Implementation of the Frequency Separation Technique in general lineshape codes

The Frequency Separation Technique (FST) has been proposed and theoretically documented. It is a technique capable of unifying and improving lineshape calculations, for both accuracy and speed. In this work, we briefly recall its key features and advantages and present a practical way of implementing it in lineshape codes. We note that the FST is a general technique, capable of working with practically any modern lineshape framework that can either employ or go beyond the standard framework.