It is said that L(x,u, Del u) is a null Lagrangian if and only if the corresponding integral functional E(u)= integral OmegaL(x,u, Del u) dx has the property that E(u+ phi )=E(u) For all phi in C0 infinity( Omega ), for any choice of u in C1( Omega ). In the homogeneous case, corresponding to L(x,u, Del u)= Phi ( Del u), it is known that a necessary and sufficient condition for L to be a null Lagrangian is that Phi ( Del u) is an affine combination of subdeterminants of Del u of all orders. The authors show that all inhomogeneous null Lagrangians may be constructed from these homogeneous ones by introducing appropriate potentials.
ASJC Scopus subject areas
- Statistical and Nonlinear Physics
- Mathematical Physics
- Physics and Astronomy(all)
- Applied Mathematics