Tuning the bddc preconditioner

Hi,

I have a symmetric indefinite matrix to solve,
K = [A, B]
[B^T -S].
Minres with a block diagonal preconditioner
M = [A^{-1} 0]
[0, S^{-1}]
works quite well for this particular system.

Here A is roughly a (h.o.) mass matrix and S is the diffusion operator.
I was wondering if the bddc preconditioner can be separately applied to the sub matrices A and S, instead of directly on the big matrix K by default?

Also, how can I change the coarsetype in bddc to other solvers like the ones in the petsc library?

Best regards,
Guosheng

I was wondering if the bddc preconditioner can be separately applied to the sub matrices A and S, instead of directly on the big matrix K by default?

You could set up two seperate bddc preconditioners and then use BlockMatrix.

Also, how can I change the coarsetype in bddc to other solvers like the ones in the petsc library?

This does not currently work with the PETSc interface, sorry.

Best,
Lukas

How to apply bddc to submatrices? Do I need to create separate bilinear forms for each block, or can I directly work with the big bilinear form by providing the active dofs?
Here is a minimal code:

You need separate BilinearForms.