Dear Firedrakers, I use utility meshes, including the extruded ones. I need to access the entries of system matrices, but I am not sure about the node/entries numbering. Say, I have the code: m = UnitIntervalMesh(3) mesh = ExtrudedMesh(m, 3) V = FunctionSpace(mesh, "CG", 1) f = Function(V) trial = TrialFunction(V) test = TestFunction(V) A = assemble( trial * test * dx ).M.values Does the element A[i,j] correspond to nodes mesh.coordinates.dat.data[i] & [j], same as f.dat.data[i] & j? What is the case for VectorFunctionSpace? Thanks, Tomasz