Chaotic Pendulum in State Space (Gamma=1.2) T-Shirt

Everyone has heard of chaos, but you may not know that even very simple systems can be chaotic. One of the simplest is a pendulum driven by an external force. If it is driven at its natural frequency with some damping it exhibits the period doubling route to chaos. A single parameter (the driving strength "gamma") controls the behaviour. With gamma less than 1, the pendulum makes a deterministic (non-chaotic) closed orbit in state space. This shirt shows the results for gamma=1.2. The circular-ish orbit is still there, but it is not reproducible as the pendulum makes gay sojourns into other regions of state space. This shirt is completely self documenting, including the differential equation being solved and all the parameters that generated it. With the information contained herein, you could write your own code to replicate your shirt exactly (watch out for rounding errors! (chaos joke)). Perfect for a physicist, mathematician or computer scientist on your list.