
<p style='text-indent:20px;'>We analyze superconvergence property of the lowest order curl-curl conforming finite element method based on polynomial preserving recovery (PPR) for the two-dimensional quad-curl problem on triangular meshes. We observe that the linear interpolation of <inline-formula><tex-math id="M1">\begin{document}$ \nabla \times \boldsymbol u_h $\end{document}</tex-math></inline-formula> (<inline-formula><tex-math id="M2">\begin{document}$ \boldsymbol u_h $\end{document}</tex-math></inline-formula> is the numerical solution) can be written as a linear combination of solutions of two discrete Poisson equations obtained by the usual linear finite element method. Therefore, the superconvergence analysis of the quad-curl problem can be attributed to the analysis of the Poisson equation. Then, with the help of the existing superconvergence results for the Poisson equation, we prove that recovered <inline-formula><tex-math id="M3">\begin{document}$ \nabla \times \nabla \times \boldsymbol u_h $\end{document}</tex-math></inline-formula> (by applying PPR to <inline-formula><tex-math id="M4">\begin{document}$ \nabla \times \boldsymbol u_h $\end{document}</tex-math></inline-formula>) is superconvergent to <inline-formula><tex-math id="M5">\begin{document}$ \nabla \times \nabla \times \boldsymbol u $\end{document}</tex-math></inline-formula>. Based on this superconvergent result, we derive an asymptotically exact <i>a posteriori</i> error estimator. Numerical tests are provided to demonstrate effectiveness of the proposed method and confirm our theoretical findings.</p>
superconvergence, \textit{a posteriori} error estimate, Error bounds for boundary value problems involving PDEs, Laplace operator, Helmholtz equation (reduced wave equation), Poisson equation, adaptive, Rate of convergence, degree of approximation, quad-curl problem, Finite element, Rayleigh-Ritz and Galerkin methods for boundary value problems involving PDEs, Stability and convergence of numerical methods for boundary value problems involving PDEs, polynomial preserving recovery, Mesh generation, refinement, and adaptive methods for boundary value problems involving PDEs
superconvergence, \textit{a posteriori} error estimate, Error bounds for boundary value problems involving PDEs, Laplace operator, Helmholtz equation (reduced wave equation), Poisson equation, adaptive, Rate of convergence, degree of approximation, quad-curl problem, Finite element, Rayleigh-Ritz and Galerkin methods for boundary value problems involving PDEs, Stability and convergence of numerical methods for boundary value problems involving PDEs, polynomial preserving recovery, Mesh generation, refinement, and adaptive methods for boundary value problems involving PDEs
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