The Hénon-Heiles equation is a nonlinear nonintegrable Hamiltonian system with x^¨ | = | -(dV)/(dx) y^¨ | = | -(dV)/(dy), where the potential energy function is defined by the polar equation V(r, θ) = 1/2 r^2 + 1/3 r^3 sin(3θ), giving Cartesian potential V(x, y) = 1/2(x^2 + y^2 + 2x^2 y - 2/3 y^3).

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