The chord-length distribution of a polyhedron

Acta Crystallogr A Found Adv. 2020 Jul 1;76(Pt 4):474-488. doi: 10.1107/S2053273320004519. Epub 2020 Jun 1.

Abstract

The chord-length distribution function [γ''(r)] of any bounded polyhedron has a closed analytic expression which changes in the different subdomains of the r range. In each of these, the γ''(r) expression only involves, as transcendental contributions, inverse trigonometric functions of argument equal to R[r, Δ1], Δ1 being the square root of a second-degree r polynomial and R[x, y] a rational function. As r approaches δ, one of the two end points of an r subdomain, the derivative of γ''(r) can only show singularities of the forms |r - δ|-n and |r - δ|-m+1/2, with n and m appropriate positive integers. Finally, the explicit analytic expressions of the primitives are also reported.

Keywords: asymptotic behaviour; chord-length distribution; integral geometry; polyhedra; small-angle scattering; stochastic geometry.