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. > > >
