Hi, thank you for the SfePy. I wish to apply SfePy in my research project, but I'm now having a few problems. I want to get the stiffness matrix for postprocessing by my self. The pb (Problem) object has an attribute namely mtx_a, is it the stiffness matrix I'm looking for? If so, I get some puzzles: in my view, after "pb = Problem('name',equations=eqs)" and "pb.set_bcs", the problem has been already clearly defined. But so far the pb.mtx_a is still a non-type object and I can get the pb._mtx_a only after "pb.set_solver(nls)", "pb.solve()". I believe the stiffness matrix is determined only by the problem itself and corresponding essential boundary conditions, not including the solvers. So could you please tell me why is that, or where can I find the proper stiffness of the problem? Looking forward for your answers, and thank you again for this wonderful project!