Solve Lagrange's equations for a famous chaotic pendulum (as on
exhibit at the San Francisco Exploratorium). Run a movie of the
result. By default, the movie runs for 60 seconds, but if you
supply an argument to the demo3 function, it will run for that
The kick= keyword may be used to adjsut the initial amplitude;
kick= 1.2 is the default.
You may also wish to supply a damp_time= keyword to see the effect
of an ad hoc damping term. damp_time=100 is nice.
interpreted function, defined at i/demo3.i line 10