For animation, the program uses Matlab's normal plot command combined with the drawnow command. It is based on the ode45 solution of the corresponding differential equations.
Comprehensive documentation is provided, including a sketch of the most important steps of how to derive the equations of motion. A simple Mathematica notebook contains all of the manipulations.
Start the program via >> double_pendulum_init
You can adapt parameters such as rod lengths, masses and initial angular positions and velocities in the double_pendulum_init.m file.
It might be interesting to implement some features in future versions, such as angular time dependence plots, phase space portraits or Poincaré sections.
Have fun observing the rich dynamic behaviour of this simple, but mostly chaotic system :-)