Andreas Almqvist, Evgeniya Burtseva, Kumbakonam Rajagopal, Peter Wall
{"title":"Modeling pressure-driven flow between adjacent surfaces of viscoplastic and seemingly viscoplastic materials","authors":"Andreas Almqvist, Evgeniya Burtseva, Kumbakonam Rajagopal, Peter Wall","doi":"10.21136/AM.2026.0146-25","DOIUrl":"10.21136/AM.2026.0146-25","url":null,"abstract":"<div><p>A simplified model is derived for pressure-driven flow between adjacent surfaces of materials modeled as seemingly viscoplastic or truly viscoplastic. The material response to external forces is traditionally described by constitutive relations in which the extra stress tensor <b>S</b> is expressed as a function of the symmetric part of the velocity gradient <b>D</b>. However, for viscoplastic materials, <b>S</b> cannot, in general, be written as a function of <b>D</b>, whereas <b>D</b> can be expressed in terms of <b>S</b>. Motivated by this observation, a model based on constitutive relations of the form <b>D</b> = <i>f</i>(<b>S</b>) is proposed, leading to a system of first-order partial differential equations. A local Poiseuille law is also formulated, and a reduced-dimensional equation for the pressure is derived. Explicit velocity profiles are obtained for selected cases.</p></div>","PeriodicalId":55505,"journal":{"name":"Applications of Mathematics","volume":"71 1","pages":"1 - 30"},"PeriodicalIF":0.7,"publicationDate":"2026-01-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://link.springer.com/content/pdf/10.21136/AM.2026.0146-25.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147337863","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"An improved two-step method for inverse singular value problems","authors":"Wei Ma","doi":"10.21136/AM.2026.0096-25","DOIUrl":"10.21136/AM.2026.0096-25","url":null,"abstract":"<div><p>Based on the technique of T. Ogita and K. Aishima (2020) and J. A. Ezquerro and M. A. Hernández (2012), we designed an improved two-step method for solving the inverse singular value problems. Compared with other existing two-step methods, the proposed method has comparable computational cost. However, computing the product of matrices is simpler than solving linear equations and has no instability problem caused by ill-conditioning in solving linear equations, and thus it seems more stable and greatly reducing computational costs. Under appropriate assumptions, the proposed method is proved to be convergent with the cubic root-convergence rate. The proposed method is applied to the noise reduction for modal parameters estimation and indicates that it can significantly remove noise from measured signals and accurately estimate the modal frequencies and damping ratios. The numerical results demonstrate the effectiveness of the improved method.</p></div>","PeriodicalId":55505,"journal":{"name":"Applications of Mathematics","volume":"71 1","pages":"59 - 88"},"PeriodicalIF":0.7,"publicationDate":"2026-01-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147337807","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"Efficient Karhunen-Loève expansions via Legendre-Galerkin discretization and tensor structure","authors":"Michal Béreš","doi":"10.21136/AM.2025.0163-25","DOIUrl":"10.21136/AM.2025.0163-25","url":null,"abstract":"<div><p>We develop an efficient framework for Karhunen-Loève expansions of isotropic Gaussian random fields on hyper-rectangular domains. The approach approximates the co-variance kernel by a positive mixture of squared-exponentials, fitted via Newton optimization with a theoretically informed initialization; we also provide convergence estimates for this Gaussian-mixture approximation. The resulting separable kernel enables a Legendre-Galerkin discretization with a Kronecker product structure across dimensions, together with submatrices exhibiting even/odd parity. For assembly, we employ a Duffy-type transformation followed by Gaussian quadrature. These structural properties substantially reduce memory usage and arithmetic cost compared with naive formulations. All algorithms and numerical experiments are released in an open-source repository that reproduces every figure and table. For completeness, a concise derivation of the three-term recurrence for Legendre polynomials is included in appendix.</p></div>","PeriodicalId":55505,"journal":{"name":"Applications of Mathematics","volume":"70 6","pages":"941 - 991"},"PeriodicalIF":0.7,"publicationDate":"2025-12-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145754428","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"The least squares solution of inconsistent discretized elliptic problems using the FETI method","authors":"Zdeněk Dostál, David Horák","doi":"10.21136/AM.2025.0189-25","DOIUrl":"10.21136/AM.2025.0189-25","url":null,"abstract":"<div><p>The variants of FETI (finite element tearing and interconnecting) based domain decomposition methods are well-established, massively parallel algorithms for solving huge linear systems arising from the discretization of elliptic partial differential equations. Here, we adapt the FETI method for solving the large least squares problems associated with inconsistent systems of linear equations arising from the discretization of elliptic partial differential equations. We briefly review the symmetric least squares problems and the FETI method, explain how FETI can find the least squares solution, prove the optimal rate of convergence, and present the results of numerical experiments demonstrating the efficiency of the proposed method in solving the least squares problem defined by the Poisson equation with inconsistent Neumann conditions.</p></div>","PeriodicalId":55505,"journal":{"name":"Applications of Mathematics","volume":"70 6","pages":"929 - 939"},"PeriodicalIF":0.7,"publicationDate":"2025-12-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145754367","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"Memories of Professor Radim Blaheta","authors":"Stanislav Sysala","doi":"10.21136/AM.2025.0246-25","DOIUrl":"10.21136/AM.2025.0246-25","url":null,"abstract":"<div><p>This special issue is a nice opportunity to honor Professor Radim Blaheta, a well-known Czech numerical mathematician. It was supported by his former collaborators, colleagues, friends, and students. Some of them have also contributed to this issue.</p></div>","PeriodicalId":55505,"journal":{"name":"Applications of Mathematics","volume":"70 6","pages":"729 - 733"},"PeriodicalIF":0.7,"publicationDate":"2025-12-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145754255","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Wietse M. Boon, Johannes Kraus, Tomáš Luber, Maria Lymbery
{"title":"Fitted norm preconditioners for the Hodge-Laplacian in mixed form","authors":"Wietse M. Boon, Johannes Kraus, Tomáš Luber, Maria Lymbery","doi":"10.21136/AM.2025.0185-25","DOIUrl":"10.21136/AM.2025.0185-25","url":null,"abstract":"<div><p>We use the practical framework for abstract perturbed saddle-point problems recently introduced by Hong et al. to analyze the mixed formulation of the Hodge-Laplace problem on a Hilbert complex. We compose two parameter-dependent norms in which the uniform continuity and stability of the problem follow. This not only guarantees the well-posedness of the corresponding variational formulation on the continuous level, but also of related compatible discrete models.</p><p>We further simplify the obtained norms and, in both cases, arrive at the same norm-equivalent preconditioner that is easily implementable. The efficiency and uniformity of the preconditioner are demonstrated numerically by the fast convergence and uniformly bounded number of preconditioned MinRes iterations required to solve various instances of Hodge-Laplace problems in two and three space dimensions.</p></div>","PeriodicalId":55505,"journal":{"name":"Applications of Mathematics","volume":"70 6","pages":"907 - 927"},"PeriodicalIF":0.7,"publicationDate":"2025-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://link.springer.com/content/pdf/10.21136/AM.2025.0185-25.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145754254","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"An adaptive mesh refinement scheme for hierarchical hybrid grids","authors":"Benjamin Mann, Ulrich Rüde","doi":"10.21136/AM.2025.0186-25","DOIUrl":"10.21136/AM.2025.0186-25","url":null,"abstract":"<div><p>This work introduces an adaptive mesh refinement technique for hierarchical hybrid grids with the goal to reach scalability and maintain excellent performance on massively parallel computer systems. On the block-structured hierarchical hybrid grids, this is accomplished by using classical, unstructured refinement only on the coarsest level of the hierarchy, while keeping the number of structured refinement levels constant over the whole domain. This leads to a compromise, where the excellent performance characteristics of hierarchical hybrid grids can be maintained at the price that the flexibility of generating locally refined meshes is constrained. Furthermore, the mesh adaptivity often relies on a posteriori error estimators or error indicators, which tend to become computationally expensive. Again, with the goal of preserving scalability and performance, a method is proposed that leverages the grid hierarchy and the full multigrid scheme. Utilizing the sequence of approximations on the nested hierarchy of grids permits the computation of a cheap error estimator that is well-suited for large-scale parallel computing. We present the theoretical foundations for both global and local error estimates, and present a rigorous analysis of their effectivity. The proposed method, including the error estimator and the adaptive coarse grid refinement, is implemented in the finite element framework H<span>y</span>T<span>e</span>G. Extensive numerical experiments are conducted to validate the effectiveness, as well as performance and scalability.</p></div>","PeriodicalId":55505,"journal":{"name":"Applications of Mathematics","volume":"70 6","pages":"875 - 905"},"PeriodicalIF":0.7,"publicationDate":"2025-11-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145754500","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Ulrich Langer, Richard Löscher, Olaf Steinbach, Huidong Yang
{"title":"State-based approach to the numerical solution of Dirichlet boundary optimal control problems for the Laplace equation","authors":"Ulrich Langer, Richard Löscher, Olaf Steinbach, Huidong Yang","doi":"10.21136/AM.2025.0166-25","DOIUrl":"10.21136/AM.2025.0166-25","url":null,"abstract":"<div><p>We investigate the Dirichlet boundary control of the Laplace equation, considering the control in <i>H</i><sup>1/2</sup>(<i>∂</i>Ω), which is the natural space for Dirichlet data when the state belongs to <i>H</i><sup>1</sup>(Ω) The cost of the control is measured in the <i>H</i><sup>1/2</sup>(<i>∂</i>Ω) norm that also plays the role of the regularization term. We discuss regularization and finite element error estimates enabling us to derive an optimal relation between the finite element mesh size <i>h</i> and the regularization parameter <i>ϱ</i>, balancing the energy cost for the control and the accuracy of the approximation of the desired state. This relationship is also crucial in designing efficient solvers. We also discuss additional box constraints imposed on the control and the state. Our theoretical findings are complemented by numerical examples, including one example with box constraints.</p></div>","PeriodicalId":55505,"journal":{"name":"Applications of Mathematics","volume":"70 6","pages":"797 - 824"},"PeriodicalIF":0.7,"publicationDate":"2025-11-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145754263","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"Algebraic multilevel preconditioning in spectral fractional diffusion","authors":"Svetozar Margenov","doi":"10.21136/AM.2025.0101-25","DOIUrl":"10.21136/AM.2025.0101-25","url":null,"abstract":"<div><p>The numerical solution of linear systems obtained as a result of discretization of a spectral fractional diffusion problem is studied. The finite element method is applied to the considered boundary value problem. The system matrix is a fractional power of the product of the inverse of the mass matrix and the stiffness matrix. The matrix thus defined is symmetric and positive definite (SPD) with respect to the inner product associated with the mass matrix, but is dense, which is consistent with the nonlocal nature of fractional diffusion. The presented results are in the spirit of the BURA (Best Uniform Rational Approximation) method. BURA reduces numerical solution of the dense linear system to the solution of <i>k</i> systems with sparse SPD diffusion-reaction matrices, where <i>k</i> is the degree of rational approximation. We prove the existence of algebraic multilevel iteration (AMLI) methods for preconditioning such type of emergent matrices that satisfy the conditions for optimal computational complexity. Both multiplicative and additive AMLI preconditioners have been developed, determining the minimum possible degree <i>θ</i> of the hierarchical <i>θ</i>-refinement of the mesh.</p></div>","PeriodicalId":55505,"journal":{"name":"Applications of Mathematics","volume":"70 6","pages":"851 - 874"},"PeriodicalIF":0.7,"publicationDate":"2025-11-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145754342","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Daniele Moretto, Andrea Franceschini, Massimiliano Ferronato
{"title":"A stabilized formulation for the mortar method with non-linear contact constraints","authors":"Daniele Moretto, Andrea Franceschini, Massimiliano Ferronato","doi":"10.21136/AM.2025.0149-25","DOIUrl":"10.21136/AM.2025.0149-25","url":null,"abstract":"<div><p>The mortar method is a powerful technique to enforce constraints between non-conforming discretizations by introducing a set of Lagrange multipliers on the connecting interface. Usually, the multipliers are not obtained explicitly because they can be eliminated with the aid of the so-called mortar interpolation operator. However, their explicit computation becomes essential when the contact constraint is governed by some non-linear law, and in this situation it is necessary to guarantee that discrete spaces of the primary variables and multipliers are inf-sup stable. In this work, we investigate the issue of inf-sup stability when using various families of piecewise linear and piecewise constant multipliers. The focus is on the role of the mesh resolution and the enforcement of boundary conditions, which are important factors in practical applications. Then, we develop a stabilized formulation for piecewise-constant multipliers inspired by the framework of minimal stabilization. The effectiveness of the proposed approach is demonstrated through numerical benchmarks and examples.</p></div>","PeriodicalId":55505,"journal":{"name":"Applications of Mathematics","volume":"70 6","pages":"825 - 849"},"PeriodicalIF":0.7,"publicationDate":"2025-11-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://link.springer.com/content/pdf/10.21136/AM.2025.0149-25.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145754315","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}