We state a unified geometrical version of the variational principles for second-order classical field theories. The standard Lagrangian and Hamiltonian variational principles and the corresponding field equations are recovered from this unified framework.
CitacióRoman-Roy, N., P.D. Prieto-Martínez. Variational principles for multisymplectic second-order classical field theories. "International journal of geometric methods in modern physics", 01 Setembre 2015, vol. 12, núm. 8.