But what does using B as 00 block actually mean? It seems to me that you pivot, producing P' P J where P J has B in the 00 location. On Mar 23, 2012 6:13 PM, "Barry Smith" <bsmith at mcs.anl.gov> wrote:
> > On Mar 23, 2012, at 6:00 PM, Jed Brown wrote: > > > On Fri, Mar 23, 2012 at 17:48, Barry Smith <bsmith at mcs.anl.gov> wrote: > > I'm confused. I am NOT injecting it into the original definition, I > am injecting it into the PCFieldSplit in the same way that your > "permutation" would inject it just into the PCFieldSplit, it is just (in my > opinion) a more user friendly way of the user providing this permutation. > Note that this "two fields" business is NOT going in the DM (and hence into > the original definition of the problem) and would normally only be used > when the DM definition was "bad" (due to zero block for example) just like > your permutation would only be used when things were bad. > > > > 1. The PCFieldSplitSetIS() interface does not have this. > > > > 2. The reason for pivoting is not that the DM ordering was "bad", it's > that a symmetric ordering without the 0 block does not exist (factorization > does not work with _any_ symmetric ordering). So you pivot for > factorization and restore. > > I don't agree. Consider [A B ; C D] where all four matrices are > square and non-singular. It may be that using B as the 00 block is just > better for convergence etc > > > > > 3. You now have one name for a set of rows and columns that may not "go > together". > > That name is only for setting fieldsplit options etc. It is not > fieldnames in the way that DM fieldnames are names of fields. > > > > > Somehow I think this is just more confusing and less run-time-friendly, > but maybe that's my fault. In any case, the change has to be consistent > (PCFieldSplitSetIS) and we have to decide how the DM can specify when > pivoting is needed. > > You may be right. Spec out your alternative Functions I would call and > command line options I would use to get the same effect as the affect > Jungho and I were trying to achieve. I was bothered by the separation in > your original proposal between the > selection of the blocks the "pivoting" of your model. I don't really see > using a different block in 00 as necessarily a "pivoting" that is why you > proposal turned me off. > > > Barry > > > -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.mcs.anl.gov/pipermail/petsc-dev/attachments/20120323/0591b777/attachment.html>
