stokes-iterative Python demo segfaults when using Trilinos

[Johannes Ring]

Running the Python version of the stokes-iterative demo results in a segmentation fault when using the Trilinos backend. Changing "amg" to "default" in line 84, that is

  solver = KrylovSolver("tfqmr", "amg")

makes the demo run fine.

The C++ version works fine with "amg".

[Garth Wells (garth-wells)]

Changing the the preconditioner to ilu, the Python version runs fine. It could be related to the order in which objects are destroyed.

[Garth Wells (garth-wells)]

Placing

    del solver

after

    solver.solve(U.vector(), bb)

does not lead to an error. This points to a destruction order issue.