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.
