On a Conjecture of Nagy on Extremal Densities

Abstract

We disprove a conjecture of Nagy on the maximum number of copies N(G,H) of a fixed graph G in a large graph H with prescribed edge density. Nagy conjectured that for all G, the quantity N(G,H) is asymptotically maximised by either a quasi-star or a quasi-clique. We show this is false for infinitely many graphs, the smallest of which has 6 vertices and 6 edges. We also propose some new conjectures for the behaviour of N(G,H), and present some evidence for them.