scgmlz/BornAgain: Release 1.18.0

The most important change is improved numerics for the computation of reflection and transmission of scalar or polarized beams. The new algorithms is numerically stable even for arbitrarily many layers and for low overall transmission. For rough interfaces, one can choose between a tanh scattering-length density profile and the Névot-Croce approximation. There is a new documentation section with polarized reflectometry examples.

There are a few API changes. Some classes have been renamed for clarity or brevity:

• FootprintSquare, FootprintGauss, FormFactorHollowSphere, CosineRipple, SawtoothRipple.
• FormFactorGaussSphere now models a sphere, not an ellipsoid.
• FormFactorSphereLogNormalRadius is now positioned at the center, not at the bottom.
• In constructors that involve the Voigt function, the order of the arguments gamma and eta has been unified.

In examples, the material with refractive index 1 has been renamed from "air" to "vacuum".