology too bungled, no presentation of results too
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> and
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> Drummond Rennie
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