Paper
Improved upper bounds on Zarankiewicz numbers
Authors
Sara Davies, Peter Gill, Daniel Horsley
Abstract
For positive integers and , the Zarankiewicz number is the maximum number of edges in a subgraph of that has no complete bipartite subgraph containing vertices in the part of size and vertices in the part of size . The best general upper bound on Zarankiewicz numbers is a bound due to Roman that can be viewed as the optimal value of a simple linear program. Here we show that in many cases this bound can be improved by adding additional constraints to this linear program. This allows us to prove new upper bounds on Zarankiewicz numbers for many small parameter sets. We are also able to establish a new family of closed form upper bounds on that captures much, but not all, of the power of the new constraints. This bound generalises a recent result of Chen, Horsley and Mammoliti that applied only in the case .