Improved error estimates for semidiscrete finite element solutions of parabolic Dirichlet boundary control problems

The parabolic Dirichlet boundary control problem and its finite element discretization are considered in convex polygonal and polyhedral domains. We improve the existing results on the regularity of the solutions by establishing and utilizing the maximal L-p-regularity of parabolic equations under inhomogeneous Dirichlet boundary conditions. Based on the proved regularity of the solutions, we prove O(h(1-1)/q(0-epsilon)) convergence for the semidiscrete finite element solutions for some q(0) > 2, with q(0) depending on the maximal interior angle at the corners and edges of the domain and epsilon being a positive number that can be arbitrarily small.