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).
tail_of(graph, es)
The input graph.
The edges to query.
A vertex sequence with the tail(s) of the edge(s).
Other structural queries: [.igraph
;
[[.igraph
; adjacent_vertices
;
are.connected
, are_adjacent
;
ecount
, gsize
;
ends
, get.edge
,
get.edges
; get.edge.ids
;
gorder
, vcount
;
head_of
; incident_edges
;
incident
; is.directed
,
is_directed
; neighbors