International audienceThis paper deals with Mayer's problem for controlled systems with reflection on the boundary of a closed subset K. The main result is the characterization of the possibly discontinuous value function in terms of a unique solution in a suitable sense to a partial differential equation of Hamilton–Jacobi–Bellman type

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International audienceWe study two classes of stochastic control problems with semicontinuous cost: the Mayer problem and optimal stopping for controlled diffusions. The value functions are introduced via linear optimization problems on appropriate sets of probability measures. These sets of constraints are described deterministically with respect to the coefficient functions. Both the lower and upper semicontinuous cases are considered. The value function is shown to be a generalized viscosity solution of the associated HJB system, respectively, of some variational inequality. Dual formulations are given, as well as the relations between the primal and dual value functions. Under classical convexity assumptions, we prove the equivalence between the linearized Mayer problem and the standard weak control formulation. Counter-examples are given for the general framework

The aim of the paper is to provide a linearization approach to the L ∞-control problems. We begin by proving a semigroup-type behaviour of the set of constraints appearing in the linearized formulation of (standard) control problems. As a byproduct we obtain a linear formulation of the dynamic programming principle. Then, we use the L p approach and the associated linear formulations. This seems to be the most appropriate tool for treating L ∞ problems in continuous and lower semicontinuous setting. Mathematics Subject Classification. 34A60, 49J45, 49L20, 49L25, 93C15.