v18 - chaos!

Version 18 adds some new commands that let you explore some nice chaotic systems based on examples from Elegant Chaos

dd [damping] [omega] - an animated phase space plot of a forced damped pendulum system
pd [damping] [omega] - an animated Poincaré slice through the same plot as above (shown in picture)
df [damping] [omega] - as dd, but for a forced van der Pol oscillator
pf [damping] [omega] - the Poincaré slice through the above
ds [x_initial] [v_initial] - as dd but for a system with a signum operation in the middle of it
ps [x_initial] [v_initial] - the Poincaré slice through the above