Gibbs phenomena for L^q-best approximation in finite element spaces^*

¹ School of Mathematical Sciences, The University of Nottingham, University Park, Nottingham NG7 2RD, UK
² Department of Engineering, University of Cambridge, Cambridge CB2 1PZ, UK

^* Corresponding author: sr957@cam.ac.uk

Received: 22 December 2020
Accepted: 16 December 2021

Abstract

Recent developments in the context of minimum residual finite element methods are paving the way for designing quasi-optimal discretization methods in non-standard function spaces, such as q-type Sobolev spaces. For q → 1, these methods have demonstrated huge potential in avoiding the notorious Gibbs phenomena, i.e., the occurrence of spurious non-physical oscillations near thin layers and jump discontinuities. In this work we provide theoretical results that explain some of these numerical observations. In particular, we investigate the Gibbs phenomena for q-best approximations of discontinuities in finite element spaces with 1 ≤ q < ∞. We prove sufficient conditions on meshes in one and two dimensions such that over- and undershoots vanish in the limit q → 1. Moreover, we include examples of meshes such that Gibbs phenomena remain present even for q = 1 and demonstrate that our results can be used to design meshes so as to eliminate the Gibbs phenomenon.