Kogan, Irina A.Olver, Peter J.2007-08-162007-08-162000-12https://hdl.handle.net/11299/3517In this paper, we derive an explicit group-invariant formula for the Euler-Lagrange equations associated with an invariant variational problem. The method relies on a group-invariant version of the variational bicomplex that is based on a general moving frame construction and is of independent interest.