This is a double rigid-bar pendulum. The bars are of equal length and mass (1 m and 1 kg). Set the initial angles (θ₁ and θ₂) then release the pendulum. Total energy is supposed to be conserved (without damping), but numerical truncation causes the total energy to deviate. There are three integration schemes to try - Euler, Symplectic (Leapfrog), and 4th-order Runge-Kutta. Set the GRAPH option to TRACE to observe the path traced by the bars. Note the chaotic motion under some conditions - a combination of actual chaotic behavior combined with numerical error. If the total energy exceeds 3X the initial total energy, the simulation will stop - try a smaller time step.