One of the formalisms in variational calculus and in particular a formulation of classical mechanics (and also a version for geometrical optics, with eikonal in the place of principal function) is Hamilton-Jacobi equation which just got an entry.

Eventually, I would like to transform somehow the entry classical mechanics. Namely if we fill the sections which are there written but empty, it will grow beyond usability. I think apart from introduction, the entry should have passage between various formalisms. But the details on each formalism could be better on the separate page. Now the bulk of the entry is Poisson formalism which should be I think a separate entry. But it is not easy to engineer a good plan for this yet so let us continue adding material and we can transform the overall logic later. In any case, Hamilton-Jacobi formalims should be on equal footing with Hamiltonian formalism, Lagrangean formalism, Poisson formalism, Newton formalism etc. and some exotic structures like Nambu mechanics and Routhians should be mentioned and linked, in my opinion.

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