On the equivalence of semi-discrete Active Flux and Discontinuous Galerkin methods and a comparison of their performance

Wasilij Barsukow; Christian Klingenberg; Simon Krotsch

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arXiv · 2603.18160

On the equivalence of semi-discrete Active Flux and Discontinuous Galerkin methods and a comparison of their performance

Wasilij Barsukow·Christian Klingenberg·Simon Krotsch

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Abstract

The Active Flux (AF) method employs a globally continuous approximation, like continuous Finite Element methods. This is achieved through the placement of point values at cell interfaces which are shared between adjacent cells. With, on average, K+1 degrees of freedom per cell, Active Flux achieves a polynomial approximation of degree K+1, while the Discontinuous Galerkin (DG) method uses only polynomials of degree K, i.e. one degree less with the same number of degrees of freedom. Despite all the differences, in this paper we show, however, that for linear problems in one and several dimensions as well as -- in some sense -- for nonlinear ones, semi-discrete AF and DG are the same method. We identify a mapping between their respective degrees of freedom, upon which the updates of these degrees of freedom turn out to agree. On the one hand, AF therefore seems more economical then DG for a given value of the error, and we confirm this in numerical experiments. On the other hand, this is a way to understand superconvergence of DG in a natural way, and we show how Radau polynomials and their zeros appear in the mapping between DG and AF: In the Radau points, AF "shines through" as the background high-order scheme behind DG.

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Wasilij Barsukow, Christian Klingenberg, Simon Krotsch. 2026-03-18. On the equivalence of semi-discrete Active Flux and Discontinuous Galerkin methods and a comparison of their performance. https://arxiv.org/abs/2603.18160

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