I need to plot a Poincaré map for a double pendulum where the string connecting one mass to the other is elastic with elasticity constant k and rest length s. The equations of motions are:
\dot{\theta}_1=
\frac{p_{\theta_1}}{m_1 r_1^2}
- \frac{p_{\theta_2}}{m_1 r_1 r_2} \cos{(\theta _1-...