SKEDSOFT

ORIENTATION OF A GRAPH: Given a graph G, if there is a digraph D such that G is the underlying graph of D then D is called an orientation of G.
The digraphs in Fig. 8.1(b) and Fig. 8.1(c) are two different orientations of the graph in Fig. 8.1(d).

UNDERLYING GRAPH
If D is a digraph, the graph obtained from D by ‘removing the arrows’ from the directed edges is called the underlying graph of D. This graph is also called the undirected graph corresponding to D.
The underlying graph of the digraph in Fig. 8.1(b) is shown in Fig. 8.1(d).
The graph in Fig. 8.1(d) is the underlying graph of the digraph shown in Fig. 8.1(c).

Note : Every digraph has a unique underlying graph.