by Deckelnick, K., Guenther, A., Hinze, M..

**Series:** 2007-13, Preprints

- MSC:
- 49J20 Optimal control problems involving partial differential equations
- 49K20 Problems involving partial differential equations

**Abstract:**

We consider an elliptic optimal control problem with

control constraints and pointwise bounds on the gradient of the state. We present a tailored finite element approximation to this optimal control problem, where the cost functional is approximated by a sequence of functionals which are obtained by discretizing the state equation with the help of the lowest order Raviart--Thomas mixed finite element. Pointwise bounds on the gradient variable are enforced in the elements of the triangulation. Controls are not discretized. Error bounds for control and state are obtained in two and three space dimensions. A numerical example confirms our analytical findings.

**Keywords:**

Elliptic optimal control problem, state constraints, error estimates