Hello, Guys: I'm from China, my English is poor and I'm new to R. This is my first time to use R-help. Hope that I can get useful suggestions from you warm-hearted guys. Thanks. I builded a multiplicative seasonal ARMA model to a series named "cDownRange". And the order is (1,1)*(0,1)45 I fitted the model in R and get the result as below: Call:arima(x = cDownRange, order = c(1, 0, 1), seasonal = list(order = c(0, 1, 1), period = 45))Coefficients: ar1 ma1 sma1 0.7364 -0.5046 -0.9511s.e. 0.0458 0.0594 0.0130When I use the predict command of this model in R, it gives the right forcasting. So I think the forcast formula of this SARMA model should be written as below:X(t)=ar1*X(t-1)-ma1*a(t-1)-sma1*a(t-45)+ma1*sma1*a(t-46)But when I use this forcast formula in Excel, it gives a totally different predict from R. And I don't know why? I guess the expression of the forcast formula of this SARMA(1,1)*(0,1)45 is wrong, but I don't know the right form. Can anybody help me with this?Thank, again! saji from Shanghai _________________________________________________________________ [[elided Hotmail spam]] [[alternative HTML version deleted]]