marginally stable, equilibrium position and controllability Marginally Stable For a marginally stable system, its response will neither follow the reference nor increase to infinity. The system response will not settle, it will continue to oscillate with constant

amplitude. For a marginally stable system, the roots of the characteristic equation must lie on imaginary axis of the complex plan. Different poles locations on the imaginary axis correspond to different time response curve: - Complex conjugate poles correspond to an oscillatory

transient with constant amplitude - A pole at the origin correspond to a ramp response