On the magnitude of odd balls via potential functions

Abstract

Magnitude is a measure of size defined for certain classes of metric spaces; it arose from ideas in category theory. In particular, magnitude is defined for compact subsets of Euclidean space and, in arXiv:1507.02502, Barcel\'o and Carbery gave a procedure for calculating the magnitude of balls in odd dimensional Euclidean spaces. In this paper their approach is modified in various ways: this leads to an explicit determinantal formula for the magnitude of odd balls and leads to the conjecturing of a simpler formula in terms of Hankel determinants. This latter formula is proved using a rather different approach in arXiv:1708.03227, but the current paper provides the reasoning that lead to the formula being conjectured. Finally, an empirically-tested Hankel determinant formula for the derivative of the magnitude is conjectured.