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Existence, Uniqueness and Convergence of Simultaneous Distributed-Boundary Optimal Control Problems

We consider a steady-state heat conduction problem $P$ for the Poisson equation with mixed boundary conditions in a bounded multidimensional domain $Ω$. We also consider a family of problems $P_α$ for the same Poisson equation with mixed boundary conditions being $α>0$ the heat transfer coefficient defined on a portion $Γ_{1}$ of the boundary. We formulate simultaneous \emph{distributed and Neumann boundary} optimal control problems on the internal energy $g$ within $Ω$ and the heat flux $q$, defined on the complementary portion $Γ_{2}$ of the boundary of $Ω$ for quadratic cost functional. Here the control variable is the vector $(g,q)$. We prove existence and uniqueness of the optimal control $(\overline{\overline{g}},\overline{\overline{q}})$ for the system state of $P$, and $(\overline{\overline{g}}_α,\overline{\overline{q}}_α)$ for the system state of $P_α$, for each $α>0$, and we give the corresponding optimality conditions. We prove strong convergence, in suitable Sobolev spaces, of the vectorial optimal controls, system and adjoint states governed by the problems $P_α$ to the corresponding vectorial optimal control, system and adjoint states governed by the problem $P$, when the parameter $α$ goes to infinity. We also obtain estimations between the solutions of these vectorial optimal control problems and the solution of two scalar optimal control problems characterized by fixed $g$ (with boundary optimal control $\overline{q}$) and fixed $q$ (with distributed optimal control $\overline{g}$), respectively, for both cases $α>0$ and $α=\infty$.