Using PETSc in structured c-grid for CFD and multigrid

[Matthew Knepley]

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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