Edge crossings in random linear arrangements

TL;DR

This paper analyzes the distribution of edge crossings in random linear arrangements of various network types, providing formulas for expectation and variance, and exploring their asymptotic scaling.

Contribution

It generalizes the expectation formula for edge crossings from trees to arbitrary networks and derives a novel variance expression applicable to any layout.

Findings

Derived formulas for expectation and variance of crossings in various network classes.

Found asymptotic power-law scaling of crossings with network size.

Extended analysis to complete, bipartite, cycle, and special tree graphs.

Abstract

In spatial networks vertices are arranged in some space and edges may cross. When arranging vertices in a 1-dimensional lattice edges may cross when drawn above the vertex sequence as it happens in linguistic and biological networks. Here we investigate the general of problem of the distribution of edge crossings in random arrangements of the vertices. We generalize the existing formula for the expectation of this number in random linear arrangements of trees to any network and derive an expression for the variance of the number of crossings in an arbitrary layout relying on a novel characterization of the algebraic structure of that variance in an arbitrary space. We provide compact formulae for the expectation and the variance in complete graphs, complete bipartite graphs, cycle graphs, one-regular graphs and various kinds of trees (star trees, quasi-star trees and linear trees). In these networks, the scaling of expectation and variance as a function of network size is asymptotically power-law-like in random linear arrangements. Our work paves the way for further research and applications in 1-dimension or investigating the distribution of the number of crossings in lattices of higher dimension or other embeddings.