(k,p)-Planarity: A Relaxation of Hybrid Planarity

TL;DR

This paper introduces a new graph planarity model called (k,p)-planarity, explores its properties, and proves that certain planarity testing problems within this model are NP-complete, revealing a large and distinct class of graphs.

Contribution

The paper defines the (k,p)-planarity model, bounds edge counts, and establishes NP-completeness for specific planarity testing problems, highlighting its novelty and complexity.

Findings

Bound the number of edges in (k,p)-planar graphs for p<k

NP-completeness of (4,1)-planarity testing

NP-completeness of (2,2)-planarity testing

Abstract

We present a new model for hybrid planarity that relaxes existing hybrid representations. A graph $G = (V,E)$ is $(k,p)$-planar if $V$ can be partitioned into clusters of size at most $k$ such that $G$ admits a drawing where: (i) each cluster is associated with a closed, bounded planar region, called a cluster region; (ii) cluster regions are pairwise disjoint, (iii) each vertex $v \in V$ is identified with at most $p$ distinct points, called \emph{ports}, on the boundary of its cluster region; (iv) each inter-cluster edge $(u,v) \in E$ is identified with a Jordan arc connecting a port of $u$ to a port of $v$; (v) inter-cluster edges do not cross or intersect cluster regions except at their endpoints. We first tightly bound the number of edges in a $(k,p)$-planar graph with $p<k$. We then prove that $(4,1)$-planarity testing and $(2,2)$-planarity testing are NP-complete problems. Finally, we prove that neither the class of $(2,2)$-planar graphs nor the class of $1$-planar graphs contains the other, indicating that the $(k,p)$-planar graphs are a large and novel class.