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

[Hui Zhang]

On May 11, 2012, at 2:55 PM, Barry Smith wrote:

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

Aha, I see.  Thank you, Barry!  
Just one more question on PCCompositeAddPC:  is firstly added PC also firstly applied,
i.e. the order of applying PC's is the same as the order of PCCompositeAddPC ?

> 
> 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!
>> 
>> 
> 
>