The Lovász number of random circulant graphs

Afonso S Bandeira, Jaroslaw Blasiok, Daniil Dmitriev, Ulysse Faure, Anastasia Kireeva, Dmitriy Kunisky

Session: General

Keywords: Semidefinite programming, random graphs, restricted isometry property

TL;DR: We provide upper and lower bounds for expected value of the Lovász number of a random circulant graph, which are tight up to log log factor.

Abstract:

This paper addresses the behavior of the Lovász number for dense random circulant graphs.
The Lovász number is a well-known semidefinite programming upper bound on the independence number.
Circulant graphs, an example of a Cayley graph, are highly structured vertex-transitive graphs on integers modulo n, where the connectivity of pairs of vertices depends only on the difference between their labels.
While for random circulant graphs the asymptotics of fundamental quantities such as the clique and the chromatic number are well-understood, characterizing the exact behavior of the Lovász number remains open.
In this work, we provide upper and lower bounds on the expected value of the Lovász number and show that it scales as the square root of the number of vertices, up to log log factor.
Our proof reduces the semidefinite program formulation of the Lovász number to a linear program with random objective and constraints via diagonalization of the adjacency matrix of a circulant graph by the discrete Fourier transform (DFT).
This leads to a problem about controlling the norms of vectors with sparse Fourier coefficients, which we study using results on the restricted isometry property of subsampled DFT matrices.

Submission Number: 85