Look at the R help files for predict.Arima rather than using forecast to forecast an ARIMA model. You might plot your data and the first difference and you should be able to come to a conclusion about stationarity. With your very small data set you need a very parsimonious model. Knowledge about the nature of the data set would also be important. I see no seasonal effect in the data and wonder why you are proposing to allow two seasonal differences. Probably some form of smoothing would be more suitable in your case.
Best Regards John On 29/11/2007, Ozcan Asilkan <[EMAIL PROTECTED]> wrote: > Hi ohn, > > Thank you for your reply. I read in a few documents that if a Time Series > data is NONStationary, ARIMA models must be used. So, if we suppose that my > data is non-stationary, is it basically enough just to use the arima() > function in R to make a future forecast ? Does arima function implicitly > convert my data into stationary status by handling differencing, removing > seasonality, etc. ? Or must I explicitly convert my data to stationary form > in order to use arima() ? > > and here' s my code. I' ll appreciate your help making suggestions.. Thank > you very much. > > Best regards.. > Ozzy > > # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # > # Loading the library... > library(forecast) > > # my input data having 3 years of monthly data (36 data) > invec <- > c(15289,14282,16153,15885,15369,15488,15462,14697,15512,15506,15271,15111,14963,15150,15061,14896,15147,14967,15026,15102,14880,15181,14979,15300,15377,15323,15462,15422,15598,15518,15497,15593,15348,15453,15361,15361) > > # converting to TS > invecTS <- ts(invec, start = c(2005,1), frequency = 12) > > # using arima function > invecTSAR = arima(invecTS, order = c(0,1,1), seasonal = list(order = c(0, 2, > 0) ) ) > > # making a further 2 years forecasting (=24 months) > invecTSARPR <- forecast(invecTSAR,24) > > # and plotting > plot(invecTSARPR,xlab="TIME", ylab="PRICE (€)", fcol="red",plot.conf=F) > > # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # > > > On Nov 26, 2007 10:30 PM, Uwe Ligges > <[EMAIL PROTECTED]> wrote: > > > > > > > > Ozcan Asilkan wrote: > > > Hello, > > > > > -- John C Frain Trinity College Dublin Dublin 2 Ireland www.tcd.ie/Economics/staff/frainj/home.html mailto:[EMAIL PROTECTED] mailto:[EMAIL PROTECTED] ______________________________________________ R-help@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.
