Duality in Nonconvex Optimization and Calculus of Variations.
Ivar Ekeland · Defense Technical Information Center (DTIC) · 1976
A general duality theory is given for smooth nonconvex optimization problems, covering both the finite-dimensional case and the calculus of variations. The results are quite similar to the convex case; in particular, with every problem (P) is associated a dual problem (P*) having opposite value.