isCyclic(G)
This method checks whether a MixedGraph is cyclic, i.e. contains a directed cycle or a cycle on directed edges.
A directed cycle is a cycle in the Digraph constructed from a mixed graph G by identifying all connected components on bidirected and undirected edges. Such a connected component contains either bidirected edges only or undirected edges only.
In the following example, there are no directed cycles.





In the next example, there are no cycles inside the digraph of the mixed graph, but there is a directed cycle after you identify the vertices {1,2} and {3,4}.




This is a similar example as before, but now the vertices {1,2} are connected by an undirected edge and {3,4} by a bidirected edge.





In the following example, there is a cycle on the directed edges that is inside a connected undirected component.

