Communications on Applied Mathematics and Computation ›› 2025, Vol. 7 ›› Issue (2): 411-425.doi: 10.1007/s42967-023-00330-5

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Constructing a CDG Finite Element with Order Two Superconvergence on Rectangular Meshes

Xiu Ye1, Shangyou Zhang2   

  1. 1 Department of Mathematics, University of Arkansas at Little Rock, Little Rock, AR 72204, USA;
    2 Department of Mathematical Sciences, University of Delaware, Newark, DE 19716, USA
  • Received:2023-04-25 Revised:2023-08-08 Accepted:2023-09-28 Online:2025-06-20 Published:2025-04-21

Abstract: A novel conforming discontinuous Galerkin (CDG) finite element method is introduced for Poisson equation on rectangular meshes. This CDG method with discontinuous Pk (k ≥ 1) elements converges to the true solution two orders above the continuous finite element counterpart. Superconvergence of order two for the CDG finite element solution is proved in an energy norm and the L2 norm. A local post-process is defined which lifts a Pk CDG solution to a discontinuous Pk+2 solution. It is proved that the lifted Pk+2 solution converges at the optimal order. The numerical tests illustrate the theoretic findings.

Key words: Finite element, Conforming discontinuous Galerkin (CDG) method, Stabilizer free, Rectangular mesh, Superconvergent

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