{"title":"Optimality of Quasi-Monte Carlo Methods and Suboptimality of the Sparse-Grid Gauss–Hermite Rule in Gaussian Sobolev Spaces","authors":"Yoshihito Kazashi, Yuya Suzuki, Takashi Goda","doi":"10.1137/25m1794346","DOIUrl":"https://doi.org/10.1137/25m1794346","url":null,"abstract":"SIAM Journal on Numerical Analysis, Volume 64, Issue 5, Page 2123-2150, October 2026. <br/> Abstract. Optimality of several quasi-Monte Carlo methods and suboptimality of the sparse-grid quadrature based on the univariate Gauss–Hermite rule are proved in the Sobolev spaces of mixed dominating smoothness of order [math], where the optimality is in the sense of worst-case convergence rate. For sparse-grid Gauss–Hermite quadrature, lower and upper bounds are established, with rates coinciding up to a logarithmic factor. This common algebraic rate is found to be only [math] with [math] function evaluations, although the optimal rate is known to be [math]. The lower bound is obtained by exploiting the structure of the Gauss–Hermite nodes and is independent of the quadrature weights; consequently, no modification of the weights can improve the rate [math]. In contrast, several quasi-Monte Carlo methods with a change of variables are shown to achieve the optimal rate, some up to, and one including, the logarithmic factor.","PeriodicalId":49527,"journal":{"name":"SIAM Journal on Numerical Analysis","volume":"34 1","pages":""},"PeriodicalIF":2.9,"publicationDate":"2026-10-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"149208470","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 Error Analysis for Elliptic Parameter Identification with Power-Type Nonlinearity","authors":"De-Han Chen, Yi-Hsuan Lin, Irwin Yousept","doi":"10.1137/26m1842646","DOIUrl":"https://doi.org/10.1137/26m1842646","url":null,"abstract":"SIAM Journal on Numerical Analysis, Volume 64, Issue 5, Page 2151-2176, October 2026. <br/> Abstract. This paper studies the numerical analysis of a parameter identification problem governed by elliptic equations with power-type nonlinearity. We propose a numerical reconstruction via a suitable least-squares minimization problem based on piecewise linear finite elements. As one of our main novelties, we establish conditional stability estimates at the continuous level, which form the theoretical foundation of the present finite element analysis. Our stability analysis relies on tailored analytical tools, including Hardy-type inequalities, fractional Gagliardo–Nirenberg inequalities, and weighted spaces with singular distance weights. By invoking the achieved conditional stability together with the Carstensen quasi-interpolation operator and associated estimates in negative Sobolev spaces, we derive a priori error estimates for the proposed finite element approximation in terms of the mesh size, the regularization parameter, the noise level, and the nonlinearity exponent. Our results extend the recent stability and error estimates for the linear case by Jin et al. [] and sharpen their error estimates and convergence order under weaker regularity assumptions.","PeriodicalId":49527,"journal":{"name":"SIAM Journal on Numerical Analysis","volume":"13 1","pages":""},"PeriodicalIF":2.9,"publicationDate":"2026-10-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"149187909","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":"Density Estimation via Periodic Scaled Korobov Kernel Method with Exponential Decay Condition","authors":"Ziyang Ye, Haoyuan Tan, Xiaoqun Wang, Zhijian He","doi":"10.1137/25m1770370","DOIUrl":"https://doi.org/10.1137/25m1770370","url":null,"abstract":"SIAM Journal on Numerical Analysis, Volume 64, Issue 5, Page 2100-2122, October 2026. <br/> Abstract. We propose the periodic scaled Korobov kernel (PSKK) method for nonparametric density estimation on [math]. By first wrapping the target density into a periodic version through modulo operation and subsequently applying kernel ridge regression in scaled Korobov spaces, we extend the kernel approach proposed by Kazashi and Nobile [SIAM J. Numer. Anal., 61 (2023), pp. 1080–1102] and eliminate its requirement for inherent periodicity of the density function. This key modification enables effective estimation of densities defined on unbounded domains. We establish rigorous mean integrated squared error (MISE) bounds, proving that for densities with smoothness of order [math] and exponential decay, our PSKK method achieves an [math] MISE convergence rate with an arbitrarily small [math]. While matching the convergence rate of the previous kernel approach, our method applies to nonperiodic distributions at the cost of stronger differentiability and exponential decay assumptions. Numerical experiments confirm the theoretical results and demonstrate a significant improvement over traditional kernel density estimation in large-sample regimes.","PeriodicalId":49527,"journal":{"name":"SIAM Journal on Numerical Analysis","volume":"33 1","pages":""},"PeriodicalIF":2.9,"publicationDate":"2026-10-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"149152577","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 Dichotomy of Finite Element Spaces and Its Application to an Energy-Conservative Scheme for the Regularized Long Wave Equation","authors":"Dimitrios Antonopoulos, Dimitrios Mitsotakis","doi":"10.1137/25m1834740","DOIUrl":"https://doi.org/10.1137/25m1834740","url":null,"abstract":"SIAM Journal on Numerical Analysis, Volume 64, Issue 5, Page 2079-2099, October 2026. <br/> Abstract. Certain energy-conservative Galerkin discretizations for nonlinear dispersive wave equations have revealed an unusual convergence behavior: optimal convergence is attained when continuous Lagrange finite element spaces of odd polynomial degree are employed, whereas the use of even-degree polynomials leads to reduced convergence rate. The present work demonstrates that this behavior is intrinsic to the structure of the finite element spaces themselves. In particular, it is shown to be closely connected to the standard [math]-projection of derivatives, which possesses a super-approximation property exclusively for odd polynomial degrees. We also examine the implications of this feature for an energy-conservative Galerkin approximation of the regularized long-wave equation where the energy is a cubic functional. Although the resulting scheme conserves both mass and energy, we further show that the impulse is approximated with high accuracy, and we establish a priori error bounds for the associated semidiscrete formulation.","PeriodicalId":49527,"journal":{"name":"SIAM Journal on Numerical Analysis","volume":"30 1","pages":""},"PeriodicalIF":2.9,"publicationDate":"2026-09-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"149043592","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":"An ({hp})-Version Time Stepping Spectral Monte Carlo Method for Semi-linear Parabolic Equations","authors":"Jiaying Feng, Zhiyuan Hui, Changtao Sheng, Chenglong Xu","doi":"10.1137/25m1787045","DOIUrl":"https://doi.org/10.1137/25m1787045","url":null,"abstract":"SIAM Journal on Numerical Analysis, Volume 64, Issue 5, Page 2051-2078, October 2026. <br/> Abstract. In this paper, we present an [math]-version time-stepping spectral Monte Carlo method for solving semilinear parabolic equations. The key innovation lies in constructing an exponentially accurate stochastic algorithm that integrates a residual iteration scheme on Gauss-type nodes in both temporal and spatial directions with a reconstruction strategy rooted in spectral methods. To address the long-time simulations and initial singularities that are often challenging for traditional stochastic algorithms (e.g., walk-on-spheres method), we further develop an [math]-version time-stepping framework that employs multiple time steps and, respectively, geometric time partitions with linearly increasing polynomial degrees to handle these difficulties. Notably, the proposed algorithm bypasses the need to solve linear systems required by traditional spectral methods and remarkably supports parallel computation at both temporal and spatial grid points. We rigorously establish exponential convergence rates for the multistep method within a finite number of iterations. Extensive numerical experiments are conducted to demonstrate the spectral accuracy and computational efficiency of the proposed method in long-time simulations, problems with initial singularities, and a five-dimensional problem, thereby validating the theoretical results.","PeriodicalId":49527,"journal":{"name":"SIAM Journal on Numerical Analysis","volume":"54 1","pages":"2051-2078"},"PeriodicalIF":2.9,"publicationDate":"2026-09-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"149021147","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":"Convergence of Explicit Runge–Kutta Discontinuous Galerkin Approximations of the First-Order Form of Maxwell’s Equations with Low Regularity Solutions","authors":"Alexandre Ern, Jean-Luc Guermond","doi":"10.1137/25m1774793","DOIUrl":"https://doi.org/10.1137/25m1774793","url":null,"abstract":"SIAM Journal on Numerical Analysis, Volume 64, Issue 5, Page 2028-2050, October 2026. <br/> Abstract. We establish a convergence result for the approximation of low-regularity solutions to time-dependent PDE systems that have an involution structure similar to Maxwell’s equations and the linear wave equations. The approximation is based on an explicit Runge–Kutta (ERK) time-stepping and the discontinuous Galerkin (dG) method with stabilization (so-called upwind fluxes) in space. The regularity setting only assumes that the exact solution and its first time derivative are in [math] with a Sobolev regularity index [math] in [math] (here, [math] is the time interval and [math] the space domain), and that its second time derivative is in [math]. The two main tools for the convergence analysis are a Ritz projection in space that leverages recent convergence results in operator norm for the dG approximation of the steady form of the PDE, and the [math]-stability under a standard CFL condition of three-stage, third-order and four-stage, fourth-order ERK schemes. These latter results are known in the literature, but we provide here a somewhat simpler argument to prove the [math]-stability.","PeriodicalId":49527,"journal":{"name":"SIAM Journal on Numerical Analysis","volume":"2 1","pages":"2028-2050"},"PeriodicalIF":2.9,"publicationDate":"2026-09-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"149021148","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":"Monte Carlo Quasi-Interpolation of Spherical Data","authors":"Zhengjie Sun, Mengyuan Lv, Xingping Sun","doi":"10.1137/25m1810490","DOIUrl":"https://doi.org/10.1137/25m1810490","url":null,"abstract":"SIAM Journal on Numerical Analysis, Volume 64, Issue 5, Page 2005-2027, October 2026. <br/> Abstract. We establish a deterministic and stochastic spherical quasi-interpolation framework featuring scaled zonal kernels derived from radial basis functions on the ambient Euclidean space. The method incorporates both quasi–Monte Carlo and Monte Carlo quadrature rules to construct easily computable quasi-interpolants, which provide efficient approximation to Sobolev-space functions for both clean and noisy data. To enhance the approximation power and robustness of our quasi-interpolants, we develop a multilevel method in which quasi-interpolants constructed with graded resolutions join force to reduce the error of approximation. In addition, we derive probabilistic concentration inequalities for our quasi-interpolants in pertinent stochastic settings. The construction of our quasi-interpolants does not require solving any linear system of equations. Numerical experiments show that our quasi-interpolation algorithm is more stable and robust against noise than comparable ones in the literature.","PeriodicalId":49527,"journal":{"name":"SIAM Journal on Numerical Analysis","volume":"22 1","pages":""},"PeriodicalIF":2.9,"publicationDate":"2026-09-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"149009788","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}
Moritz Feuerle, Richard Löscher, Olaf Steinbach, Karsten Urban
{"title":"A Unified Framework for the Analysis, Numerical Approximation, and Model Reduction of Linear Operator Equations, Part I: Well-Posedness in Space and Time","authors":"Moritz Feuerle, Richard Löscher, Olaf Steinbach, Karsten Urban","doi":"10.1137/25m1786040","DOIUrl":"https://doi.org/10.1137/25m1786040","url":null,"abstract":"SIAM Journal on Numerical Analysis, Volume 64, Issue 5, Page 1982-2004, October 2026. <br/> Abstract. We present a unified framework to construct well-posed formulations for large classes of linear operator equations including elliptic, parabolic, and hyperbolic partial differential equations. This general approach incorporates known weak variational formulations as well as novel space-time variational forms of the hyperbolic wave equation. The main concept is completion and extension of operators starting from the strong form of the problem. This paper lays the theoretical foundation for a unified approach toward numerical approximation methods and also model reduction of parameterized linear operator equations which will be the subject of the following parts.","PeriodicalId":49527,"journal":{"name":"SIAM Journal on Numerical Analysis","volume":"269 1","pages":""},"PeriodicalIF":2.9,"publicationDate":"2026-09-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"148985008","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":"Analysis of a Schwarz–Fourier Domain Decomposition Method","authors":"Arnold Reusken","doi":"10.1137/25m1818369","DOIUrl":"https://doi.org/10.1137/25m1818369","url":null,"abstract":"SIAM Journal on Numerical Analysis, Volume 64, Issue 5, Page 1958-1981, October 2026. <br/> Abstract. The Schwarz domain decomposition method can be used for approximately solving a Laplace equation on a domain formed by the union of two overlapping discs. We consider an inexact variant of this method in which the subproblems on the discs are solved approximately using the projection on a Fourier subspace of the [math] space on the boundary. This model problem is relevant for better understanding of the ddCOSMO solver that is used in computational chemistry. We analyze convergence properties of this Schwarz–Fourier domain decomposition method. The analysis is based on maximum principle arguments. We derive a new variant of the maximum principle and contraction number bounds in the maximum norm.","PeriodicalId":49527,"journal":{"name":"SIAM Journal on Numerical Analysis","volume":"39 1","pages":""},"PeriodicalIF":2.9,"publicationDate":"2026-09-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"148922777","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 Convergence Framework for Energy Minimization of Linear Self-Adjoint Elliptic PDEs in Nonlinear Approximation Spaces","authors":"Alexandre Magueresse, Santiago Badia","doi":"10.1137/25m1791470","DOIUrl":"https://doi.org/10.1137/25m1791470","url":null,"abstract":"SIAM Journal on Numerical Analysis, Volume 64, Issue 5, Page 1923-1957, October 2026. <br/> Abstract. Recent years have seen growing interest in solving partial differential equations (PDEs) using nonlinear approximation spaces, where tunable parameters control the basis functions and allow the discretization to adapt dynamically to the solution. While these approaches often perform well in practice, convergence guarantees for the underlying optimization problem remain scarce. This work develops a general optimization framework for energy minimization problems arising from linear self-adjoint elliptic PDEs, formulated over nonlinear approximation spaces admitting a natural split between linear and nonlinear parameters. Linear variables are updated via linear solves or steepest descent, while nonlinear variables are handled using projected gradient descent. We establish local convergence in gradients and in values under modular structural assumptions, including differentiability, boundedness, regularity, and directional convexity, and provide explicit convergence rates in terms of the structural constants of the problem. These assumptions are verified for a broad class of nonlinear approximation spaces, including adaptive finite elements, free-knot splines, kernel methods, and weight-constrained neural networks. Numerical experiments illustrate the benefits of the parameter split and several key aspects of the framework. In a recent work [Magueresse, Badia (2025, arXiv:2508.17705)], we apply the framework to overlapping free-knot tensor-product B-splines, obtaining a geometrically adaptive solver with rigorous convergence guarantees.","PeriodicalId":49527,"journal":{"name":"SIAM Journal on Numerical Analysis","volume":"16 1","pages":""},"PeriodicalIF":2.9,"publicationDate":"2026-09-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"148915612","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}