Abstract
Filtering plays a crucial role in postprocessing and analyzing data in scientific and engineering applications. Various application-specific filtering schemes have been proposed based on particular design criteria. In this paper, we focus on establishing the theoretical connection between quasi-interpolation and a class of kernels (based on B-splines) that are specifically designed for the postprocessing of the discontinuous Galerkin (DG) method called smoothness-increasing accuracy-conserving (SIAC) filtering. SIAC filtering, as the name suggests, aims to increase the smoothness of the DG approximation while conserving the inherent accuracy of the DG solution (superconvergence). Superconvergence properties of SIAC filtering has been studied in the literature. In this paper, we present the theoretical results that establish the connection between SIAC filtering to long-standing concepts in approximation theory such as quasi-interpolation and polynomial reproduction. This connection bridges the gap between the two related disciplines and provides a decisive advancement in designing new filters and mathematical analysis of their properties. In particular, we derive a closed formulation for convolution of SIAC kernels with polynomials. We also compare and contrast cardinal spline functions as an example of filters designed for image processing applications with SIAC filters of the same order, and study their properties.
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Notes
The negative order norm \(\Vert \cdot \Vert _{-\ell , \varOmega }\) is the norm associated with \(H^{-\ell }(\varOmega )\) (i.e., the dual space of the Sobolev space \(H^\ell (\varOmega )\)).
The first-order central B-spline is often denoted as \(b_0(x)\), but herein the authors chose to follow the notation used in the previously published definition of SIAC kernels throughout the article.
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Acknowledgments
The authors wish to thank Dr. Hanieh Mirzaee and Mr. James King for helpful discussion and sharing the symmetric SIAC postprocessing code, Xiaozhou Li for confirming the convergence results and Varun Shankar for useful suggestions. The authors are sponsored in part by the Air Force Office of Scientific Research (AFOSR), Computational Mathematics Program (Program Manager: Dr. Fariba Fahroo), under grant number FA9550-12-1-0428 (first and third author) and FA8655-13-1-3017 (second author).
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Mirzargar, M., Ryan, J.K. & Kirby, R.M. Smoothness-Increasing Accuracy-Conserving (SIAC) Filtering and Quasi-Interpolation: A Unified View. J Sci Comput 67, 237–261 (2016). https://doi.org/10.1007/s10915-015-0081-9
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DOI: https://doi.org/10.1007/s10915-015-0081-9