[petsc-users] two-level Schwarz: PCMG or PCComposite

Barry Smith bsmith at mcs.anl.gov
Fri May 11 07:55:59 CDT 2012

  If this is what you want to do then just use the PCCOMPOSITE. Use PC_COMPOSITE_SYMMETRIC_MULTIPLICATIVE


On May 11, 2012, at 6:26 AM, Hui Zhang wrote:

> I want to implement the two-level Schwarz method.  Let us denote P as the one-level
> Schwarz projection and P_0 as the coarse projection.  If I want the hybrid form of 
> preconditioned system as follows:
>     (I-P_0) P (I-P_0) 
> which is suitable:  PCMG or PCComposite?  It seems to me that PCComposite is good.
> But PCMG is not suitable because it can only implement the following form:
>     (I-P) P_0 (I-P)
> Any opinions?  Thanks!

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