1No vertices, not directed:
2No vertices, directed:
3Directed graph with loops and multi-edges with negative loop:
4Directed graph with loops and multi-edges:
5[        0       -1       -3        1        6      Inf
6         1        0       -2        2        7      Inf
7         3        2        0        4        9      Inf
8       Inf      Inf      Inf        0        5      Inf
9       Inf      Inf      Inf      Inf        0      Inf
10       Inf      Inf      Inf      Inf      Inf        0 ]
11Directed graph with loops and multi-edges, select vertices 1 and 2:
12[        0       -2
13         2        0 ]
14Directed graph with loops and multi-edges, select 0 -> 2:
15[       -3 ]
16Directed graph with loops and multi-edges, select none:
17