Hybridization through the border of the elements (hybrid unknowns) combined with a Schur complement procedure (often called static condensation in the context of continuous Galerkin linear elasticity computations) has in various forms been advocated in the mathematical and engineering literature as a means of accomplishing domain decomposition, of obtaining increased accuracy and convergence results, and of algorithm optimization. Recent work on the hybridization of mixed methods, and in particular of the discontinuous Galerkin (DG) method, holds the promise of capitalizing on the three aforementioned properties; in particular, of generating a numerical scheme that is discontinuous in both the primary and flux variables, is locally conservative, and is computationally competitive with traditional continuous Galerkin (CG) approaches. In this paper we present both implementation and optimization strategies for the Hybridizable Discontinuous Galerkin (HDG) method applied to two dimensional elliptic operators. We implement our HDG approach within a spectral/hp element framework so that comparisons can be done between HDG and the traditional CG approach. We demonstrate that the HDG approach generates a global trace space system for the unknown that although larger in rank than the traditional static condensation system in CG, has significantly smaller bandwidth at moderate polynomial orders. We show that if one ignores set-up costs, above approximately fourth-degree polynomial expansions on triangles and quadrilaterals the HDG method can be made to be as efficient as the CG approach, making it competitive for time-dependent problems even before taking into consideration other properties of DG schemes such as their superconvergence properties and their ability to handle hp-adaptivity.
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Acknowledgements The authors would like to thank Dr. Cuoug Nguyen for his comparative runs which highlighted the asymptotic convergence of the problem examined in Fig. 10(a). The first author gratefully acknowledges the support provided under NSF Career Award NSF-CCF0347791 (R. Kirby), NIH grant 5R01HL067646 (A. Cheung), and the Leverhulme Trust. The second author would like to acknowledge support from Advanced Research Fellowship from EPSRC. The third author would like to acknowledge support from the National Science Foundation (Grant DMS-0712955).
- Discontinuous Galerkin method
- Domain decomposition
- High-order finite elements
- Spectral/hp elements