1.1. igraph_are_connected — Decides whether two vertices are connected

int igraph_are_connected(const igraph_t *graph, 
			 igraph_integer_t v1, igraph_integer_t v2,
			 igraph_bool_t *res);

Arguments:

`graph`:	The graph object.
`v1`:	The first vertex.
`v2`:	The second vertex.
`res`:	Boolean, `TRUE` if there is an edge from `v1` to `v2`, `FALSE` otherwise.

Returns:

Error code.

The function is of course symmetric for undirected graphs.

Time complexity: O(d), d is the out-degree of v1.