%Z變換解差分方程
b=2*[1,2,3];
a=[1,-0.8,0.4];
Y=[-2,-3];
X=[1,1];
xx=filter(b,a,Y,X);
bxplus=[1 -0.5];
axplus=[1,-1];
ayplus=conv(a,axplus);
byplus=conv(b,bxplus)+conv(xx,axplus);
[R,P,C]=residuez(byplus,ayplus)
M=abs(p)
A=angle(P)/pi
n=0:50;
x=cos(pi*n/3);
y=filter(b,a,x,xx);
plot(n,y);