Line Graph
A Line Graph 
(also called an Interchange Graph) of a graph 
is obtained by associating avertex with each edge of the graph and connecting two vertices with an edge Iff the corresponding edges of meet at one or both endpoints. In the three examples above, the original graphs are the Complete Graphs 
, 
, and 
shown in gray, and their line graphs are shown in black.
References
Saaty, T. L. and Kainen, P. C. ``Line Graphs.'' §4-3 in The Four-Color Problem: Assaults and Conquest. New York: Dover, pp. 108-112, 1986.
- Undecagon
- Undecidable
- Undecillion
- Undetermined Coefficients Method
- Undulating Number
- Unduloid
- Unexpected Hanging Paradox
- Unfinished Game
- Unhappy Number
- Unicursal Circuit
- Uniform Apodization Function
- Uniform Boundedness Principle
- Uniform Convergence
- Uniform Distribution
- Uniform Polyhedron
- Uniform Variate
- Unimodal Distribution
- Unimodal Sequence
- Unimodular Group
- Unimodular Matrix
- Unimodular Transformation
- Union
- Uniplanar Double Point
- Unipotent
- Unique