Wednesday, 11 November 2015

classical mechanics - Invariance of Lagrangian in Noether's theorem


Often in textbooks Noether's theorem is stated with the assumption that the Lagrangian needs to be invariant δL=0.


However, given a lagrangian L, we know that the Lagrangians αL (where α is any constant) and L+dfdt (where f is any function) lead to the same equations of motion.


Can we then consider that the Lagrangian is invariant under a transformation if we find δL=αL or δL=dfdt instead of δL=0?




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