I try to run the demo of singular poisson, but I get the error message "AttributeError: 'KrylovSolver' object has no attribute 'set_nullspace' ''.
Thanks in advance!
The demo is here
The link you posted is for FEniCS 1.3. Singular poisson demo for 2017.1.0: link.
The difference seems to be that in 1.3 the null space was attached to the solver, now you attach it to the matrix.
Thanks for your answer. It works.