On the role of semismoothness in nonsmooth numerical analysis: Theory

For the numerical solution of nonsmooth problems, sometimes it is not necessary that an exact subgradient/generalized Jacobian is at our disposal, but that a certain semismoothness property is fulfilled. In this paper we consider not only semismoothness of nonsmooth real- and vector-valued mappings, but also its interplay with the semismoothness^* property for multifunctions. In particular, we are interested in the semismoothness of solution maps to parametric semismooth^* inclusions. Our results are expressed in terms of suitable generalized derivatives of the set-valued part, i.e., by limiting coderivatives or by SC (subspace containing) derivatives. As a byproduct we identify a class of multifunctions having the remarkable property that they are strictly proto-differentiable almost everywhere (with respect to some Hausdorff measure) on their graph.