终于看到第5章了，继续努力，加油！！！
代码：
xn = [0, 1, 2, 3]; N =4;
Xk = dfs(xn,N)
用到的dfs函数：
function [Xk] = dfs(xn,N)
%% Computes Discrete Fourier Series Coefficients
%% ---------------------------------------------
%% [Xk] = dfs(xn,N)
%% Xk = DFS coeff. array over 0 <= k <= N-1
%% xn = One period of periodic signal over 0 <=n <= N-1
%% N = Fundamental period of xn
%%
n = [0:1:N-1]; % row vector for n
k = [0:1:N-1]; % row vector for k
WN = exp(-j*2*pi/N); % Wn factor
nk = n'*k; % creates a N by N matrix of nk values
WNnk = WN .^ nk; % DFS matrix
Xk = xn * WNnk; % row vector for DFS coefficients
运行结果：
