C. Caballero-Cárdenas , M.J. Castro , C. Chalons , T. Morales de Luna , M.L. Muñoz-Ruiz
{"title":"Semi-implicit fully exactly well-balanced schemes for the two-layer shallow water system","authors":"C. Caballero-Cárdenas , M.J. Castro , C. Chalons , T. Morales de Luna , M.L. Muñoz-Ruiz","doi":"10.1016/j.apnum.2025.07.014","DOIUrl":"10.1016/j.apnum.2025.07.014","url":null,"abstract":"<div><div>This work addresses the design of semi-implicit numerical schemes that are fully exactly well-balanced for the two-layer shallow water system, meaning that they are capable of preserving every possible steady state, and not only the lake-at-rest ones. The proposed approach exhibits better performance compared to standard explicit methods in low-Froude number regimes, where wave propagation speeds significantly exceed flow velocities, thereby reducing the computational cost associated with long-time simulations. The methodology relies on a combination of splitting strategies and relaxation techniques to construct first- and second-order semi-implicit schemes that satisfy the fully exactly well-balanced property.</div></div>","PeriodicalId":8199,"journal":{"name":"Applied Numerical Mathematics","volume":"218 ","pages":"Pages 128-147"},"PeriodicalIF":2.4,"publicationDate":"2025-07-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144720945","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 fast Fourier-Galerkin method for solving boundary integral equations on non-axisymmetric toroidal surfaces","authors":"Yiying Fang , Ying Jiang , Jiafeng Su","doi":"10.1016/j.apnum.2025.07.013","DOIUrl":"10.1016/j.apnum.2025.07.013","url":null,"abstract":"<div><div>We propose a fast Fourier–Galerkin method for solving boundary integral equations (BIEs) on smooth, non-axisymmetric toroidal surfaces. Our approach begins by analyzing the structure of the integral kernel, revealing an exponential decay pattern in the Fourier coefficients after a shear transformation. Leveraging this decay, we design a truncation strategy that compresses the dense representation matrix into a sparse form with only <span><math><mi>O</mi><mo>(</mo><mi>N</mi><msup><mrow><mi>ln</mi></mrow><mrow><mn>2</mn></mrow></msup><mo></mo><mi>N</mi><mo>)</mo></math></span> nonzero entries, where <em>N</em> denotes the degrees of freedom. We rigorously prove that the truncated system retains the stability of the original Fourier–Galerkin formulation and achieves a quasi-optimal convergence rate of <span><math><mi>O</mi><mo>(</mo><msup><mrow><mi>N</mi></mrow><mrow><mo>−</mo><mi>p</mi><mo>/</mo><mn>2</mn></mrow></msup><mi>ln</mi><mo></mo><mi>N</mi><mo>)</mo></math></span>, with <em>p</em> denoting the regularity of the exact solution. Numerical experiments corroborate our theoretical results, demonstrating both high accuracy and computational efficiency. Furthermore, we extend the proposed strategy to BIEs defined on surfaces diffeomorphic to the sphere, confirming the sparsity structure remains exploitable under broader geometric settings.</div></div>","PeriodicalId":8199,"journal":{"name":"Applied Numerical Mathematics","volume":"218 ","pages":"Pages 73-90"},"PeriodicalIF":2.4,"publicationDate":"2025-07-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144720943","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}
Andrés Arrarás , Francisco J. Gaspar , Iñigo Jimenez-Ciga , Laura Portero
{"title":"Space-time parallel solvers for reaction-diffusion problems forming Turing patterns","authors":"Andrés Arrarás , Francisco J. Gaspar , Iñigo Jimenez-Ciga , Laura Portero","doi":"10.1016/j.apnum.2025.07.012","DOIUrl":"10.1016/j.apnum.2025.07.012","url":null,"abstract":"<div><div>In recent years, parallelization has become a strong tool to avoid the limits of classical sequential computing. In the present paper, we introduce four space-time parallel methods that combine the parareal algorithm with suitable splitting techniques for the numerical solution of reaction-diffusion problems. In particular, we consider a suitable partition of the elliptic operator that enables the parallelization in space by using splitting time integrators. Those schemes are then chosen as the propagators of the parareal algorithm, a well-known parallel-in-time method. Both first- and second-order time integrators are considered for this task. The resulting space-time parallel methods are applied to integrate reaction-diffusion problems that model Turing pattern formation. This phenomenon appears in chemical reactions due to diffusion-driven instabilities, and rules the pattern formation for animal coat markings. Such reaction-diffusion problems require fine space and time meshes for their numerical integration, so we illustrate the usefulness of the proposed methods by solving several models of practical interest.</div></div>","PeriodicalId":8199,"journal":{"name":"Applied Numerical Mathematics","volume":"218 ","pages":"Pages 91-108"},"PeriodicalIF":2.4,"publicationDate":"2025-07-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144720946","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":"Robust globally divergence-free weak Galerkin variational data assimilation method for convection-dominated Oseen equations","authors":"Xian Zhang, Ya Min, Minfu Feng","doi":"10.1016/j.apnum.2025.07.011","DOIUrl":"10.1016/j.apnum.2025.07.011","url":null,"abstract":"<div><div>This paper presents a weak Galerkin (WG) finite element method based on the variational approach for data assimilation of the unsteady convection-dominated Oseen equation. The WG scheme uses piecewise polynomials of degrees <em>k</em>(<span><math><mi>k</mi><mo>≥</mo><mn>1</mn></math></span>) and <span><math><mi>k</mi><mo>−</mo><mn>1</mn></math></span> respectively for the approximations of the velocity and the pressure in the interior of elements, and uses piecewise polynomials of degree <em>k</em> for their numerical traces on the interfaces of elements. The method is shown to yield globally divergence-free approximations of the velocity and initial value. It is proved that the velocity error in the <span><math><msup><mrow><mi>L</mi></mrow><mrow><mn>2</mn></mrow></msup></math></span>-norm has a Reynolds-robust error bound with quasi-optimal convergence order <span><math><mi>k</mi><mo>+</mo><mn>1</mn><mo>/</mo><mn>2</mn></math></span> in the convection-dominated region. To solve the discrete optimality system efficiently, the conjugate gradient iterative algorithm is developed, which also preserves the globally divergence-free property of WG scheme. Numerical experiments are provided to verify the obtained theoretical results.</div></div>","PeriodicalId":8199,"journal":{"name":"Applied Numerical Mathematics","volume":"218 ","pages":"Pages 22-42"},"PeriodicalIF":2.2,"publicationDate":"2025-07-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144686025","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":"H(div)-conforming IPDG FEM with pointwise divergence-free velocity field for the micropolar Navier-Stokes equations","authors":"Xinran Huang, Haiyan Su, Xinlong Feng","doi":"10.1016/j.apnum.2025.07.007","DOIUrl":"10.1016/j.apnum.2025.07.007","url":null,"abstract":"<div><div>The mass-conservative finite element method (FEM) is considered for the micropolar Navier-Stokes equations (MNSE), which couple the Navier-Stokes equations (NSE) with the angular momentum equation. A fully divergence-free algorithm is proposed for the MNSE. The Raviart-Thomas element is employed for discretizing the velocity field, ensuring that its divergence-free property is maintained. Furthermore, the interior penalty discontinuous Galerkin (IPDG) method is utilized in order to guarantee the <span><math><msup><mrow><mi>H</mi></mrow><mrow><mn>1</mn></mrow></msup></math></span>-continuity of velocity. Some implicit-explicit treatments are used to address the convection terms. We also provide energy stability proof and pressure robust error estimation for the proposed scheme. Finally, the accuracy and effectiveness of the proposed algorithm are validated through several 2D/3D numerical experiments.</div></div>","PeriodicalId":8199,"journal":{"name":"Applied Numerical Mathematics","volume":"218 ","pages":"Pages 109-127"},"PeriodicalIF":2.4,"publicationDate":"2025-07-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144720944","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 novel amplifying methodology in Gauss-Legendre IRK integrations to cope with high-frequency stiff problems","authors":"Sanaz Hami Hassan Kiyadeh , Hosein Saadat , Ramin Goudarzi Karim , Ali Safaie , Fayyaz Khodadosti","doi":"10.1016/j.apnum.2025.07.006","DOIUrl":"10.1016/j.apnum.2025.07.006","url":null,"abstract":"<div><div>This work presents a new amplification methodology based on the widely used Gauss-Legendre implicit Runge-Kutta integrations by addressing the phase lag and amplification factor. The novel methodology focuses on these two elements, which are the complex amplifiers associated with the GLIRK integrations.</div><div>To enhance the amplifier capabilities of the GLIRK integrations, we introduce two novel equations that clarify the relationships between the amplification factor and phase lag. This paper culminates in the improvement of two well-defined GLIRK integrations, each carefully designed to eliminate both the phase lag and the amplification factor in practical applications. The examination of absolute stability regions in the complex plane, as well as stability regions in the <em>z</em>-<em>v</em> plane, is relevant to the new GLIRK integrations presented.</div><div>To satisfy the admissibility of the new methodology, we establish a competitive environment alongside the classical GLIRK integration.</div><div>This competitive space includes numerical examples that demonstrate the low cost of the new amplified GLIRK integrations in addressing stiff problems with high frequency. Ultimately, this cost-effectiveness and superiority become increasingly evident as the frequency of the stiff problems increases.</div></div>","PeriodicalId":8199,"journal":{"name":"Applied Numerical Mathematics","volume":"218 ","pages":"Pages 43-57"},"PeriodicalIF":2.2,"publicationDate":"2025-07-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144694462","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}
Kwanghyuk Park , Xinjuan Chen , Dongjin Lee , Jiaxi Gu , Jae-Hun Jung
{"title":"A third-order finite difference weighted essentially non-oscillatory scheme with shallow neural network","authors":"Kwanghyuk Park , Xinjuan Chen , Dongjin Lee , Jiaxi Gu , Jae-Hun Jung","doi":"10.1016/j.apnum.2025.07.005","DOIUrl":"10.1016/j.apnum.2025.07.005","url":null,"abstract":"<div><div>In this work, we develop the finite difference weighted essentially non-oscillatory (WENO) scheme based on the neural network for hyperbolic conservation laws. Supervised learning is employed with the training data consisting of three-point stencils and the corresponding WENO3-JS weights as labels. We design two loss functions, one built on the mean squared error and the other from the mean squared logarithmic error. Each loss function consists of two components, where the first enforces the model to maintain the essentially non-oscillatory behavior while the second reduces the dissipation around discontinuities and improves the performance in smooth regions. We choose the shallow neural network (SNN) for computational efficiency with the Delta layer pre-processing the input. The resulting WENO3-SNN schemes outperform the classical WENO3-JS and WENO3-Z in one-dimensional examples, and show comparable sometimes superior simulations to WENO3-JS and WENO3-Z in two-dimensional examples.</div></div>","PeriodicalId":8199,"journal":{"name":"Applied Numerical Mathematics","volume":"218 ","pages":"Pages 1-21"},"PeriodicalIF":2.2,"publicationDate":"2025-07-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144656379","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 a two-grid BDF2 virtual element scheme for semilinear parabolic equation","authors":"Peixuan Wu, Xiaohui Wu, Yang Wang, Ruqing Wang","doi":"10.1016/j.apnum.2025.07.002","DOIUrl":"10.1016/j.apnum.2025.07.002","url":null,"abstract":"<div><div>In this article, we present a new two-grid discretization for the approximation of semilinear parabolic equation found on virtual element method (VEM). The two-step backward differentiation formula (BDF2) is comtemplated in the time dimension, while the VEM is utilized in spatial dimension. The two-grid VEM primarily computes the numerical solution <span><math><msubsup><mrow><mi>W</mi></mrow><mrow><mi>H</mi></mrow><mrow><mi>n</mi></mrow></msubsup></math></span> from solving a nonlinear system on a coarse mesh with size <em>H</em> and then gets the numerical solution <span><math><msubsup><mrow><mi>W</mi></mrow><mrow><mi>h</mi></mrow><mrow><mi>n</mi></mrow></msubsup></math></span> to a linear system built by the earlier result <span><math><msubsup><mrow><mi>W</mi></mrow><mrow><mi>H</mi></mrow><mrow><mi>n</mi></mrow></msubsup></math></span> on a fine mesh with size <em>h</em> (<span><math><mi>h</mi><mo>≪</mo><mi>H</mi></math></span>). Consequently, our proposed scheme not only reduces total computational expense, but also achieves same accuracy as the single-grid VEM. The convergence analysis in <span><math><msup><mrow><mi>L</mi></mrow><mrow><mn>2</mn></mrow></msup></math></span> and semi-<span><math><msup><mrow><mi>H</mi></mrow><mrow><mn>1</mn></mrow></msup></math></span> norm for both the VEM and the two-grid VEM methods are provided concretely.</div></div>","PeriodicalId":8199,"journal":{"name":"Applied Numerical Mathematics","volume":"217 ","pages":"Pages 451-475"},"PeriodicalIF":2.2,"publicationDate":"2025-07-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144631126","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 linear-decoupled and unconditionally energy stable fully discrete scheme for Peterlin viscoelastic model","authors":"Qi Wang , Kun Wang , Guanyu Zhou","doi":"10.1016/j.apnum.2025.07.001","DOIUrl":"10.1016/j.apnum.2025.07.001","url":null,"abstract":"<div><div>In this paper, we design a linear-decoupled and unconditionally energy stable scheme utilizing the ZEC (“zero-energy-contribution”) technique for the diffusion Peterlin viscoelastic model. This model includes a diffusion term with an arbitrary small diffusion coefficient <em>ε</em> for the conformation tensor <strong><em>C</em></strong>. A specific ODE is introduced to deal with the nonlinear coupling terms for velocity <strong><em>u</em></strong> and <strong><em>C</em></strong> satisfying the ZEC property. We approximate the coupled nonlinear terms using the previous time-step results while still maintaining energy stability, allowing us to solve a linear-decoupled system at each time-step. Moreover, each component of <strong><em>C</em></strong> can be computed in parallel. We prove the unique solvability and energy stability of the fully discrete scheme. Additionally, we derive an error bound <span><math><mi>C</mi><mo>(</mo><mi>τ</mi><mo>+</mo><msup><mrow><mi>h</mi></mrow><mrow><mn>2</mn></mrow></msup><mo>)</mo></math></span> for the P2/P1/P2 element, where the constant <span><math><mi>C</mi></math></span> is not explicitly dependent on the reciprocal of <em>ε</em>. Several numerical experiments are presented to demonstrate the accuracy and performance of the proposed scheme. Comparison with a linear-decoupled scheme excluding the ZEC technique indicates that the proposed algorithm offers superior stability and performance.</div></div>","PeriodicalId":8199,"journal":{"name":"Applied Numerical Mathematics","volume":"217 ","pages":"Pages 412-435"},"PeriodicalIF":2.2,"publicationDate":"2025-07-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144597209","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 higher-order solver for the FitzHugh-Nagumo equation by combining nonstandard and compact finite difference scheme","authors":"Zhi-Chen Li , Yang-Wen Yu , Xiao-Yu Zhang , Qing Fang","doi":"10.1016/j.apnum.2025.07.004","DOIUrl":"10.1016/j.apnum.2025.07.004","url":null,"abstract":"<div><div>This study presents a novel numerical method for solving the FitzHugh-Nagumo equation by combining nonstandard finite difference (NSFD) and high-order compact finite difference schemes. Through rigorous mathematical analysis, we demonstrate the stability and convergence of our approach, revealing that instability arises only under extremely rare conditions. To verify the efficiency of our scheme, we calculated the <span><math><msub><mrow><mi>l</mi></mrow><mrow><mn>2</mn></mrow></msub></math></span> and <span><math><msub><mrow><mi>l</mi></mrow><mrow><mo>∞</mo></mrow></msub></math></span> errors as well as the convergence rate by comparing the numerical results with the exact solution. Experiments show that our combined scheme not only ensures stability, but also possesses the lowest error while maintaining high order convergence.</div></div>","PeriodicalId":8199,"journal":{"name":"Applied Numerical Mathematics","volume":"217 ","pages":"Pages 436-450"},"PeriodicalIF":2.2,"publicationDate":"2025-07-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144614256","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}