For undirected graphs, head and tail is not defined. In this case
tail_of() returns vertices incident to the supplied edges, and
head_of() returns the other end(s) of the edge(s).
See also
Other structural queries:
[.igraph(),
[[.igraph(),
adjacent_vertices(),
are_adjacent(),
ends(),
get_edge_ids(),
gorder(),
gsize(),
head_of(),
incident(),
incident_edges(),
is_directed(),
neighbors()
