[Dune-devel] Segmentation fault in dune-istl FastAMG with gamma=2

[Simon Praetorius]

Hi,

I was playing around with the dune-istl AMG solvers and some smoothers
and parameters for a simple FEM discretization of a poisson equation and
get a segmentation fault (in dune-2.6), or a `std::bad_weak_ptr`
exception (in the latest git version) when using Amg::FastAMG with all
default parameters except gamma=2 (W-cycle). The solver `Amg::AMG` works
fine with this parameter. Should this work also for FastAMG and I just
do something wrong, or is this a bug?

Some detail information:
- Sequential computation
- Solver BiCGSTABSolver with FastAMG as preconditioner
- Matrix = BCRSMatrix<FieldMatrix<double, 1, 1>>
- Criterion =
Amg::CoarsenCriterion<Amg::UnSymmetricCriterion<Matrix,Amg::FirstDiagonal>>
- Amg::Parameters::gamma == 2
- The matrix is assembled in symmetric form, but Dirichlet boundary
conditions are inserted unsymmetrically (by zeroing lines in the matrix)
- I don't know whether this is relevant

The error occurs in (dune-git) hierarchy.hh:173
LevelIterator::increment() where the weak_ptr is converted into a
shared_ptr.

Best wishes,
Simon