N=16; 
xn=[ones(1,N/4),zeros(1,3*N/4)];
xn=[xn,xn,xn];
n=0:3*N-1;
k=0:3*N-1;
Xk=xn*exp(-j*2*pi/N).^(n'*k);   %離散傅里葉級數變換
x=Xk*exp(j*2*pi/N).^(n'*k)/(3*3*N); %離散傅里葉級數逆變換
subplot(2,2,1),stem(n,xn,'k');
title('x(n)');axis([-1,3*N,1.1*min(xn),1.1*max(xn)]);
subplot(2,2,2),stem(n,abs(x),'k');%顯示逆變換結果
title('IDFS|X(k)|');
axis([-1,3*N,1.1*min(x),1.1*max(x)]);
subplot(2,2,3),stem(k,abs(Xk),'k');%顯示序列的幅度譜
title('|X(k)|');
axis([-1,3*N,1.1*min(abs(Xk)),1.1*max(abs(Xk))]);
subplot(2,2,4),stem(k,angle(Xk),'k');%顯示序列的相位譜
title('arg|X(k)|');
axis([-1,3*N,1.1*min(angle(Xk)),1.1*max(angle(Xk))]);