Use this if you are using igraph from R

The order of the vertices only matters in directed graphs,
where the existence of a directed `(v1, v2)`

edge is queried.

are_adjacent(graph, v1, v2)

`graph` |
The graph. |

`v1` |
The first vertex, tail in directed graphs. |

`v2` |
The second vertex, head in directed graphs. |

A logical scalar, `TRUE`

is a `(v1, v2)`

exists in the
graph.

Other structural queries: `[.igraph`

,
`[[.igraph`

, `adjacent_vertices`

,
`ends`

, `get.edge.ids`

,
`gorder`

, `gsize`

,
`head_of`

, `incident_edges`

,
`incident`

, `is_directed`

,
`neighbors`

, `tail_of`

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)

[Package *igraph* version 1.2.4.1 Index]