On Optimal Beyond-Planar Graphs

01/03/2022

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by   Franz J. Brandenburg, et al.

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A graph is beyond-planar if it can be drawn in the plane with a specific restriction on crossings. Several types of beyond-planar graphs have been investigated, such as k-planar if every edge is crossed at most k times and RAC if edges can cross only at a right angle in a straight-line drawing. A graph is optimal if the number of edges coincides with the density for its type. Optimal graphs are special and are known only for some types of beyond-planar graphs, including 1-planar, 2-planar, and RAC graphs. For all types of beyond-planar graphs for which optimal graphs are known, we compute the range for optimal graphs, establish combinatorial properties, and show that every graph is a topological minor of an optimal graph. Note that the minor property is well-known for general beyond-planar graphs.