I have an auto.arima model output with ARIMA(000)(110) with sigma^2=0.005, so I assume the model fits well the data. But I'm trying to understand the model itself... If I did all the maths correctly, the change at time t depends on the change at the same time in 2 previous years, being expressed as:
xt = (α1+1) xt-4 - α1xt-8 + wt.
Is it correct?