I have been reading ARMA MODELS AND THE BOX JENKINS METHODOLOGY by S. MAKRIDAKIS AND M. HISON 95/45/TM .
I seem to be just a little stuck on the idea of using "trends". I think of a "trend" as a $y$ intercept and a slope. They state in eq. 4, that $$T_t = a + bt$$ So, I get $a$ is the $y$ intercept and $b$ is the slope. When they then say:
$$T'(t,L)= S_t + \sum_{i=1}^L \phi^i T' _{t-L}$$
Neglecting $S$, does this mean then:
$$a'(T,L)= \sum_{i=1}^L \phi^i a'_{t-L}$$
and
$$b'(T,L)=\sum_{i=1}^L \phi^i b'_{t-L}$$
?? is that all?