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arXiv · 1309.1046

Saturated simple and $k$-simple topological graphs

Jan Kynčl·János Pach·Radoš Radoičić·Géza Tóth
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Abstract

A simple topological graph $G$ is a graph drawn in the plane so that any pair of edges have at most one point in common, which is either an endpoint or a proper crossing. $G$ is called saturated if no further edge can be added without violating this condition. We construct saturated simple topological graphs with $n$ vertices and $O(n)$ edges. For every $k>1$, we give similar constructions for $k$-simple topological graphs, that is, for graphs drawn in the plane so that any two edges have at most $k$ points in common. We show that in any $k$-simple topological graph, any two independent vertices can be connected by a curve that crosses each of the original edges at most $2k$ times. Another construction shows that the bound $2k$ cannot be improved. Several other related problems are also considered.

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Jan Kynčl, János Pach, Radoš Radoičić, Géza Tóth. 2014-05-30. Saturated simple and $k$-simple topological graphs. https://doi.org/10.1016/j.comgeo.2014.10.008

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