Damped mechanical energy as a Lyapunov function (source code)

= Damped mechanical energy as a Lyapunov function

For $\ddot x=-U'(x)-\mu\dot x$ with $\mu>0$,
$$
E(x,\dot x)=\frac12\dot x^2+U(x),
\qquad
\dot E=-\mu\dot x^2.
$$
If $U$ is radially unbounded, every trajectory is bounded, and LaSalle's principle reduces its omega-limit set to invariant points with zero velocity.