I got an idea how and why dft works from prof.Wilf(RIP) http://www.math.upenn.edu/~wilf/AlgoComp.pdf http://www.math.upenn.edu/~wilf/AlgoComp.pdf see from page

I got an idea how and why dft works from prof.Wilf(RIP) http://www.math.upenn.edu/~wilf/AlgoComp.pdf http://www.math.upenn.edu/~wilf/AlgoComp.pdf see from page 50 on. He approaches it from the algebraical side