spec.ar {stats}  R Documentation 
Fits an AR model to x
(or uses the existing fit) and computes
(and by default plots) the spectral density of the fitted model.
spec.ar(x, n.freq, order = NULL, plot = TRUE, na.action = na.fail, method = "yulewalker", ...)
x 
A univariate (not yet:or multivariate) time series or the
result of a fit by 
n.freq 
The number of points at which to plot. 
order 
The order of the AR model to be fitted. If omitted, the order is chosen by AIC. 
plot 
Plot the periodogram? 
na.action 

method 

... 
Graphical arguments passed to 
An object of class "spec"
.
The result is returned invisibly if plot
is true.
Some authors, for example Thomson (1990), warn strongly that AR spectra can be misleading.
The multivariate case is not yet implemented.
Thompson, D.J. (1990) Time series analysis of Holocene climate data. Phil. Trans. Roy. Soc. A 330, 601–616.
Venables, W.N. and Ripley, B.D. (2002) Modern Applied Statistics with S. Fourth edition. Springer. (Especially page 402.)
require(graphics) spec.ar(lh) spec.ar(ldeaths) spec.ar(ldeaths, method = "burg") spec.ar(log(lynx)) spec.ar(log(lynx), method = "burg", add = TRUE, col = "purple") spec.ar(log(lynx), method = "mle", add = TRUE, col = "forest green") spec.ar(log(lynx), method = "ols", add = TRUE, col = "blue")