[petsc-users] V-cycle multigrid with matrix shells

[Jed Brown]

On Thu, May 12, 2011 at 08:12, Sylvain Barbot <sylbar.vainbot at gmail.com>wrote:

> My primary concern now is computation speed, especially for
> 3-D problems, where i have of the order 512^3 degrees of freedom. I
> was planning to test Jacobi and SOR smoothers. Is there another
> smoother you recommend for this kind of problem?
>

It's worth trying ILU as a smoother, especially if you are using a stretched
mesh. What discretization are you using? I still recommend just writing the
matrix assembly and experimenting (you can do everything on the command
line). Then, if the problem of interest responds well to SOR, you can easily
put in an option to use matrix-free. That is, you would have one code with a
runtime option of which levels to assemble versus handle matrix-free. The
fastest choice will almost certainly depend on the problem and on the
hardware that you are running it on, so it's well worth having both options
available.
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