[petsc-users] Composite shell preconditiner

Alexander Grayver agrayver at gfz-potsdam.de
Fri Aug 17 09:42:21 CDT 2012


I do see the drawbacks of this method, but it seems to have good 
That I want to test.

Thank you.

On 17.08.2012 16:32, Jed Brown wrote:
> On Fri, Aug 17, 2012 at 9:23 AM, Alexander Grayver 
> <agrayver at gfz-potsdam.de <mailto:agrayver at gfz-potsdam.de>> wrote:
>     Right.
>     Could you please explain what do you mean by fragile?
> Fragile means unreliable. The math is not right for Krylov methods in 
> general. You are relying on side-effects of particular methods and 
> preconditioner side combinations. Fragile is the opposite of "robust". 
> For a "robust" method, you should start with a compatible 
> discretization and/or choose a preconditioner that is stable on the 
> quasi-null space and/or filter in a way that is consistent with the 
> Krylov method (e.g. as described using FGMRES).
>>         Looks a bit tricky. The number of fgmres iterations then
>>         defines number of the cycles correction will be applied,
>>         doesn't it?
>>     Yes.
>     If I do this command line only setup:
>     -pc_type composite -pc_composite_type multiplicative
>     -pc_composite_pcs ksp,shell
>     How does petsc know what ShellPCApply routine to take? I guess I
>     have to specify this in the code anyway?
> Yeah, to select your preconditioner in this way, you should name it 
> preconditioner something meaningful and use PCRegisterDynamic() just 
> like the native implementations.


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