Re: [R] question about xreg of arima

Thanks Richard. I am just trying to understand exactly what is R's arima doing, and I am having a hard time. It seems that xreg is necessary to force arima to include the constant term, but it appears that exactly how this is done is not documented. If a series is not differenced, e.g. AR(1), then

Re: [R] question about xreg of arima

Tom A constant term is not included in the model if any differencing is specified. The xreg= parameter is used to add other explanatory variables to the model. In your case xreg=1:length(x) adds a vector of 1's to the model. Robert Shumway and David Stoffer's website for their "Time Series Analys

[R] question about xreg of arima

Hi, I am trying to understand exactly what xreg does in arima. The documentation for xreg says:"xreg Optionally, a vector or matrix of external regressors, which must have the same number of rows as x." What does this mean with regard to the action of xreg in arima? Apparently somehow xreg made t