Usually I try to post questions when I've already managed to accomplish something with the problem but this time I'm really at a lost in here.
The problem goes something like this (sorry for any mistranslation) : Consider the discrete Fourier transform, obtain the $\mathbf{F_8}$ and $\mathbf{F_1}_6$, then factorize the matrices to apply the Fast Fourier Transform and finally verify the equivalence of the transforms. Consider $2l=2\pi$ and $N=8$, $N=16$.
I have an idea on how to obtain $\mathbf{F_8}$ and $\mathbf{F_1}_6$ but have no idea on what to do next.
Any help would be greatly appreciated, this is just sort of a bonus exercise but still would like to know how to solve it.