Hi petsc team, I have a question about using nested matrices and vectors for coupled solution of Stokes system with filedsplit preconditioner.
Is there a simple example explaining how I can create nested matrix and vector using "MatCreateNest" and "VecCreateNest" functions, provided that I already have all constituting blocks correctly assembled? I could not find these example online, and if I do it straightforwardly according to documentation, petsc complains that some vector blocks are not setup. Do I need to define velocity and pressure splits using "PCFieldSplitSetIS", because if I don't, petsc says "Unhandled case, must have at least two fields, not 1!"? Do I need to explicitly specify the blocksize, if I want to use the filedsplit preconditioner for the velocity block? A small example would be extremely helpful Thanks a lot, Anton
