Metric geodesic covers of graphs

TL;DR

This paper investigates the minimal covers of graphs by geodesics under various metrics, providing computational methods to determine these covers for standard graphs and classifying spaces with a cover number of three.

Contribution

It introduces reductions for computing optimal geodesic covers of graphs and classifies topological spaces with a cover number of three, linking them to planarity.

Findings

Computed geodesic cover numbers for $K_4$, $K_5$, and $K_{3,3}$.

Provided a catalogue of spaces with cover number 3.

Proved that spaces with cover number 3 are planar.

Abstract

We study the problem of finding, for a given one-dimensional topological space $X$, a cover of $X$ of smallest size by geodesics with respect to some metric. The infimal size of such a set is called the metric geodesic cover number of $X$. We prove reductions enabling us to find, with computer assistance, optimal geodesic covers of a graph and use these to determine the cover number of several standard graphs, including $K_4$, $K_5$ and $K_{3,3}$. We also give a catalogue of topological spaces with cover number $3$, and use it to deduce that any such space must be planar.