I have tried to apply the bddc and multigrid preconditioners to the Stokes problem, discretised Taylor-Hood elements.
Unfortunately I have come across the following issues,
[li]BDDC with GMRes: The pressure error stops converging after some mesh refinements, even with a very small tollerance and a large number of gmres iterations. A direct solver on the other hand gives pressures which continue to converge.
[li] Multigrid with static condensation: Numeric factorization fails when the matrix is assembled (this did not happen on a Poission example).
[li] Multigrid without static condensation: Segfault see
Can anyone help me with these problems?