[Specification] Elliptical footprint approximation

From the Vulkan (1.0.62) specification (15.6.7 Scale Factor Operation, Level-of-Detail Operation and Image Level(s) Selection):

The scale factors ρx and ρy, calculated from the magnitude of the derivatives in x and y, are used to compute the minimum and maximum scale factors.

This isn't correct; you cannot determine the maximum and minimum scale factors with just these scale factors.

ρx and ρy may be approximated with functions fx and fy

This should probably read

ρmin and ρmax may be approximated with functions fx and fy

with the following subsequent alteration:

The minimum and maximum scale factors (ρmin,ρmax) are given, under this approximation, by
ρmax = max(fx, fy)
ρmin = min(fx, fy)