Use this if you are using igraph from R
Incident vertices of some graph edges
ends(graph, es, names = TRUE)
| graph | The input graph | 
| es | The sequence of edges to query | 
| names | Whether to return vertex names or numeric vertex ids. By default vertex names are used. | 
A two column matrix of vertex names or vertex ids.
Other structural queries: [.igraph,
[[.igraph, adjacent_vertices,
are_adjacent, get.edge.ids,
gorder, gsize,
head_of, incident_edges,
incident, is_directed,
neighbors, tail_of
g <- make_ring(5) ends(g, E(g))