Primal-Dual Gradient Structured Functions: Second-Order Results; Links to Epi-Derivatives and Partly Smooth Functions

We give second-order expansions for quite general nonsmooth functions from the $\cal{V}\cal{U}$-space decomposition point of view. The results depend on primal-dual gradient structure, which we relate to general concepts of second-order epi-derivatives and partly smooth functions. Expressions for the associated second-order objects are given in terms of $\cal{U}$-subspace Hessians.