%y(n)=x(n)+0.7x(n-1)-0.8y(n-1)+0.25(n-2)
%y(n)+0.8y(n-1)-0.25y(n-2)=x(n)+0.7x(n-1);
clear;
num = [1 0.7 0];
den = [1 0.8 -0.25];
figure(1);
impz(num,den); %冲击响应
figure(2);
freqz(num,den);% 系统频率响应
G=tf(num,den,-1);
disp('系统传递函数H(z)');
printsys(num,den,'z');
%画出零极点图
figure(3);
zplane(num,den)
t=0:1:100;
x = 2*(0.9).^t; %激励源
y1=lsim(G,x,t); %求出系统全响应
figure(4);
subplot(211),plot(t,x);
title('激励信号');
subplot(212),plot(t,y1);
title('系统响应');