Radiant and coradiant dualities

We associate a dual problem to a constrained optimization problem in which the ob-jective is quasiconvex and either attains at 0 its global minimum or its global maximum. The attractive features of such a duality are that it does not require an additional pa-rameter to set the dual and that the dual problem has a form which is similar to the one of the primal problem. We present conditions ensuring strong duality using separation properties. We relate our approach to the Lagrangian theory. Key words Coradiant set. Coradiant function, dual problem. Even convexity. Lagrangian. Quasiconvexity. Radiant set. Radiant function.