xn=[0,1,2,3,4,5,6,7];
N=length(xn);
n=0:N-1;
w=linspace(-2*pi,2*pi,500);%將[-2π,2π]區(qū)間分割為500份
X=xn*exp(-j*n'*w);            %離散時間傅里葉變換
subplot(3,1,1),stem(n,xn,'k');
ylabel('x(n)');
subplot(3,1,2),plot(w,abs(X),'k');  %顯示序列的幅度譜
axis([-2*pi,2*pi,1.1*min(abs(X)),1.1*max(abs(X))]);
ylabel('幅度譜');
subplot(3,1,3),plot(w,angle(X),'k');%顯示序列的相位譜
axis([-2*pi,2*pi,1.1*min(angle(X)),1.1*max(angle(X))]);
ylabel('相位譜');