function acf = armaacf(phi,theta,n)
% ARMA_ACF(PHI,THETA,N) computes acf out to lag N of ARMA model with
%   given coefficients in (PHI,THETA).
% phi, theta must be column vectors (px1 and qx1, respectively).
acvf = armaacvf(phi,theta,n);
acf = acvf/acvf(1);