250. AR

Autoregressive

i.e.,

Stationary if all roots of lie outside the unit circle

Parameters: , ,
Orders:

Example:

Given

  • Order:
  • Parameters: ,
  • Data:
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
12 10 8 11 14 12 9 13 16 14 11 15 18 16 13 17

Step 1 — formula

Substitute into the AR recursion:

Forecast (set ):

Innovation:

Step 2 — apply at

Plug in , , and :

Step 3 — iterate

2 10
3 8
4 11
5 14
6 12
7 9
8 13
9 16
10 14
11 11
12 15
13 18
14 16
15 13
16 17
17

Residuals are large because AR(1) cannot capture the trend or seasonality in — that is the role of ARIMA / SARIMA / ETS, applied to the same data in their own examples.