The order of the vertices only matters in directed graphs, where the existence of a directed (v1, v2) edge is queried.

(v1, v2)

are_adjacent(graph, v1, v2)

The graph.

The first vertex, tail in directed graphs.

The second vertex, head in directed graphs.

A logical scalar, TRUE is a (v1, v2) exists in the graph.

TRUE

Other structural queries: [.igraph, [[.igraph, adjacent_vertices, ends, get.edge.ids, gorder, gsize, head_of, incident_edges, incident, is_directed, neighbors, tail_of

[.igraph

[[.igraph

adjacent_vertices

ends

get.edge.ids

gorder

gsize

head_of

incident_edges

incident

is_directed

neighbors

tail_of

# NOT RUN { ug <- make_ring(10) ug are_adjacent(ug, 1, 2) are_adjacent(ug, 2, 1) dg <- make_ring(10, directed = TRUE) dg are_adjacent(ug, 1, 2) are_adjacent(ug, 2, 1) # }

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