X = arf(X,A,Z,Range,...)
X [ tseries ] - Input data from which initial condition will be taken.
A [ numeric ] - Vector of coefficients of the autoregressive polynomial.
Z [ numeric | tseries ] - Exogenous input series or constant in the autoregressive process.
Range [ numeric | Inf ] - Date range on which the new time series observations will be computed; RANGE does not include pre-sample initial condition. Inf means the entire possible range will be used (taking into account the length of pre-sample initial condition needed).
X [ tseries ] - Output data with new observations created by running an autoregressive process described by A and Z.The autoregressive process has one of the following forms:
A1*x + A2*x(-1) + ... + An*x(-n) = z,
or
A1*x + A2*x(+1) + ... + An*x(+n) = z,
depending on whether the range is increasing (running forward in time), or decreasing (running backward in time). The coefficients A1,...An are gathered in the input vector A,
A = [A1,A2,...,An].
The following two lines create an autoregressive process constructed from normally distributed residuals,
$$ x_t = \rho x_{t-1} + \epsilon_t $$
rho = 0.8;
X = tseries(1:20,@randn);
X = arf(X,[1,-rho],X,2:20);