[petsc-users] ASM for Saddle-point problems

[Adriano Côrtes]

Dear all,

I'm solving a saddle-point problem coming from a 2d stokes problem
discretized by an inf-sup stable mixed element.
By now I'm playing in serial, because I want to understand the
behavior of the solver. I have the whole matrix assembled in memory.
After playing with GMRES and ILU with different fill-ins, I started
playing with ASM to see if I can get better results. By using
-pc_asm_blocks and -pc_asm_overlap  I tried some variations none
giving better results.

My questions are

1. how the blocks are built by PETSc, since my problem is a saddle-point one?
2. From the theoretical point-of-view, block-factorizations, that is
using PCFieldsplit, are in general the best we can have in terms of
performance (number of iterations and scalability)?

Thanks.
Adriano.