恰逢清明，这几天是清明时节雪纷纷，断崖式降温；又回到了老家，儿时上蹿下跳的核桃树，远去的故乡，远去的时代……
用到的公式：
这里只放前两个小题的计算过程，都比较简单，细心就行。代码如下：
%% ------------------------------------------------------------------------
%% Output Info about this m-file
fprintf('\n***********************************************************\n');
fprintf(' <DSP using MATLAB> Problem 5.1 \n\n'); banner();
%% ------------------------------------------------------------------------ % ------------------------------------
% x1(n)
% ------------------------------------
xn = [4, 1, -1, 1]; N =4;
Xk_1 = dfs(xn,N) % ------------------------------------
% x2(n)
% ------------------------------------
xn = [2, 0, 0, 0, -1, 0, 0, 0]; N = 8;
Xk_2 = dfs(xn,N) % ------------------------------------
% x3(n)
% ------------------------------------
xn = [1, 0, -1, -1, 0]; N = 5;
Xk_3 = dfs(xn,N) % ------------------------------------
% x4(n)
% ------------------------------------
xn = [0, 0, 2*j, 0, 2*j, 0]; N = 6;
Xk_4 = dfs(xn,N) % ------------------------------------
% x5(n)
% ------------------------------------
xn = [3, 2, 1]; N = 3;
Xk_5 = dfs(xn,N)
运行结果：
