This function calculates the line graph of another graph.
Usage
line.graph(graph)
Arguments
graph
The input graph, it can be directed or undirected.
Value
A new graph object.
concept
Line graph
Details
The line graph L(G) of a G undirected graph is defined as
follows. L(G) has one vertex for each edge in G and two
vertices in L(G) are connected by an edge if their
corresponding edges share an end point.
The line graph L(G) of a G directed graph is slightly
different, L(G) has one vertex for each edge in G and two
vertices in L(G) are connected by a directed edge if the target
of the first vertex's corresponding edge is the same as the source of
the second vertex's corresponding edge.