i have tried replicating the SAS ARIMA (AR model) model in excel and have been successful for the most part... below is the equation that i am using.. below is the equation for p =(1,7,14) model with no d and q terms Yt = Constant Estimate + ar1*lag1 +ar7*lag7 +ar14*lag14 if the model has other input variables apart from these 3 lags, below is the equation (p =(1,7,14), with input=Temp, with no d and q terms): Yt = Constant Estimate + ar1*lag1 +ar7*lag7 +ar14*lag14+ num1*Temp-ar1*num1*temp1-ar7*num1*temp7-ar14*num1*temp14 hope this helps. thanks

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