Double Pendulum ChaosOne rod swings from a pivot; a second swings from the end of the first. That is the whole machine — and it is unpredictable. Here a thousand of them start from almost exactly the same angle; within seconds every one is following a wildly different path.The equations are ordinary Newtonian mechanics, fully deterministic. But the map from starting angle to later position is so steep that rounding the start in the ninth decimal changes the answer — Poincaré's discovery, and the reason weather can't be forecast far ahead.