ms13_1.m

《数字信号处理实验(MATLAB版)》这

xn1=[0,1,2,4];       %建立xn1序列
xn2=[1,0,1,0,1];     %建立xn2序列
N1=length(xn1);N2=length(xn2);
N=max(N1,N2);        %确定N
if N1>N2 xn2=[xn2,zeros(1,N1-N2)]; %对长度短的序列补0 
elseif N2>N1 xn1=[xn1,zeros(1,N2-N1)];
end
yn=2*xn1+3*xn2;      %计算yn
n=0:N-1;k=0:N-1;
Yk1=yn*(exp(-j*2*pi/N)).^(n'*k) %求yn的N点DFT
Xk1=xn1*(exp(-j*2*pi/N)).^(n'*k);%求xn1的N点DFT
Xk2=xn2*(exp(-j*2*pi/N)).^(n'*k);%求xn2的N点DFT
Yk2=2*Xk1+3*Xk2     %由Xk1、Xk2求Yk
figure(1);
subplot(4,1,1),stem(n,xn1,'k');ylabel('x1(n)'); 
axis([-1,N,0,1.1*max(xn1)]);
subplot(4,1,2),stem(n,xn2,'k');ylabel('x2(n)');
axis([-1,N,0,1.1*max(xn2)]);
subplot(4,1,3),stem(n,yn,'k');ylabel('y(n)'); 
axis([-1,N,0,1.1*max(yn)]);
subplot(4,1,4),stem(n,abs(Yk1),'k');ylabel('DFT[y(n)]'); 
axis([-1,N,0,1.1*max(abs(Yk1))]);
figure(2);
subplot(3,1,1),stem(n,abs(Xk1),'k');ylabel('X1(k)');  
axis([-1,N,0,1.1*max(abs(Xk1))]);
subplot(3,1,2),stem(n,abs(Xk2),'k');ylabel('X2(k)'); 
axis([-1,N,0,1.1*max(abs(Xk2))]);
subplot(3,1,3),stem(n,abs(Yk2),'k');ylabel('2*X1(k)+3*X2(k)'); 
axis([-1,N,0,1.1*max(abs(Yk2))]);