Three-body figure-eight choreography

Three equal masses interact under Newtonian gravity in 2D. At the Chenciner-Montgomery initial condition (2000), all three masses chase one another along a single closed figure-eight curve with period T ≈ 6.326. The velocity-Verlet integrator from shared/js/engine/symplectic.js preserves total energy to a part-in-a-million bound and total linear and angular momentum to machine precision. The "dv" slider perturbs the initial velocity of body 3 by a small amount; at dv = 0 the choreography is stable, and at dv = 0.01 the system slowly drifts off the closed curve.