{"title":"Superconvergent and Divergence-Free Mixed Finite Element Methods for the Stokes Equation","authors":"Long Chen, Xuehai Huang, Chao Zhang, Xinyue Zhao","doi":"10.1137/25m1812087","DOIUrl":"https://doi.org/10.1137/25m1812087","url":null,"abstract":"SIAM Journal on Numerical Analysis, Volume 64, Issue 5, Page 1831-1860, October 2026. <br/> Abstract. This paper develops divergence-free mixed finite element methods for the Stokes equation. Using H(div)-conforming velocities and discontinuous pressures ensures the inf-sup condition for the velocity–pressure pair and yields pointwise divergence-free velocities. However, this choice makes the vector Laplacian difficult to discretize. Inspired by mass-conserving mixed formulations with stresses, tangential–normal continuous traceless tensor elements are used to discretize the vector Laplacian. An inf-sup condition for the weak div operator between the stress and velocity spaces is then proved. Two key properties characterize the scheme. First, the stress–velocity inf-sup stability gives a stable discretization of the vector Laplacian without additional stabilization, unlike discontinuous Galerkin or virtual element methods. Second, the scheme has the property that if a stress field is distributionally divergence-free against the discrete divergence-free velocity space, then it is also distributionally divergence-free against the continuous divergence-free velocity space. This property decouples the stress and velocity errors and leads to superconvergence. As a result, optimal-order error estimates are obtained for the stress, while the discrete velocity is superclose to its H(div) interpolant. The projected-pressure error estimate is optimal with Raviart-Thomas velocities and superconvergent with Brezzi-Douglas-Marini velocities, while local postprocessing yields an elementwise divergence-free velocity with higher-order convergence[math]. Numerical experiments confirm the theoretical results.","PeriodicalId":49527,"journal":{"name":"SIAM Journal on Numerical Analysis","volume":"28 1","pages":""},"PeriodicalIF":2.9,"publicationDate":"2026-09-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"148890197","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"Finite Element Analysis of a Nematic Liquid Crystal Landau–de Gennes Model with Quartic Elastic Terms","authors":"Jacob Elafandi, Franziska Weber","doi":"10.1137/24m1694203","DOIUrl":"https://doi.org/10.1137/24m1694203","url":null,"abstract":"SIAM Journal on Numerical Analysis, Volume 64, Issue 5, Page 1795-1830, October 2026. <br/> Abstract. Golovaty et al. [] present a [math]-tensor model for liquid crystal dynamics which reduces to the well-known Oseen–Frank director field model in uniaxial states. This model has been shown to capture phase transitions in nematic liquid crystals. We study a closely related model and present an energy stable scheme for the corresponding gradient flow. We prove well-posedness of the scheme via the Leray-Schauder fixed point theorem and rigorously show the [math]-convergence of discrete minimizers as the mesh size approaches zero. In the numerical experiments, we successfully simulate isotropic-to-nematic phase transitions as expected. We also compare simulations for elastic energies with identical and with highly disparate elastic constants and observe different defect dynamics. A comparison with simulations for the standard Landau–de Gennes model with quadratic energy shows that the quartic model is able to capture richer dynamics than the quadratic model.","PeriodicalId":49527,"journal":{"name":"SIAM Journal on Numerical Analysis","volume":"31 1","pages":""},"PeriodicalIF":2.9,"publicationDate":"2026-09-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"148870247","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
D. Castañón Quiroz, D. A. Di Pietro, J. Droniou, M. Salah
{"title":"A Hybrid High-Order Method for the Power-Law Brinkman Problem with Robust Error Estimates in all Regimes","authors":"D. Castañón Quiroz, D. A. Di Pietro, J. Droniou, M. Salah","doi":"10.1137/25m1778389","DOIUrl":"https://doi.org/10.1137/25m1778389","url":null,"abstract":"SIAM Journal on Numerical Analysis, Volume 64, Issue 4, Page 1764-1793, August 2026. <br/> Abstract. In this work, we propose and analyze a new hybrid high-order method for the Brinkman problem for fluids with power-law viscosity. The proposed method supports general meshes and arbitrary approximation orders and is robust in all regimes, from pure (power-law) Stokes to pure Darcy. Robustness is reflected by error estimates that distinguish the contributions from Stokes- and Darcy-dominated elements as identified by an appropriate dimensionless number and that additionally account for pre-asymptotic orders of convergence. Theoretical results are illustrated by a complete panel of numerical experiments.","PeriodicalId":49527,"journal":{"name":"SIAM Journal on Numerical Analysis","volume":"125 1","pages":""},"PeriodicalIF":2.9,"publicationDate":"2026-08-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"148810012","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"Error Formulas for Block Rational Krylov Approximations of Matrix Functions","authors":"Stefano Massei, Leonardo Robol","doi":"10.1137/25m1751815","DOIUrl":"https://doi.org/10.1137/25m1751815","url":null,"abstract":"SIAM Journal on Numerical Analysis, Volume 64, Issue 4, Page 1733-1763, August 2026. <br/> Abstract. This paper investigates explicit expressions for the error associated with the block rational Krylov approximation of matrix functions. Two formulas are proposed, both derived from characterizations of the residual of the block full orthogonal method. The first formula employs a block generalization of the residual polynomial, while the second leverages the block collinearity of the residuals. A posteriori error bounds based on the knowledge of spectral information of the argument are derived and tested on a set of examples. Notably, both error formulas and their corresponding upper bounds do not require the use of quadratures for their practical evaluation.","PeriodicalId":49527,"journal":{"name":"SIAM Journal on Numerical Analysis","volume":"38 1","pages":""},"PeriodicalIF":2.9,"publicationDate":"2026-08-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"148767950","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"A Posteriori Error Estimates for Parabolic Partial Differential Equations on Stationary Surfaces","authors":"Balázs Kovács, Michael Lantelme","doi":"10.1137/25m1784466","DOIUrl":"https://doi.org/10.1137/25m1784466","url":null,"abstract":"SIAM Journal on Numerical Analysis, Volume 64, Issue 4, Page 1705-1732, August 2026. <br/> Abstract. This paper develops and discusses a residual-based a posteriori error estimator for parabolic surface partial differential equations on closed stationary surfaces. The full discretization uses the surface finite element method in space and the backward Euler method in time. The proposed error indicator bounds the error quantities globally in space from above and below, and globally in time from above and locally from below. Based on the derived error indicator, a space-time adaptive algorithm is proposed. Numerical experiments illustrate and complement the theory.","PeriodicalId":49527,"journal":{"name":"SIAM Journal on Numerical Analysis","volume":"59 1","pages":""},"PeriodicalIF":2.9,"publicationDate":"2026-08-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"148754696","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"Error Estimates of an Exponential Wave Integrator for the Nonlinear Schrödinger Equation with Singular Potential","authors":"Weizhu Bao, Chushan Wang","doi":"10.1137/25m1748317","DOIUrl":"https://doi.org/10.1137/25m1748317","url":null,"abstract":"SIAM Journal on Numerical Analysis, Volume 64, Issue 4, Page 1682-1704, August 2026. <br/> Abstract. In this paper we analyze a first-order exponential wave integrator (EWI) for the nonlinear Schrödinger equation (NLSE) with a singular potential that is locally in [math], which might be locally unbounded. A typical example is the inverse power potential such as the Coulomb potential, which is the most fundamental potential in quantum physics and chemistry. We prove that, under the assumption of [math]-potential and [math]-initial data, the [math]-norm convergence of the EWI is, roughly, first-order in one dimension (1D) and two dimensions (2D), and [math]-order in three dimensions (3D). In addition, under a stronger integrability assumption of [math]-potential for some [math] in 3D, the [math]-norm convergence increases to almost [math]-order if [math] and becomes first-order if [math]. In particular, our results show, to the best of our knowledge for the first time, that first-order [math]-norm convergence can be achieved when solving the NLSE with the Coulomb potential in 3D. The key advancements are the use of discrete (in time) Strichartz estimates, which allow us to handle the loss of integrability due to the singular potential that does not belong to [math], and the more favorable local truncation error of the EWI, which requires no (spatial) smoothness of the potential. Extensive numerical results in 1D, 2D, and 3D are reported to confirm our error estimates and to show the sharpness of our assumptions on the regularity of the singular potentials.","PeriodicalId":49527,"journal":{"name":"SIAM Journal on Numerical Analysis","volume":"42 1","pages":""},"PeriodicalIF":2.9,"publicationDate":"2026-08-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"148717842","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"Mixed FEM for Coupled Unsteady Fluid Flow Problems with [math]-Type Brinkman–Forchheimer Framework and its Application for Reverse-Osmosis Desalination","authors":"Zeinab Gharibi, Mostafa Abbaszadeh, Mehdi Dehghan","doi":"10.1137/25m1767650","DOIUrl":"https://doi.org/10.1137/25m1767650","url":null,"abstract":"SIAM Journal on Numerical Analysis, Volume 64, Issue 4, Page 1645-1681, August 2026. <br/> Abstract. This work analyzes a fully discrete mixed finite element method in a Banach space framework for solving nonstationary coupled fluid flow problems modeled by the Brinkman–Forchheimer equations, with applications to reverse osmosis. The model couples unsteady [math]-type convective Brinkman–Forchheimer and transport equations with nonlinear boundary conditions across a semipermeable membrane. A mixed formulation is used for both the fluid equation (pseudostress-velocity) and the transport equation (concentration, its gradient, and a Lagrange multiplier from the membrane condition). The continuous problem is reformulated in Banach spaces as a fixed-point problem, enabling a well-posedness analysis via differential-algebraic system theory. Spatial discretization employs lowest-order Raviart–Thomas elements for fluxes and piecewise constants for primal variables, while linear elements are used for the Lagrange multiplier. A fully discrete Galerkin scheme with backward Euler time-stepping is proposed. Its well-posedness and stability are proven using a fixed-point argument, and optimal convergence rates are established. Numerical results confirm the theoretical error estimates and demonstrate the method’s effectiveness.","PeriodicalId":49527,"journal":{"name":"SIAM Journal on Numerical Analysis","volume":"29 1","pages":""},"PeriodicalIF":2.9,"publicationDate":"2026-08-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"148728086","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"A Surface Finite Element Scheme for a Stochastic PDE on an Evolving Curve","authors":"Paola Pozzi, Björn Stinner","doi":"10.1137/25m1774173","DOIUrl":"https://doi.org/10.1137/25m1774173","url":null,"abstract":"SIAM Journal on Numerical Analysis, Volume 64, Issue 4, Page 1582-1620, August 2026. <br/> Abstract. In this paper we consider an evolving surface finite element method method for the advection and diffusion of a scalar quantity on a moving closed curve. The diffusion process is controlled by a forcing term that may include a rough term (specifically a stochastic noise) which in particular destroys the classical time differentiability properties of the solution. We provide a suitable variational solution concept and a fully discrete finite element method discretization. Our error analysis appropriately generalizes classical estimates to this weaker setting. We present some numerical simulations that confirm our theoretical findings.","PeriodicalId":49527,"journal":{"name":"SIAM Journal on Numerical Analysis","volume":"26 1","pages":""},"PeriodicalIF":2.9,"publicationDate":"2026-08-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"148703556","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Rishi Das, Harsha Hutridurga, Amiya K. Pani, Ricardo Ruiz-Baier
{"title":"Robust Stability and Preconditioning of Darcy–Forchheimer Equations","authors":"Rishi Das, Harsha Hutridurga, Amiya K. Pani, Ricardo Ruiz-Baier","doi":"10.1137/25m1816115","DOIUrl":"https://doi.org/10.1137/25m1816115","url":null,"abstract":"SIAM Journal on Numerical Analysis, Volume 64, Issue 4, Page 1621-1644, August 2026. <br/> Abstract. We derive parameter-robust quasi-optimal error estimates for mixed finite element methods for the nonlinear Darcy–Forchheimer equations with mixed boundary conditions. Using the framework of operator preconditioning, we also design efficient block preconditioners for the linearized system that exhibit robustness with respect to the coefficients that modulate permeability and inertia of the system. The properties of the formulation (parameter and mesh-size independence of the convergence rates) are illustrated by means of several numerical examples.","PeriodicalId":49527,"journal":{"name":"SIAM Journal on Numerical Analysis","volume":"158 1","pages":""},"PeriodicalIF":2.9,"publicationDate":"2026-08-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"148703559","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"Theory and Internal Structure of ADER-DG Method for Ordinary Differential Equations","authors":"Ivan S. Popov","doi":"10.1137/25m1787008","DOIUrl":"https://doi.org/10.1137/25m1787008","url":null,"abstract":"SIAM Journal on Numerical Analysis, Volume 64, Issue 4, Page 1561-1581, August 2026. <br/> Abstract. Investigation of the approximation properties, convergence, and stability of the Arbitrary higher-order DERivatives discontinuous Galerkin (ADER-DG) method for solving an ODE system is carried out. The ADER-DG method is [math]- and [math]-stable, [math]-stable, [math]- and [math]-stable, and algebraically stable. Several other relations useful for an application and implementation of the ADER-DG method are proved. Applications of the ADER-DG method demonstrated compliance with the expected theoretical results.","PeriodicalId":49527,"journal":{"name":"SIAM Journal on Numerical Analysis","volume":"59 1","pages":""},"PeriodicalIF":2.9,"publicationDate":"2026-08-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"148675386","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}