This shader can be used to render materials with complex index of refraction. The regular VRayMtl material can compute the Fresnel effect for dielectric materials like plastic and glass based on the refractive index of the material; however metals have a more complicated Fresnel reflective curve that depends also on another parameter called extinction coefficient.
The shader is used as a reflection color map in a VRayMtl material with the VRayOSLTex texture, with the Fresnel option of the V-Ray material turned off (this shader does its own Fresnel calculations).
