xn1=[1,1,0,0,0,0,0,0,0,0];
N=length(xn1);
xn=[xn1,xn1,xn1,xn1];
n=0:4*N-1;
k=0:4*N-1;
Xk=xn*exp(-j*2*pi/N).^(n'*k);       %離散傅里葉級數(shù)變換
subplot(2,2,1),stem(xn1,'k');
title('x(n)');axis([0,N,1.1*min(xn),1.1*max(xn)]);
subplot(2,2,2),stem(n,xn,'k');%顯示逆變換結(jié)果
title('x(n+4r)');
axis([-1,4*N,1.1*min(xn),1.1*max(xn)]);
subplot(2,2,3),stem(k,abs(Xk),'k');%顯示序列的幅度譜
title('|X(k)|');
axis([-1,4*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([-1,4*N,1.1*min(angle(Xk)),1.1*max(angle(Xk))]);