n=0:31;
x=cos(3/8*pi*n);
y=fft(x,32);
subplot(2,1,1); 
stem(n,y);
xlabel('頻譜分析');
y2=[zeros(1,6),16,zeros(1,19),16,zeros(1,5)];
subplot(2,1,2);
error=y-y2;
stem(n,error);
xlabel('誤差');