On Fri, Mar 13, 2020 at 3:19 AM Pierre Jolivet <pierre.joli...@enseeiht.fr> wrote:
> > > On 12 Mar 2020, at 11:40 PM, Matthew Knepley <knep...@gmail.com> wrote: > > On Thu, Mar 12, 2020 at 5:59 PM Jed Brown <j...@jedbrown.org> wrote: > >> Pierre Jolivet <pierre.joli...@enseeiht.fr> writes: >> >> > Hello, >> > Has there been any follow-up on this >> https://lists.mcs.anl.gov/pipermail/petsc-users/2015-January/024020.html >> <https://lists.mcs.anl.gov/pipermail/petsc-users/2015-January/024020.html >> >? >> > Given a 3x3 MatNest A = [A_00,0,0 ; 0,A_11,0 ; 0,0,A_22], I’d like to >> setup a two-way fieldsplit coupling [A_00,0 ; 0,A_11] and [A_22] but I >> can’t figure out the proper options. >> >> Are you looking for a Schur split or additive/multiplicative? > > > Don’t know yet which will perform best, do you have a specific solution in > mind for one scenario or the other? > I was mostly wondering if it was possible in a general context, not taking > -pc_fieldsplit_type into account. > > -pc_fieldsplit_field_0 0,1 -pc_fieldsplit_field_1 2 -pc_fieldsplit_type > schur > > > These flags, used with my .cpp, yield: > [0]PETSC ERROR: Arguments are incompatible > [0]PETSC ERROR: To use Schur complement preconditioner you must have > exactly 2 fields > If I use -pc_fieldsplit_%d_fields <a,b,..> as advocated in the manual > (instead of -pc_fieldsplit_field_%d as you suggested), I get the same error. > Okay it is -pc_fieldsplit_%d_fields. When you use this, how many fields does it think you have? Matt > I believe. > > Matt > > >> > Jed, in this answer >> https://lists.mcs.anl.gov/pipermail/petsc-users/2015-January/023993.html >> <https://lists.mcs.anl.gov/pipermail/petsc-users/2015-January/023993.html>, >> you recommend not to use MatNest. What would you recommend instead? >> >> See src/snes/examples/tutorials/ex28.c for my preferred approach. > > > I’m not using DM, so in terms of Mat, I guess this example shows that I > pretty much need to reimplement the field splitting myself? > > Thanks, > Pierre > > -- > 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 > > https://www.cse.buffalo.edu/~knepley/ > <http://www.cse.buffalo.edu/~knepley/> > > > -- 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 https://www.cse.buffalo.edu/~knepley/ <http://www.cse.buffalo.edu/~knepley/>
