Moving-average polynomial
= Moving-average polynomial
{title2=$\Theta(z)=1+\sum_{j=1}^q b_jz^j$}
The <moving-average polynomial> records the coefficients of the finite noise filter. Evaluating it at the <backshift operator> gives $\Theta(B)w_t=w_t+\sum_{j=1}^q b_jw_{t-j}$. In a reduced <ARMA> representation, invertibility is equivalent to having no roots in the closed unit disc.