Here $d_1,$dots,$d_4$ are displacements from an equilibrium position, and $u_1,$dots,$u_3$ are forces

acting on the masses. Note that $u_1$ is a tension between the first and second masses,

$u_2$ is a tension between the third and fourth masses, and $u_3$ is a force between the wall

$($at left$)$ and the second mass. You can take the mass and stiffness constants to all be

one: $m_1=$cdots$=m_4=1,k_1=$cdots$=k_4=1.$

$($a$)$ Describe the system as a linear dynamical system with state $(d,d^{})in{R}^8.$