Line graph: Difference between revisions

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* If a graph {{mvar|G}} has an [[Euler cycle]], that is, if {{mvar|G}} is connected and has an even number of edges at each vertex, then the line graph of {{mvar|G}} is [[Hamiltonian graph|Hamiltonian]]. However, not all Hamiltonian cycles in line graphs come from Euler cycles in this way; for instance, the line graph of a Hamiltonian graph {{mvar|G}} is itself Hamiltonian, regardless of whether {{mvar|G}} is also Eulerian.<ref>{{harvtxt|Harary|1972}}, Theorem 8.8, p.&nbsp;80.</ref>
* If two simple graphs are [[graph isomorphism|isomorphic]] then their line graphs are also isomorphic. The [[Graph isomorphism#Whitney theorem|Whitney graph isomorphism theorem]] provides a converse to this for all but one pair of graphs.
* In the context of complex network theory, the line graph of a random network preserves many of the properties of the network such as the [[Small-world network|small-world property]] (the existence of short paths between all pairs of vertices) and the shape of its [[degree distribution]].{{sfnp|Ramezanpour|Karimipour|Mashaghi|2003}} {{harvtxt|Evans|''L''ambiotteLambiotte|2009}} observe that any method for finding vertex clusters in a complex network can be applied to the line graph and used to cluster its edges instead.
 
===Whitney isomorphism theorem===