Do I need to differentiate ARIMA model input data?
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If my ARIMA model is (1,1,1), do I need to differentiate the data before inserting it into the model?
sys = arima(1,1,1);
Md1 = estimate(sys,data); % Model 1
Md2 = estimate(sys,diff(data)); % Model 2
Which option is correct, Model 1 or Model 2?