Error estimates of triangular mixed finite element methods for distributed parameter systems

This goal of this paper is to study a priori error estimates of triangular mixed finite element methods for distributed parameter systems. The state and the co-state are discretized by the lowest order Raviart-Thomas mixed finite element spaces and the control is discretized by piecewise constant functions. We derive a priori error estimates for the coupled state and control approximation. Finally, we present an numerical example which confirm our theoretical results.