
$${b}_{t}={\delta}_{1}{b}_{t1}+{\delta}_{2}{b}_{t2}+\cdots +{\delta}_{p}{b}_{tp}+{\omega}_{0}{y}_{tb}{\omega}_{1}{y}_{tb1}\cdots {\omega}_{q}{y}_{tbq}\text{.}$$  (1) 
(i)  The equation (1) is applied from $t=1+b+q,\dots ,n$ so all terms in ${y}_{t}$ on the righthand side of (1) are known, the unknown set of values ${b}_{t}$ for $t=b+q,\dots ,b+q+1p$ being taken as zero. 
(ii)  The unknown values of ${y}_{t}$ for $t\le 0$ are estimated by backforecasting exactly as for G13BAF. 
On entry,  ${\mathbf{NMR}}\ne 3$ and ${\mathbf{NMR}}\ne 10$, 
or  ${\mathbf{MR}}\left(\mathit{i}\right)<0$, for $\mathit{i}=1,2,\dots ,{\mathbf{NMR}}$, 
or  ${\mathbf{NMR}}=10$ and ${\mathbf{MR}}\left(10\right)=1$, 
or  ${\mathbf{NMR}}=10$ and ${\mathbf{MR}}\left(10\right)=0$ and ${\mathbf{MR}}\left(7\right)+{\mathbf{MR}}\left(8\right)+{\mathbf{MR}}\left(9\right)\ne 0$, 
or  ${\mathbf{NMR}}=10$ and ${\mathbf{MR}}\left(10\right)\ne 0$, and ${\mathbf{MR}}\left(7\right)+{\mathbf{MR}}\left(8\right)+{\mathbf{MR}}\left(9\right)=0$, 
or  NPAR is inconsistent with the contents of MR, 
or  WA is too small, 
or  B is too small. 