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Line GraphIn graph theory, the line graph L(G) of a graph G is a graph such that - each vertex of L(G) represents an edge of G; and
- any two vertices of L(G) are adjacent if and only if their corresponding edges are incident, meaning they share a common endvertex, in G.
A line graph L(G) can easily be constructed from any graph by - . Create a vertex in L(G) for each edge of G
- . For each vertex in L(G), add an edge to all of its neighbors -- all the other vertices corresponding to edges in G that touch the vertex at either end of the edge in G.
Some graphs are not a line graph. For example, the graph * | | *--*--* \ | / \|/ * is not a line graph of any other graph. The line graph of the above graph is * /|\ / | \ *--|--* |\ | /| | \|/ | | * | | / \ | |/ \| *-----* Properties
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