Set up n particles randomly distributed in a 1/r^2 profile (so that the circular velocity is constant). Truncate the halo at radius of 1Mpc. These particles are all fixed in place.

Put particle in a circular orbit at 0.5 Mpc and evolve for around 30 orbits.

Decrease timestep:

Change softening:

Increase order of multipoles:

Increase number of particles: