[petsc-dev] Unions of IS and MatNest

[Jed Brown]

Pierre Jolivet <pierre.jolivet at 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?

> 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.