Dear,
First two answers are appreciated;
?
And last one is more appreciated;
-mg_levels_1_ksp_type cg can this be written in routine ? yes, with
KSPSetType() but which ksp-context ? ksp_pre ?
My Preconditioner:
I? need a preconditioner which read as: Prec = \lambda_max*C + (I - AC) , [C =
CGC] where (I - AC) deflates spectrum to zero,
and this part \lambda_max *C then shifts spectrum to \lambda_max (which is
always 1 in my case) .
Dont I get my Prec by multiplicative combination of CGC with post smoother S =
Identity? using mg_type_multiplicative?
Thanks in anticipation,
regards, Abdul multiplicative_
>________________________________
>I dont want to try snes, since my problem is linear,
>
>
>Note that you can still use SNES for linear problems. (I prefer the interface,
>you can choose -snes_type ksponly so there is no extra overhead, but use
>whatever you like.)
>Thanks!
>
>but I successfully applied the KSP
>>preconditioned with PCMG (not kaskade, but multiplicative; for some reasons) .
>>I make pre-smoother dummy by setting KSP_PRE context as? PREONLY alongwith
>>PCNONE.
>>
>
>
>You can just set the number of pre-smoothing steps to 0.
>?Done! :-)
>
>CGC and post-smoother serves my purpose to apply preconditioner
>>Prec = I - A*P*(A_H)^-1 * R?? with KSP_POST as RICHARDSON alongwith PCNONE.
>>
>
>
>Read my last message again. You either want the additive
>
>
>Prec = I + C
>
>
>(where C = P*A_H^{-1}*R is the coarse solve)?or the multiplicative
>
>
>Prec = C + S (I - A C)
>
>
>perhaps with S = I (or some scaling factor). I don't think your definition of
>Prec makes sense or is the operation that you intend to be applying.
>
>
>I hope PCNONE make smoother S = I in the framework you suggested earlier i.e.
>>
>>C b + S (b - A C b)~~~~~~ where C is read as CGC.
>>
>>It seems working well with levels 2, but when I force RICHARDSON_max_it 0. To
>>my understanding, it should work with RICHARDSON_max_it = 1;?
>
>
>Read through my last message again. I explained that this does not work and
>that it is caused by the destabilizing effect of the extra multiply without a
>smoother. You can fix it for easy problems with
>-mg_levels_ksp_richardson_self_scale.
>?
>What if I want to approximate my all coarse matrices with any Krylov iteration
>?
>
>
>The methods on each level are independent, you can set them with
>-mg_coarse_ksp_type gmres -mg_levels_1_ksp_type cg -mg_levels_1_ksp_max_it 100
>-mg_levels_2_ksp_type minres ...?
>
>
>
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