> On 12 Mar 2020, at 11:40 PM, Matthew Knepley <[email protected]> wrote: > > On Thu, Mar 12, 2020 at 5:59 PM Jed Brown <[email protected] > <mailto:[email protected]>> wrote: > Pierre Jolivet <[email protected] > <mailto:[email protected]>> 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> > > <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. > 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> > > <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/>
