N-beam interactions examined with the help of the computer programs PSIINT and PSILAM

Two computer programs – one for calculation and graphical representation of the azimuthal angle ψ of all possible multiple reflections versus the wavelength λ (PSILAM) and one for the simulation of the Umweganregung-intensity variation during rotation of the crystal about the scattering vector of a `forbidden' or very weak reflection (PSIINT) – have been developed on the basis of the program UMWEG [Rossmanith (1985). Z. Kristallogr. 171, 253–254; (1986). Acta Cryst. A42, 344–348] with emphasis on suitability for inexpensive hardware. Examples of the excellent agreement between measurements and calculations and of the necessity of the combined application of both programs are given.