Do direct methods preserve the non-zero pattern of the system matrix? Do they preserve any particular structure?

After applying a MattLab code these are the plots that I get, How can I interpret them in order to answer the questions?

0 0 20F. 30 40 50 60 40 50 60 30 nz = 240 10 20 0 10 40 60 60 0 20 20 40 nz 541 0 nz = 541