Torque-free rigid-body invariants (source code)

= Torque-free rigid-body invariants

The <Euler equations for a torque-free rigid body> conserve rotational kinetic energy and squared angular momentum,
$$
E=\frac12\sum_{i=1}^3I_i\omega_i^2,
\qquad
L^2=\sum_{i=1}^3I_i^2\omega_i^2.
$$
Their common level sets are the intersection of two ellipsoids in angular-velocity space.