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

[Alp Kalpalp]

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

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?

Thanks again and merry christmas to all



On Sun, Dec 28, 2014 at 4:28 PM, Mark Adams <mfadams at lbl.gov> wrote:

>
>
> On Sat, Dec 27, 2014 at 5:00 AM, Alp Kalpalp <alpkalpalp at gmail.com> wrote:
>
>> Hi,
>>
>> I implemented a newmark time stepping algorithm without using TS
>> structure. I am following ex59 about PCBDDC.
>>
>>
> use TS
>
>
>> ComputeMatrix
>> ComputeKSPBDDC
>>
>> for // a time loop
>> {
>> Compute RHS
>> KSPSolve
>> GatherResults
>> MoveToNextTS
>> }
>>
>>
>> However, when I watch the iteration counts of KSPSolve they do not
>> decrease signicantly..Decrease was around 5%.
>>
>> So I have some problems;
>>
>> 1-) I guess currently, factorization is not taking place for each time
>> step in my code. Ok this is expected. But I wonder whether Kspsolve stores
>> the Krylov subspace vectors and reuse them for the next time step.
>>
>>
> No.  Certainly not by default.
>
>
>> 2-) PCBDDC uses KSPCG and AFAIK petsc doesnot have preconditioned
>> conjugate projected gradient (PCPG). Is it possible to simulate PCPG
>> iteration in some way?
>>
>>
> KSP has a PC object and all methods use it AFAIK.
>
>
>> Thanks,
>>
>>
>>
>
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