Chirp Z-transform
This is an implementation of the Chirp Z-transform in pure Kotlin. It works via FFT convolution.
The Chirp Z-transform computes
X[k] = sum_{n=0}^{N-1} x[n] u^(-n) w^(nk) (k = 0,...,M-1)
for a complex number u and w. The effect is to evaluate the Z-transform:
X(z) = sum_{n=0}^{N-1} x[n] z^(-n)
along a logarithmic spiral in the complex plane.
One major use of the Chirp Z-transform is to evaluate a subinterval of frequencies with higher frequency resolution for the same number of inputs as an FFT.