A relaxed localized trust-region reduced basis approach for optimization of multiscale problems
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In this contribution, we introduce and analyze a new relaxed and localized version of the trust-region method for PDE-constrained parameter optimization in the context of multiscale problems. As an underlying efficient discretization framework, we rely on the Petrov-Galerkin localized orthogonal decomposition method and its recently introduced two-scale reduced basis approximation. We derive efficient localizable a posteriori error estimates for the primal and dual equations of the optimality system, as well as for the two-scale reduced objective functional. While the relaxation of the outer trust-region optimization loop still allows for a rigorous convergence result, the resulting method converges much faster due to larger step sizes in the initial phase of the iterative algorithms. The resulting algorithm is parallelized in order to take advantage of the localization. Numerical experiments are given for a multiscale thermal block benchmark problem. The experiments demonstrate the efficiency of the approach, particularly for large scale problems, where methods based on traditional finite element approximation schemes are prohibitive or fail entirely.
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