Some functions for Origin 7.0 for reflectivity calculations:

FRESNEL.CPP - fresnel reflectivity

RHO.CPP - density models
There are currently two models incorporated: Distored Crystal Model and two layers on a substrate

BORRATT.CPP - includes both born and parratt calculations
Uses rho.cpp file calling rho() function with up to 8 paramaters, which you can use
to define your custom density function