2.4. igraph_average_path_length — Calculates the average geodesic length in a graph.

int igraph_average_path_length(const igraph_t *graph, igraph_real_t *res,
			       igraph_bool_t directed, igraph_bool_t unconn);

Arguments:

`graph`:	The graph object.
`res`:	Pointer to a real number, this will contain the result.
`directed`:	Boolean, whether to consider directed paths. Ignored for undirected graphs.
`unconn`:	What to do if the graph is not connected. If `TRUE` the average of thr geodesics within the components will be returned, otherwise the number of vertices is used for the length of non-existing geodesics. (The rationale behind this is that this is always longer than the longest possible geodesic in a graph.)

Returns:

Error code: IGRAPH_ENOMEM, not enough memory for data structures

Time complexity: O(|V||E|), the number of vertices times the number of edges.