Stationary phase approximation for performing Fourier Transforms

Performs a Fourier Transform of a function using the stationary phase approximation

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.