Are two vertices adjacent?

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

Usage

are_adjacent(graph, v1, v2)

Arguments

graph

The graph.

v1

The first vertex, tail in directed graphs.

v2

The second vertex, head in directed graphs.

Value

A logical scalar, TRUE if edge (v1, v2) exists in the graph.

See also

Other structural queries: [.igraph(), [[.igraph(), adjacent_vertices(), ends(), get_edge_ids(), gorder(), gsize(), head_of(), incident(), incident_edges(), is_directed(), neighbors(), tail_of()

Related documentation in the C library

igraph_are_adjacent().

Examples

ug <- make_ring(10)
ug
#> IGRAPH fbcfb31 U--- 10 10 -- Ring graph
#> + attr: name (g/c), mutual (g/l), circular (g/l)
#> + edges from fbcfb31:
#>  [1] 1-- 2 2-- 3 3-- 4 4-- 5 5-- 6 6-- 7 7-- 8 8-- 9 9--10 1--10
are_adjacent(ug, 1, 2)
#> [1] TRUE
are_adjacent(ug, 2, 1)
#> [1] TRUE

dg <- make_ring(10, directed = TRUE)
dg
#> IGRAPH fd1f58e D--- 10 10 -- Ring graph
#> + attr: name (g/c), mutual (g/l), circular (g/l)
#> + edges from fd1f58e:
#>  [1]  1-> 2  2-> 3  3-> 4  4-> 5  5-> 6  6-> 7  7-> 8  8-> 9  9->10 10-> 1
are_adjacent(ug, 1, 2)
#> [1] TRUE
are_adjacent(ug, 2, 1)
#> [1] TRUE