[petsc-users] no decrease in iteration counts of KSPCG during time stepping

[Umut Tabak]

On 12/28/2014 05:54 PM, Alp Kalpalp wrote:
> Hi,
>
> Thank you Mark.
>
> Let me clarify my questions;
>
> 1-)How to implement or activate a Reorthogonalization procedure for 
> KSPCG..
> As you know, search directions can be found more rapidly (with less 
> numer of iterations) by using previous successive directions
Without answering the PETSc related questions, interesting discussion,

indeed, but at the cost of purging the previous directions(which means 
explicit orthogonalizations with respect to these vectors also), so I am 
not sure if you can gain something with this, cost wise...
>
> 2-) How to implement or activate a projection space over CG. A sample 
> projection can be;
> P = I - G*((G'*G)\G').
> I need to insert project,scale,precondition,re-scae,re-project steps 
> during each KSPCG iteration. How can I utilize this?
>
Just a side note, I had previous experience on this that these kinds of 
practice increase the cost more...
BR,
Umut
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