### ERROR ESTIMATES FOR SPARSE OPTIMAL CONTROL PROBLEMS BY PIECEWISE LINEAR FINITE ELEMENT APPROXIMATION

Xiaoliang Song1, Bo Chen2, Bo Yu3

1. 1. Dalian University of Technology, Dalian 116024, China;
2. Department of Mathematics, National University of Singapore, 10 Lower Kent Ridge Road, Singapore;
3. School of Mathematical Sciences, Dalian University of Technology, Dalian 116024, China
• Received:2017-09-04 Revised:2017-09-04 Published:2021-04-12
• Contact: Bo Yu,Email:yubo@dlut.edu.cn
• Supported by:
The authors would like to thank Prof. Defeng Sun at The Hong Kong Polytechnic University and Prof. Kim-Chuan Toh at National University of Singapore for their valuable suggestions that led to improvement in this paper.

Xiaoliang Song, Bo Chen, Bo Yu. ERROR ESTIMATES FOR SPARSE OPTIMAL CONTROL PROBLEMS BY PIECEWISE LINEAR FINITE ELEMENT APPROXIMATION[J]. Journal of Computational Mathematics, 2021, 39(3): 471-492.

Optimization problems with L1-control cost functional subject to an elliptic partial differential equation (PDE) are considered. However, different from the finite dimensional l1-regularization optimization, the resulting discretized L1-norm does not have a decoupled form when the standard piecewise linear finite element is employed to discretize the continuous problem. A common approach to overcome this difficulty is employing a nodal quadrature formula to approximately discretize the L1-norm. In this paper, a new discretized scheme for the L1-norm is presented. Compared to the new discretized scheme for L1-norm with the nodal quadrature formula, the advantages of our new discretized scheme can be demonstrated in terms of the order of approximation. Moreover, finite element error estimates results for the primal problem with the new discretized scheme for the L1-norm are provided, which confirms that this approximation scheme will not change the order of error estimates. To solve the new discretized problem, a symmetric Gauss-Seidel based majorized accelerated block coordinate descent(sGS-mABCD) method is introduced to solve it via its dual. The proposed sGS-mABCD algorithm is illustrated at two numerical examples. Numerical results not only confirm the finite element error estimates, but also show that our proposed algorithm is efficient.

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