[igraph] Shortest Path

[Herb Roseman]

I have successfully created a digraph of some sixty vertices.  I am now trying to find shortest paths.  I use the statement

pa = ethics_net.get_shortest_paths(beg_node,end_node)

I am told by the system:

ValueError: no such vertex: '12'.

There is a vertex 12, I created it with this statement:

 ethics_net = igraph.Graph(n =len(sorted_keys), directed = True)

Where have I gone wrong?

As usual, thanks for your excellent help.

Herb