Spectral separation of variables from equivalent Lagrangian systems
This paper demonstrates that requiring two quadratic Lagrangians to generate identical Euler-Lagrange equations imposes a commutation condition between their kinetic matrices and the potential's Hessian, which enables an orthogonal spectral decomposition of the configuration space to decouple the equations of motion into independent subsystems, thereby recovering classical integrable regimes in systems like Sawada-Kotera and Hénon-Heiles.