An affine itemtive system has the form $\mathbf{u}^{(k+1)}=T \mathbf{u}^{(k)}+\mathbf{b}, \mathbf{u}^{(0)}=\mathbf{c}$.
(a) Under what conditions does the system have an equilibrium solution $\mathbf{u}^{(k)} \equiv \mathbf{u}^{\star}$ ?
(b) In such cases, find a formula for the general solution. Hint: Look at $\mathbf{v}^{(k)}=\mathbf{u}^{(k)}-\mathbf{u}^*$.
(c) Solve the following affine iterative systems:
(i) $\mathbf{u}^{(k+1)}=\left(\begin{array}{rr}6 & 3 \\ -3 & -4\end{array}\right) \mathbf{u}^{(k)}+\left(\begin{array}{l}1 \\ 2\end{array}\right), \quad \mathbf{u}^{(0)}=\left(\begin{array}{r}4 \\ -3\end{array}\right)$,
(ii) $\mathbf{u}^{(k+1)}=\left(\begin{array}{rr}-1 & 2 \\ 1 & -1\end{array}\right) \mathbf{u}^{(k)}+\left(\begin{array}{l}1 \\ 0\end{array}\right), \quad \mathbf{u}^{(0)}=\left(\begin{array}{l}0 \\ 1\end{array}\right)$.
(iki) $\mathbf{u}^{(k+1)}=\left(\begin{array}{rrr}-3 & 2 & -2 \\ -6 & 4 & -3 \\ 12 & -6 & -5\end{array}\right) \mathbf{u}^{(k)}+\left(\begin{array}{r}1 \\ -3 \\ 0\end{array}\right), \quad \mathbf{u}^{(0)}=\left(\begin{array}{r}1 \\ 0 \\ -1\end{array}\right)$,
(iv) $\mathbf{u}^{(k+1)}=\left(\begin{array}{rrr}-\frac{5}{6} & \frac{1}{3} & -\frac{1}{6} \\ 0 & -\frac{1}{2} & \frac{1}{3} \\ 1 & -1 & \frac{2}{3}\end{array}\right) \mathbf{u}^{(k)}+\left(\begin{array}{r}\frac{1}{6} \\ -\frac{1}{3} \\ -\frac{1}{2}\end{array}\right), \quad \mathbf{u}^{(0)}=\left(\begin{array}{r}\frac{1}{6} \\ -\frac{2}{3} \\ \frac{1}{3}\end{array}\right)$.
(d) Discuss what happens in cases in which there is no fixed point, assuming that $T$ is complete.