y(t) = P1 y(t - 1) + P2 y(t - 2) + … + Pn y(t - n) + Q0 + a(t) - Q1 a(t - 1) - … - Qm a(t - m)
where:
y - time series at times t, t - 1, t - 2, ... , t - n
a - white noise with variance at times t, t - 1, t - 2, ... , t - m
n - order of autoregression
m - order of moving average
Q0 - overall constant
