FRÉCHET SUBDIFFERENTIAL CALCULUS FOR INTERVAL-VALUED FUNCTIONS AND ITS APPLICATIONS IN NONSMOOTH INTERVAL OPTIMIZATION

To deal with nondifferentiable interval-valued functions (IVFs) (not necessarily convex), we present the notion of Frechet subdifferentiability or gH-Frechet subdifferentiability. We explore its relationship with gH-differentiability and develop various calculus results for gH-Frechet subgradients of extended IVFs. By using the proposed notion of subdifferentiability, we derive new necessary optimality conditions for unconstrained interval optimization problems (IOPs) with nondifferentiable IVFs. We also provide a necessary condition for unconstrained weak sharp minima of an extended IVF in terms of the proposed notion of subdifferentiability. Examples are pesented to support the main results.