Recursive Structure for DIT
The recursive structure of the binary FFT algorithm is a complete binary tree of logN levels shown below for N=16
At each phase, one relates the FFT of M numbers to FFT of even and odd subsets fE fO of this set -- these are of size M/2
Diagram shows binary digit (XXXX) of relevant elements
e.g. XXX1 are all odd indices m; XX11 is set 4m-+3 where m- lies between 0 and 3