REVIEW 6 minor 46 references
Sparse low-order mortar fluxes let high-order DG methods keep invariant domains on hanging-node adaptive meshes.
Reviewed by Pith at T0; open to challenge. T0 means a machine referee read the full paper against a public rubric. the ladder, T0–T4 →
T0 review · grok-4.5
2026-07-14 16:07 UTC pith:E6HM7JAA
load-bearing objection Clean, correctly scoped fix that finally lets IDP/convex-limiting LGL-DGSEM run on Cartesian AMR with hanging nodes.
Invariant-domain-preserving limiting with Adaptive Mesh Refinement for Legendre-Gauss-Lobatto Discontinuous Galerkin Spectral Element Methods
The pith
A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.
Core claim
On Cartesian meshes with at most one-level hanging-node interfaces, the sparsified mortar fluxes built from LGL-subcell characteristic-function weights are conservative, reduce to the standard local-Lax–Friedrichs flux on conforming faces, fit the graph-viscosity low-order form, and therefore yield an invariant-domain-preserving semi-discrete scheme under an explicit CFL restriction.
What carries the argument
The sparsified low-order mortar fluxes (31)–(32) whose interface weights are integrals of LGL-subcell characteristic functions; these weights produce a compact stencil that still satisfies the discrete metric identities and the bar-state convexity argument.
Load-bearing premise
The construction and the IDP proof hold only for Cartesian meshes, equal polynomial degree on both sides of a mortar, and at most a single level of refinement difference; the operators that transfer the solution during mesh refinement or coarsening are only positivity-stabilized, not proved fully invariant-domain-preserving.
What would settle it
On a 2-to-1 Cartesian mortar with equal polynomial degree, replace the characteristic-function weights by the dense L2-projection mortar weights and check whether the resulting low-order scheme still keeps density and pressure non-negative for every CFL-stable time step on a near-vacuum isentropic vortex or Sedov blast; if it does not, the sparsification claim is essential.
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. The paper constructs sparse, conservative, invariant-domain-preserving (IDP) mortar fluxes for nonconforming interfaces in LGL-DGSEM on Cartesian meshes with hanging nodes (equal polynomial degree, one-level 2-to-1 refinement). Starting from an all-to-all central mortar integral, the authors replace the dense L2-projection weights by non-negative overlap integrals of LGL-subcell characteristic functions, add a local Lax–Friedrichs graph-viscosity term, and obtain interface fluxes (31)–(32) that reduce exactly to the standard conforming LLF flux on matching faces, satisfy discrete metric identities, fit the graph-viscosity low-order form (11), and therefore admit the standard bar-state convex-combination argument for IDP under the CFL restriction (44). The fluxes are then blended with high-order L2-mortar fluxes via a posteriori FCT-type limiting; a Zhang–Shu scaling limiter is applied after AMR transfers. Numerical tests (density-wave and isentropic-flow convergence, Kelvin–Helmholtz, Sedov, Double Mach, high-Mach jet) confirm conservation, expected orders under pure positivity limiting, and robustness on adaptively refined meshes.
Significance. The construction supplies the missing low-order interface operator that allows existing convex-limiting / graph-viscosity DGSEM frameworks to be used with hanging-node AMR. The algebraic derivation is self-contained once the standard LGL-DGSEM and graph-viscosity machinery are granted; conservation, reduction to the conforming case, and the IDP property under the stated CFL follow by direct verification without free parameters. Implementations are provided in the open-source Trixi.jl framework, and the numerical suite includes both order verification and genuinely challenging Euler problems that require positivity and shock capturing. Within the declared Cartesian, equal-degree, one-level setting the result is a clean and useful building block for high-order adaptive simulations of nonlinear hyperbolic systems.
minor comments (6)
- Section 2.2, after (33): a short explicit statement that the sparsified weights remain non-negative and form a partition of unity on both sides of a 2-to-1 interface would make the subsequent bar-state argument completely self-contained without reference to the appendix.
- Remark 6 and Section 3.4: the practical use of the less restrictive low-order CFL together with low-order-solution bounds is well motivated, but a one-sentence clarification that the resulting scheme is no longer provably IDP (only positivity-preserving in practice) would avoid any ambiguity for readers who skip the remark.
- Section 2.4: the Zhang–Shu transfer limiter is correctly described as positivity-stabilizing rather than fully IDP; a brief remark that a fully IDP transfer operator remains open would be helpful.
- Figures 9b, 12a, 13a, 16, 18a: the colour scales for limiting factors and indicator variables are not always labelled; adding a colour bar or a short legend would improve readability.
- A few typographical slips remain (e.g., “adaptivemeshrefinement”, missing spaces after commas in the abstract and introduction, “theso-called”). A careful proof-reading pass would remove them.
- Table 5 and the accompanying text in Appendix A give a useful concrete example of the sparse weights; a one-line reference to this table already in Section 2.2 would help readers who want an immediate illustration of the stencil.
Circularity Check
No significant circularity: the sparsified IDP mortar fluxes are derived algebraically from first principles and reduce to known conforming operators by direct identity, without fitted parameters or load-bearing self-citation chains.
full rationale
The central construction (Section 2.2) begins from a conservative all-to-all mortar surface integral, replaces the dense L2 weights by non-negative LGL-subcell characteristic-function weights that obey the partition-of-unity identities, adds a standard local-Lax–Friedrichs graph-viscosity term, and rewrites the result in the already-established graph-viscosity residual form. Conservation follows at once from antisymmetry of the normals and the weight identities; reduction to the conforming LLF flux is the elementary Kronecker-delta collapse of the characteristic functions on matching interfaces; the bar-state convex-combination argument and the associated CFL restriction are the standard ones already proved for conforming meshes. All steps are purely algebraic identities that hold under the paper’s explicitly declared hypotheses (Cartesian meshes, equal polynomial degree, 2-to-1 hanging-node interfaces). Prior self-citations supply only the volume-limiting machinery and the general IDP framework; they are not used to force the mortar fluxes themselves. No parameters are fitted to data, no uniqueness theorem is imported to exclude alternatives, and no known empirical pattern is merely renamed. The derivation is therefore self-contained.
Axiom & Free-Parameter Ledger
axioms (3)
- domain assumption The low-order graph-viscosity operator with local Lax–Friedrichs viscosity yields bar-states that remain inside any convex invariant set of the hyperbolic system.
- standard math LGL quadrature and the associated diagonal-norm SBP operators satisfy the discrete metric identities on Cartesian elements.
- ad hoc to paper Characteristic functions of the LGL subcells form a partition of unity and produce non-negative overlap weights.
invented entities (1)
-
Sparse mortar weights defined by integrals of LGL-subcell characteristic functions
no independent evidence
read the original abstract
We present an invariant-domain-preserving (IDP) treatment of nonconforming interfaces for Legendre--Gauss--Lobatto Discontinuous Galerkin Spectral Element Methods (LGL-DGSEM) with adaptive mesh refinement (AMR) on Cartesian meshes. The proposed methodology extends recently developed convex limiting and graph-viscosity frameworks for DGSEM to meshes containing hanging nodes. Starting from a conservative mortar formulation, we derive low-order interface fluxes that satisfy the requirements of invariant-domain-preserving discretizations. To avoid the excessive diffusion associated with fully connected mortar couplings, a sparsification strategy based on LGL subcell characteristic functions is introduced, yielding compact interface stencils. The resulting mortar fluxes remain conservative, reduce to the standard conforming formulation on matching interfaces, and naturally fit into graph-viscosity-based low-order schemes used for convex limiting. The proposed construction provides the missing ingredient required to combine high-order DGSEM discretizations, invariant-domain-preserving limiting, and adaptive mesh refinement within a unified framework for nonlinear hyperbolic conservation laws. We provide numerical verifications of the properties of the proposed scheme and run challenging simulations that require positivity limiting and shock-capturing.
Figures
Reference graph
Works this paper leans on
-
[1]
T. C. Fisher, M. H. Carpenter, High-order entropy stable finite difference schemes for nonlinear conservation laws: Finite domains, Journal of Computational Physics 252 (2013) 518–557
2013
-
[2]
G. J. Gassner, A. R. Winters, D. A. Kopriva, Split form nodal discontinuous Galerkin schemes with summation-by-parts property for the compressible Euler equations, Journal of Computational Physics 327 (2016) 39–66
2016
-
[3]
H.Ranocha,M.Schlottke-Lakemper,J.Chan,A.M.Rueda-Ramírez,A.R.Winters,F.Hindenlang,G.J.Gassner, Efficientimplementationof modernentropystableandkineticenergypreservingdiscontinuousGalerkinmethodsforconservationlaws, arXivpreprintarXiv:2112.10517 (2021)
Pith/arXiv arXiv 2021
-
[4]
S. T. Zalesak, Fully multidimensional flux-corrected transport algorithms for fluids, Journal of Computational Physics 31 (1979) 335–362
1979
-
[5]
Selmin, Finite element solution of hyperbolic equations
V. Selmin, Finite element solution of hyperbolic equations. II. Two-dimensional case, Research Report RR-0708, INRIA, 1987
1987
-
[6]
Kuzmin, M
D. Kuzmin, M. Möller, J. N. Shadid, M. Shashkov, Failsafe flux limiting and constrained data projections for equations of gas dynamics, Journal of Computational Physics 229 (2010) 8766–8779
2010
-
[7]
D.Kuzmin,R.Löhner,S.Turek(Eds.),Flux-CorrectedTransport:Principles,Algorithms,andApplications,2ed.,Springer,Dordrecht,2012
2012
-
[8]
C.Lohmann,D.Kuzmin,J.N.Shadid,S.Mabuza, Flux-correctedtransportalgorithmsforcontinuousGalerkinmethodsbasedonhighorder Bernstein finite elements, Journal of Computational Physics 344 (2017) 151–186
2017
-
[9]
R.Löhner,AppliedComputationalFluidDynamicsTechniques:AnIntroductionBasedonFiniteElementMethods,2ed.,JohnWiley&Sons, Chichester, 2008
2008
-
[10]
Kuzmin, H
D. Kuzmin, H. Hajduk, Property-Preserving Numerical Schemes for Conservation Laws, World Scientific, Singapore, 2023. doi:10.1142/ 13466
2023
-
[11]
J. L. Guermond, B. Popov, Invariant domains and first-order continuous finite element approximation for hyperbolic systems, SIAM Journal on Numerical Analysis 54 (2016) 2466–2489
2016
-
[12]
Guermond, M
J.-L. Guermond, M. Nazarov, B. Popov, I. Tomas, Second-order invariant domain preserving approximation of the Euler equations using convex limiting, SIAM Journal on Scientific Computing 40 (2018) A3211–A3239
2018
-
[13]
Guermond, B
J.-L. Guermond, B. Popov, I. Tomas, Invariant domain preserving discretization-independent schemes and convex limiting for hyperbolic systems, Computer Methods in Applied Mechanics and Engineering 347 (2019) 143–175
2019
-
[14]
Pazner, Sparse invariant domainpreserving discontinuous Galerkin methodswith subcell convex limiting, Computer Methods in Applied Mechanics and Engineering 382 (2021) 113876
W. Pazner, Sparse invariant domainpreserving discontinuous Galerkin methodswith subcell convex limiting, Computer Methods in Applied Mechanics and Engineering 382 (2021) 113876
2021
-
[15]
H.Hajduk, MonolithicconvexlimitingindiscontinuousGalerkindiscretizationsofhyperbolicconservationlaws, Computers&Mathematics With Applications 87 (2021) 120–138. Bolm, Rueda-Ramírez, Kuzmin, Gassner:Preprint submitted to ElsevierPage 28 of 30 Invariant-domain-preserving mortar flux for LGL-DGSEM Node𝑗∈ + 𝑆 lower element upper element 0 1 2 3 4 0 1 2 3 4 N...
2021
-
[16]
Hajduk, D
H. Hajduk, D. Kuzmin, T. Kolev, R. Abgrall, Matrix-free subcell residual distribution for Bernstein finite element discretizations of linear advection equations, Computer Methods in Applied Mechanics and Engineering 359 (2020) 112658
2020
-
[17]
A.M.Rueda-Ramírez,W.Pazner,G.J.Gassner, SubcelllimitingstrategiesfordiscontinuousGalerkinspectralelementmethods, Computers & Fluids 247 (2022) 105627
2022
-
[18]
A. M. Rueda-Ramírez, B. Bolm, D. Kuzmin, G. J. Gassner, Monolithic convex limiting for legendre-gauss-lobatto discontinuous galerkin spectral-element methods, Communications on Applied Mathematics and Computation (2024)
2024
-
[19]
D. A. Kopriva, A conservative staggered-grid chebyshev multidomain method for compressible flows. ii. a semi-structured method, Journal of Computational Physics 128 (1996) 475–488
1996
-
[20]
Ranocha, M
H. Ranocha, M. Schlottke-Lakemper, A. R. Winters, E. Faulhaber, J. Chan, G. Gassner, Adaptive numerical simulations with Trixi.jl: A case study of Julia for scientific computing, Proceedings of the JuliaCon Conferences 1 (2022) 77
2022
-
[21]
Schlottke-Lakemper, A
M. Schlottke-Lakemper, A. R. Winters, H. Ranocha, G. J. Gassner, A purely hyperbolic discontinuous Galerkin approach for self-gravitating gas dynamics, Journal of Computational Physics (2021) 110467
2021
-
[22]
M. Schlottke-Lakemper, G. J. Gassner, H. Ranocha, A. R. Winters, J. Chan, A. Rueda-Ramírez, Trixi.jl: Adaptive high-order numerical simulations of hyperbolic PDEs in Julia,https://github.com/trixi-framework/Trixi.jl, 2025. doi:10.5281/zenodo.3996439
-
[23]
Kuzmin, M
D. Kuzmin, M. Möller, S. Turek, High-resolution fem–fct schemes for multidimensional conservation laws, Computer Methods in Applied Mechanics and Engineering 193 (2004) 4915–4946
2004
-
[24]
D.Kuzmin, Entropystabilizationandproperty-preservinglimitersfordiscontinuousGalerkindiscretizationsofnonlinearhyperbolicequations (2020)
2020
-
[25]
Anderson, V
R. Anderson, V. Dobrev, T. Kolev, D. Kuzmin, M. Quezada de Luna, R. Rieben, V. Tomov, High-order local maximum principle preserving (MPP) discontinuous Galerkin finite element method for the transport equation, Journal of Computational Physics 334 (2017) 102–124
2017
-
[26]
D.Kuzmin,M.QuezadadeLuna, Subcellfluxlimitingforhigh-orderBernsteinfiniteelementdiscretizationsofscalarhyperbolicconservation laws, Journal of Computational Physics 411 (2020) 109411
2020
-
[27]
Hennemann, A
S. Hennemann, A. M. Rueda-Ramírez, F. J. Hindenlang, G. J. Gassner, A provably entropy stable subcell shock capturing approach for high order split form DG for the compressible Euler equations, Journal of Computational Physics 426 (2021) 109935
2021
-
[28]
part ii: Subcell finite volume shock capturing, Journal of Computational Physics 444 (2021) 110580
A.M.Rueda-Ramírez,S.Hennemann,F.J.Hindenlang,A.R.Winters,G.J.Gassner, AnentropystablenodaldiscontinuousGalerkinmethod for the resistive mhd equations. part ii: Subcell finite volume shock capturing, Journal of Computational Physics 444 (2021) 110580
2021
-
[29]
A.M.Rueda-Ramírez,G.J.Gassner, Asubcellfinitevolumepositivity-preservinglimiterforDGSEMdiscretizationsoftheEulerequations, arXiv preprint2102.06017 [math.NA](2021). Bolm, Rueda-Ramírez, Kuzmin, Gassner:Preprint submitted to ElsevierPage 29 of 30 Invariant-domain-preserving mortar flux for LGL-DGSEM
Pith/arXiv arXiv 2021
-
[30]
Harten, P
A. Harten, P. D. Lax, B. van Leer, On upstream differencing and Godunov-type schemes for hyperbolic conservation laws, SIAM Review 25 (1983) 35–61
1983
-
[31]
Kuzmin, H
D. Kuzmin, H. Hajduk, A. Rupp, Limiter-based entropy stabilization of semi-discrete and fully discrete schemes for nonlinear hyperbolic problems, Computer Methods in Applied Mechanics and Engineering 389 (2022) 114428
2022
-
[32]
Zhang, C.-W
X. Zhang, C.-W. Shu, Maximum-principle-satisfying and positivity-preserving high-order schemes for conservation laws: Survey and new developments, Proceedings of the Royal Society A: Mathematical Physical and Engineering Sciences 467 (2011) 2752–2776
2011
-
[33]
H.Ranocha,GeneralisedSummation-by-PartsOperatorsandEntropyStabilityofNumericalMethodsforHyperbolicBalanceLaws,Cuvillier Verlag, Göttingen, 2018
2018
-
[34]
C.-W. Shu, S. Osher, Efficient implementation of essentially non-oscillatory shock-capturing schemes, Journal of Computational Physics 77 (1988) 439–471
1988
-
[35]
C.Burstedde,L.C.Wilcox,O.Ghattas,p4est:Scalablealgorithmsforparalleladaptivemeshrefinementonforestsofoctrees, SIAMJournal on Scientific Computing 33 (2011) 1103–1133
2011
-
[36]
Cheng, C.-W
J. Cheng, C.-W. Shu, Positivity-preserving lagrangian scheme for multi-material compressible flow, Journal of Computational Physics 257 (2014) 143–168
2014
-
[37]
F. Vilar, A posteriori correction of high-order discontinuous Galerkin scheme through subcell finite volume formulation and flux reconstruction, Journal of Computational Physics 387 (2019) 245–279
2019
-
[38]
a posteriori
P. Bacigaluppi, R. Abgrall, S. Tokareva, “a posteriori” limited high order and robust schemes for transient simulations of fluid flows in gas dynamics, Journal of Computational Physics 476 (2023) 111898
2023
-
[39]
Löhner, An adaptive finite element scheme for transient problems in cfd, Computer Methods in Applied Mechanics and Engineering 61 (1987) 323–338
R. Löhner, An adaptive finite element scheme for transient problems in cfd, Computer Methods in Applied Mechanics and Engineering 61 (1987) 323–338
1987
-
[40]
Fryxell, K
B. Fryxell, K. Olson, P. Ricker, F. Timmes, M. Zingale, D. Lamb, P. MacNeice, R. Rosner, J. Truran, H. Tufo, Flash: An adaptive mesh hydrodynamics code for modeling astrophysical thermonuclear flashes, The Astrophysical Journal Supplement Series 131 (2000) 273
2000
-
[41]
A. M. Rueda-Ramírez, G. J. Gassner, A flux-differencing formula for split-form summation by parts discretizations of non-conservative systems: Applications to subcell limiting for magneto-hydrodynamics, arXiv preprint arXiv:2211.14009 (2022)
Pith/arXiv arXiv 2022
-
[42]
Woodward, P
P. Woodward, P. Colella, The numerical simulation of two-dimensional fluid flow with strong shocks, Journal of Computational Physics 54 (1984) 115–173
1984
-
[43]
D. Kuzmin, Monolithic convex limiting for continuous finite element discretizations of hyperbolic conservation laws, Computer Methods in Applied Mechanics and Engineering 361 (2020) 112804
2020
-
[44]
Y. Ha, C. L. Gardner, A. Gelb, C.-W. Shu, Numerical simulation of high mach number astrophysical jets with radiative cooling, Journal of Scientific Computing 24 (2005) 29–44
2005
-
[45]
P. Chandrashekar, Kinetic energy preserving and entropy stable finite volume schemes for compressible Euler and Navier–Stokes equations, Communications in Computational Physics 14 (2013) 1252–1286
2013
-
[46]
Bolm, Rueda-Ramírez, Kuzmin, Gassner:Preprint submitted to ElsevierPage 30 of 30
N.Fleischmann,S.Adami,N.A.Adams,Numericalsymmetry-preservingtechniquesforlow-dissipationshock-capturingschemes,Computers & Fluids 189 (2019) 94–107. Bolm, Rueda-Ramírez, Kuzmin, Gassner:Preprint submitted to ElsevierPage 30 of 30
2019
discussion (0)
Sign in with ORCID, Apple, or X to comment. Anyone can read and Pith papers without signing in.