On Jun 9, 2012, at 8:26 PM, Jed Brown wrote:
> I think he wants to manage the messages at a higher level and call a matrix
> kernel for the partial sweeps.
>
> I would prefer to write the communication primitives so that GS for each
> matrix format is simple.
I am not sure if this is the right model. But it is an alternative approach.
Do you envision PCApply_SOR() managing all the stages of MPI sends and
receives? Or a new PCApply_PGS() managing that process.
I admit I was thinking the Mat is responsible for its various SORs, but
other alternatives as you propose seem reasonable.
From the user prospective I think it is better not bot have both PCSOR and
PCSPGS but to have options for PCSOR to make it it support PGS. How it is
handled internally with complicated PCApply_SOR or complicated MatSOR_MPIAIJ()
etc is more a detail I am less concerned about.
Barry
>
> On Jun 9, 2012 8:21 PM, "Barry Smith" <bsmith at mcs.anl.gov> wrote:
>
> On Jun 9, 2012, at 8:18 PM, Jed Brown wrote:
>
> > He is going to alternate between smoothing some points and sending messages.
>
> Fine but that is all INSIDE a single SOR sweep? So I was wrong to say
> PCSORSetIS() maps to MatSORSetIS() it is PCSORSSetISs() maps to
> MatSORSetISs() he won't be calling MatSOR() for each piece but ONCE for the
> whole process (yes the MatSOR_SeqAIJ() is more complicated in this case.
>
> Barry
>
> >
> > On Jun 9, 2012 8:07 PM, "Barry Smith" <bsmith at mcs.anl.gov> wrote:
> >
> > On Jun 9, 2012, at 8:01 PM, Jed Brown wrote:
> >
> > > Parallel Gauss-Seidel.
> >
> > But if you know in advance the IS that you are providing (that determines
> > the order of the nodes smoothed) then why would you change it the next
> > iteration? That is, if you are providing the IS then it is in no way
> > asynchronous so that the fact that it is "parallel" Gauss-Seidel doesn't
> > affect the ordering. Hence I consider your response humorous but non
> > responsive :-)
> >
> > Barry
> >
> >
> >
> >
> > >
> > > On Jun 9, 2012 7:56 PM, "Barry Smith" <bsmith at mcs.anl.gov> wrote:
> > >
> > > On Jun 9, 2012, at 7:47 PM, Jed Brown wrote:
> > >
> > > > Fine, but I think Mark is going to change the IS every time MatSOR is
> > > > called.
> > >
> > > Surely not. What kind of weird-ass algorithm would that be?
> > >
> > > Barry
> > >
> > > > Either will work, but a separate call is awkward if it's not useful to
> > > > be persistent.
> > > >
> > > > On Jun 9, 2012 7:45 PM, "Barry Smith" <bsmith at mcs.anl.gov> wrote:
> > > >
> > > > On Jun 9, 2012, at 6:51 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.
> > > >
> > > > PCSORSetIS() would then go down to MatSORSetIS() and then the call to
> > > > MatSOR() would using the IS ordering if provided, otherwise use the
> > > > default natural ordering?
> > > >
> > > > I don't see a need to add a MatSORIS().
> > > >
> > > > Barry
> > > >
> > > >
> > > > >
> > > > > 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.
> > > >
> > >
> >
>
