what is the purpose of this xreg argument in arima when using arima model how is xreg used why use xreg in arima what is the xreg argument in arima r used for what is use xreg how to use exreg r model what is the purpose of ARIMA model what is the argument for xreg in arcima what is the purpose of xreg for arima? what is the purpose of xreg in r when does arima use exreg arima - xreg argument why use xreg argument in arima what is the purpose of using xreg in arima what is the purpose of the xreg argument in arima? when r use xreg argument what is the x-reg argument in arima what is the purpose of xreg in r arima definition r what is xreg argument