Use this if you are using igraph from R

are_adjacent {igraph} | R Documentation |

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 1.3.2 Index]