Approximate controllability-application to approached sentinel
We consider here a semilinear heat equation with the source term as well as the initial and boundary conditions are partially known. We are interesting in a sentinel  problem, which consists in finding the pollution term withou tany attempt of computing the perturbation. We present her some case of approched sentinels. We prove the existence of such sentinel by solving a problem of approximate controllability. To deal with the approximate controllability problem, we make use of the theory of duality in convex optimization following Fenchel-Rockafellar.