Must there exist a Lagrangian for any 2nd order ordinary derivative equation?
44282
How do I show that there exists variational/action principle for a given classical system?
885
Why is the 2nd derivative written as $\frac{\mathrm d^2y}{\mathrm dx^2}$?
75612
Why are differential equations for fields in physics of order two?
138908
Most general Lagrangian in CFT in 0+1D
59279
Example of function that is differentiable, but the second derivative is not defined
17414
Lagrangian of an effective potential
156942
Square of a second derivative is the fourth derivative
117338
Counterexample to second derivative test when f''(x) is not continuously differentiable
96022
Symmetry of second derivative - Sufficiency of twice-differentiability
13312
Is there something similar to Noether's theorem for discrete symmetries?
4421
Proof that total derivative is the only function that can be added to Lagrangian without changing the EOM
136692
Why should the spatial derivative order of the ODE *not* exceed two?
63473
Is the shorthand $ \partial_{\mu} $ strictly a partial derivative in field theory?
64727
Total time derivatives and partial coordinate derivatives in classical mechanics
125738
Names of higher-order derivatives
96880
How to obtain Hamiltonian formalism and phase space for Lagrangian with second-derivatives?
84689
solving third-order nonlinear ordinary differential equation