This function allows one to calculate the Fourier transform of a chirped function evaluated at specific points using the stationary phase approximation.
Imagine a pulse with a large time-bandwidth produce: this would require a large amount of data points in order to evaluate the Fourier transform. Lets imagine that you only needed to know the FT at specific points, or over a limited range, then clearly a DFT (FFT) would result in unwanted calculations and may not be possible due to memory constraints. Proper use of this function can result in a dramatic reduction in calculation time and memory requirements.
Adam Wyatt (2020). Stationary phase approximation for performing Fourier Transforms (https://www.mathworks.com/matlabcentral/fileexchange/20930-stationary-phase-approximation-for-performing-fourier-transforms), MATLAB Central File Exchange. Retrieved .