Locate edge in graph

returns the numeric edge indices, `idxOut`

= findedge(`G`

,`s,t`

)`idxOut`

, for the edges specified
by the source and target node pairs `s`

and `t`

.
The edge indices correspond to the rows `G.Edges.Edge(idxOut,:)`

in
the `G.Edges`

table of the graph. If there are multiple edges
between `s`

and `t`

, then all their indices are
returned. An edge index of `0`

indicates an edge that is not in the
graph.