Journal of Graph Algorithms and Applications

Special Issue on Selected Papers from the 14th International Conference and Workshops on Algorithms and Computation, WALCOM 2020

DOI: 10.7155/jgaa.00576

Angle Covers: Algorithms and Complexity

William Evans, Ellen Gethner, Jack Spalding-Jamieson, and Alexander Wolff

Vol. 25, no. 2, pp. 643-661, 2021. Regular paper.

Abstract Consider a graph with a rotation system, namely, for every vertex, a circular ordering of the incident edges. Given such a graph, an angle cover maps every vertex to a pair of consecutive edges in the ordering- an angle- such that each edge participates in at least one such pair. We show that any graph of maximum degree 4 admits an angle cover, give a poly-time algorithm for deciding if a graph without a degree-3 vertex has an angle cover, and prove that, given a graph of maximum degree 5, it is NP-hard to decide whether it admits an angle cover. We also consider extensions of the angle cover problem where every vertex selects a fixed number $a>1$ of angles or where an angle consists of more than two consecutive edges. We show an application of angle covers to the problem of deciding if the 2-blowup of a planar graph has isomorphic thickness 2.