s=tf('s');
wc=2.5/(0.8*s+1);
wd=c2d(wc,0.01,'tustin')
%b(1)=0.003322; b(2)=0.003322;
b=cell2mat(get(wd,'num'));
a=cell2mat(get(wd,'den'));

%a(1)=1; a(2)=-0.9934;
Ts=0.01;T=1000;
t=0 : Ts : T;
x1=randn(1,length(t)); 
x=0.01*x1;
y=filter(b,a,x);
R=xcorr(y);
tau=-15+Ts :Ts : 15;
lt=length(tau);
s1r=round(length(R)/2-lt/2);
s2r=round(length(R)/2+lt/2-1);
plot(tau,R(s1r:s2r)),grid

tau=[ 0 1 2 3 4 5 6 8 10 12 15];
%Rx=[0.3744  0.097  0.026  0.006  0.0025  0.0005  0.0003  0.0006  -0.0005 -0.0014 0];
%Rx=[0.031  0.017  0.0095  0.006  0.0025  0.0005  0.0003  0.0006  -0.0005  -0.0014 0];
%x=[-15 -12 -10 -6 -5 -4 -3 -2 -1 0 1 2 3 4 5 6 10 12 15];
%y=[0 -0.00014 -0.0005 0.0003 0.0005  0.0025  0.006 0.0095 0.017 0.031  0.017  0.0095  0.006  0.0025  0.0005  0.0003  0.0006  -0.0005  -0.0014];
%stem(x,y),grid;
%hold on
%plot(x,y)