No vertices, not directed:
No vertices, directed:
Directed graph with loops and multi-edges with negative loop:
Directed graph with loops and multi-edges:
[        0       -1       -3        1        6      Inf
         1        0       -2        2        7      Inf
         3        2        0        4        9      Inf
       Inf      Inf      Inf        0        5      Inf
       Inf      Inf      Inf      Inf        0      Inf
       Inf      Inf      Inf      Inf      Inf        0 ]
Directed graph with loops and multi-edges, select vertices 1 and 2:
[        0       -2
         2        0 ]
Directed graph with loops and multi-edges, select 0 -> 2:
[       -3 ]
Directed graph with loops and multi-edges, select none: