dft(h, N)

Function to calculate the DFT of a signal in the time domain (given in its discrete samples)
%DFT compute the Discrete Fourier Transform of N samples
% calling: [H,W] = dft (h, N)
% h: input vector of finite length, L
% N:frequency bandwidth on (-pi, pi) with condition: N >= L
% W:DFT bandwidth
% H: Frequency response