[petsc-dev] Parallel Gauss - Seidel

Mark F. Adams mark.adams at columbia.edu
Sun Jun 10 11:47:01 CDT 2012

On Jun 9, 2012, at 7:51 PM, Jed Brown wrote:

> On Sat, Jun 9, 2012 at 6:43 PM, Mark F. Adams <mark.adams at columbia.edu> wrote:
> 1) I need a G-S kernel that takes an IS of indices to process and a flag to process them in forward or reverse order.  How should I proceed to do this.  Should I just clone sor?
> You are going to have several of these index sets?


> You could have a PCSORSetIS(). Probably need to add a MatOp for MatSORIS(). Barry might have other ideas.
> 2) I don't want to use Richardson iterations for G-S.  Should I make a G-S KPS method?  I don't want to take a residual in the iterator (KSP) and if symmetric G-S is requested then it should drive this I think.
> Look at PCApplyRichardson_SOR().
>  SOR does two sweeps in each application; I'm not wild about that because a good way to run G-S in a V(1,1) cycle is to do a forward sweep in pre smoothing and a backward sweep in post smoothing.
> Well, MatSOR() has this flag MatSORType that can specify forward and reverse. You have one PC for the down-smoother and another for the up-smoother, then configure one to be a forward sweep and the other to be reverse.

I can have two sets of ISs and avoid the reverse flag.  I was avoiding that option but now that I think about it it simplifies the control code.

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