\[\mathbf{b}=\left[b_{1}(\tau_{0},z_{0}),b_{2}(\tau_{0},z_{0}),b_{1}(\tau_{1},z_%
{1}),b_{2}(\tau_{1},z_{1}),\ldots,b_{1}(\tau_{P-1},z_{P-1}),b_{2}(\tau_{P-1},z%
_{P-1})\right]^{\rm T}.\]