On the Graph Complement Conjecture for Minimum

The minimum rank of a graph has been an interesting and well studied parameter 6 investigated by many researchers over the past decade or so. One of the many unresolved questions on 7 this topic is the so-called graph complement conjecture, which grew out of a workshop in 2006. This 8 conjecture asks for an upper bound on the sum of the minimum rank of a graph and the minimum rank 9 of its complement, and may be classified as a Nordhaus-Gaddum type problem involving the graph 10 parameter minimum rank. The conjectured bound is the order of the graph plus two. Other variants 11 of the graph complement conjecture are introduced here for the minimum semidefinite rank and the 12 Colin de Verdière type parameter ν. We show that if the ν-graph complement conjecture is true for 13 two graphs then it is true for the join of these graphs. Related results for the graph complement 14 conjecture (and the positive semidefinite version) for joins of graphs are also established. We also 15 report on the use of recent results on partial k-trees to establish the graph complement conjecture 16 for graphs of low minimum rank. 17