On Thu, Aug 5, 2010 at 9:45 AM, Mark F. Adams <mark.adams at columbia.edu>wrote:
> Jed brings up good points about false negatives, there are also false > positives to worry about. This is a bad idea, at least as a default solver. > > I was not thinking about that at all. There would be no false positives because the user would be required to say "I have exactly this Stokes system, I am just too lazy to make my ISes, please do it for me Magic PETSc". Matt > That said, there is work on "adaptive" solvers like bootstrap AMG and using > machine learning to formalize what it sounds like Barry is driving at. > Perhaps make a '-ksp_type black_box' solver type where you put any > heuristics methods like this. (this would require the KSP method to change > the PC method which is ugly...) > > Mark > > On Aug 5, 2010, at 5:36 AM, Matthew Knepley wrote: > > On Thu, Aug 5, 2010 at 2:10 AM, Jed Brown <jed at 59a2.org> wrote: > >> On Thu, 5 Aug 2010 00:21:13 -0500, Matthew Knepley <knepley at gmail.com> >> wrote: >> > If someone tells us, "I have a Stokes problem", we could search for 0 >> > diagonals and create the partition for FS. >> >> I suppose this would work for some common cases, but there are lot of >> discretizations and pressure-dependent constitutive relations/boundary >> conditions that have nonzeros in the pressure block. I think some slip >> conditions can also produce zero or negative values in the momentum >> block. >> > > Do not disagree. > > >> I'm not convinced that it's so much to ask people to provide an index >> set, considering that FieldSplit is a somewhat advanced thing anyway >> (based on sheer number of choices available, and (typical) sensitivity >> to those choices). > > > I guess the point here is somewhat like the point of DAs. It is a very > limited > thing, but something many people do. So we provide a way to most easily > do the very limited thing. > > Not sure if this is useful enough, but it might be. > > Matt > > >> >> Jed >> > > > > -- > What most experimenters take for granted before they begin their > experiments is infinitely more interesting than any results to which their > experiments lead. > -- Norbert Wiener > > > -- What most experimenters take for granted before they begin their experiments is infinitely more interesting than any results to which their experiments lead. -- Norbert Wiener -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.mcs.anl.gov/pipermail/petsc-dev/attachments/20100805/56a14420/attachment.html>
