Nonisotropic Rayleigh–Ritz discriminants for rank-one matrices

A logarithmic compactification of the critical-point correspondence on
$\mathbb{P}^{m-1} \times \mathbb{P}^{n-1}$ gives a coefficient formula for its
nonisotropic Rayleigh–Ritz discriminant. Its derivation counts ramification on
a general parameter pencil, computes the boundary contributions by first-jet
bundles, and gives an argument that the nonisotropic ramification maps
generically one-to-one onto a reduced irreducible hypersurface. The formula
yields $24\binom{n+1}{3}$ for $m = 2$ and $24n^2\binom{n}{2}$ for $m = 3$, for
every $n \ge 2$, as conjectured by Borovik, Friedman, Hoşten and Pfeffer. The
degree calculation includes the isotropic boundary and its crossings.