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arXiv · 1801.06888

On Lagrangians with Reduced-Order Euler-Lagrange Equations

David Saunders
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Abstract

If a Lagrangian defining a variational problem has order $k$ then its Euler-Lagrange equations generically have order $2k$. This paper considers the case where the Euler-Lagrange equations have order strictly less than $2k$, and shows that in such a case the Lagrangian must be a polynomial in the highest-order derivative variables, with a specific upper bound on the degree of the polynomial. The paper also provides an explicit formulation, derived from a geometrical construction, of a family of such $k$-th order Lagrangians, and it is conjectured that all such Lagrangians arise in this way.

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David Saunders. 2018-01-21. On Lagrangians with Reduced-Order Euler-Lagrange Equations. https://doi.org/10.3842/sigma.2018.089

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