echo on
p=2; q=2; n=500;
sigma2=2.25; sigma=sqrt(sigma2);
PHI = [0.5,0.2]; THETA = -[0.5,0.2]; 
[x,phir,thetar]=armagen(PHI,THETA,n,sigma);
phir, thetar
[xro,xroE,mi,miE,xacf]=acf(x,figure);
[xpacf,phi,phiE,v]=pacf(xacf(1:p+1),n,figure);
v
xs=conv(x,[0;phi]); xs=xs(1:n);
length(xs)
% figure; plot(1:n,x,'w',1:n,xs,'y--');
ve=std(xs-x).^2
echo off