On the Number of Non-zero Elements of Joint Degree Vectors

Joint degree vectors give the number of edges between vertices of degree $i$ and degree $j$ for $1\le i\le j\le n-1$ in an $n$-vertex graph. We study the maximum number of nonzero elements in a joint degree vector of an $n$-vertex graph. This provides an upper bound on the number of estimable parameters on a bidegree-distribution based exponential random graph model.