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Could somebody help me in writing mathematical expression for ARIMA (1,2,2)(1,0,0) with seasonal length of 7. I have got the coefficients as AR1: -0.0053, SAR7: -0.6610, MA1: 1.2858 and MA2:-0.3213. I have an expression but when forecasted manually, not matching with system generated one. Thanks,Pranesh

Pranesh
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    There have been some similar posts before, you could benefit from searching this site for ARIMA, SARIMA and other relevant keywords. – Richard Hardy Sep 22 '15 at 08:39
  • If you are having problems with the polynomials operations, you can check the examples in [this post](http://stats.stackexchange.com/questions/61510/how-do-i-write-a-mathematical-equation-for-arima-0-2-1-x-0-0-1-period-12/61527#61527) or [this other](http://stats.stackexchange.com/questions/150998/equivalence-of-regression-models-and-arima-models/151002#151002). See also other posts linked under the sections "Related" on the right-hand-side. – javlacalle Sep 22 '15 at 10:45
  • If you are having problems reproducing the forecast values from a software package, these posts may give you some helpful hints: [here](http://stats.stackexchange.com/questions/103010/) and [here](http://stats.stackexchange.com/questions/132635/arima-equation-interpretation). Check the definition of the ARIMA model that is used by your sofware package, in particular check the signs of the AR and MA coefficients; check also whether a constat is included as an intercept, $y_t = \alpha + \phi y_{t-1} + \epsilon_t$, or as a mean $(y_t - \mu) = \alpha + \phi(y_{t-1} - \mu) + \epsilon_t$. – javlacalle Sep 22 '15 at 10:46

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