Beyond trees: the metric geometry of subsets of weighted Hamming cubes

Abstract: Associated to any finite metric space are a large number of objects and quantities which provide some degree of structural or geometric information about the space. In this paper we show that in the setting of subsets of weighted Hamming cubes there are unexpected relationships between many of these quantities. We obtain in particular formulas for the determinant of the distance matrix, the $M$-constant and the cofactor sum for such spaces. In general, these types of results offer valuable insights into the combinatorial optimization of certain constrained quadratic forms on finite metric spaces. A key focus in this context are embedding properties of negative type metrics, which play a prominent role in addressing important questions like the sparsest cut problem in graph theory. The current work extends previous results for unweighted metric trees, and more generally, for subsets of standard Hamming cubes, as well as results for weighted metric trees. Finally we consider polygonal equalities in these spaces, giving a complete description of the nontrivial $1$-polygonal equalities that can arise in weighted Hamming cubes.