Linear Algebra and its Applications最新文献

{"title":"Extensions on spectral extrema of θ1,2,5-free graphs with given size","authors":"Chang Liu,&nbsp;Jianping Li","doi":"10.1016/j.laa.2025.04.010","DOIUrl":"10.1016/j.laa.2025.04.010","url":null,"abstract":"<div><div>The Brualdi-Hoffman-Turán type problem is an important category of spectral Turán problems, focusing on determining the maximum spectral radius of an <span><math><mi>F</mi></math></span>-free graph with <em>m</em> edges. This topic has received considerable attention in recent years. Let <span><math><mi>G</mi><mo>(</mo><mi>m</mi><mo>,</mo><mi>F</mi><mo>)</mo></math></span> denote the set of <span><math><mi>F</mi></math></span>-free graphs with <em>m</em> edges and no isolated vertices. Define <span><math><msub><mrow><mi>θ</mi></mrow><mrow><mi>p</mi><mo>,</mo><mi>q</mi><mo>,</mo><mi>r</mi></mrow></msub></math></span> as the theta graph, consisting of three internally disjoint paths of lengths <em>p</em>, <em>q</em>, and <em>r</em>, sharing the same pair of endpoints. Recently, Lu et al. (2024) <span><span>[16]</span></span> determined that the unique extremal graph with the maximum spectral radius in <span><math><mi>G</mi><mo>(</mo><mi>m</mi><mo>,</mo><msub><mrow><mi>θ</mi></mrow><mrow><mn>1</mn><mo>,</mo><mn>2</mn><mo>,</mo><mn>5</mn></mrow></msub><mo>)</mo></math></span> is <span><math><msub><mrow><mi>S</mi></mrow><mrow><mfrac><mrow><mi>m</mi><mo>+</mo><mn>6</mn></mrow><mrow><mn>3</mn></mrow></mfrac><mo>,</mo><mn>3</mn></mrow></msub></math></span> for <span><math><mi>m</mi><mo>≥</mo><mn>38</mn></math></span>. However, the extremal graph is well-defined only when <span><math><mi>m</mi><mo>≡</mo><mn>0</mn><mspace></mspace><mo>(</mo><mrow><mi>mod</mi></mrow><mspace></mspace><mn>3</mn><mo>)</mo></math></span>. In this paper, we employ a new technique to characterize the graphs with the maximum spectral radius among all <span><math><msub><mrow><mi>θ</mi></mrow><mrow><mn>1</mn><mo>,</mo><mn>2</mn><mo>,</mo><mn>5</mn></mrow></msub></math></span>-free graphs for <span><math><mi>m</mi><mo>≥</mo><mn>39</mn></math></span>, where <span><math><mi>m</mi><mo>≡</mo><mn>1</mn><mspace></mspace><mo>(</mo><mrow><mi>mod</mi></mrow><mspace></mspace><mn>3</mn><mo>)</mo></math></span> or <span><math><mi>m</mi><mo>≡</mo><mn>2</mn><mspace></mspace><mo>(</mo><mrow><mi>mod</mi></mrow><mspace></mspace><mn>3</mn><mo>)</mo></math></span>. Finally, we propose two conjectures that generalize Zhai et al. (2021) <span><span>[31]</span></span>.</div></div>","PeriodicalId":18043,"journal":{"name":"Linear Algebra and its Applications","volume":"719 ","pages":"Pages 136-157"},"PeriodicalIF":1.0,"publicationDate":"2025-04-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143886056","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Complete characterization of symmetric Kubo-Ando operator means satisfying Molnár's weak associativity","authors":"Yury Grabovsky ,&nbsp;Graeme W. Milton ,&nbsp;Aaron Welters","doi":"10.1016/j.laa.2025.04.015","DOIUrl":"10.1016/j.laa.2025.04.015","url":null,"abstract":"<div><div>We provide a complete characterization of a subclass of weakly associative means of positive operators in the class of symmetric Kubo-Ando means. This class, which includes the geometric mean, was first introduced and studied in Molnár (2019) <span><span>[24]</span></span>, where he gives a characterization of this subclass (which we call the Molnár class of means) in terms of the properties of their representing operator monotone functions. Molnár's paper leaves open the problem of determining if the geometric mean is the only such mean in that subclass. Here we give a negative answer to this question by constructing an order-preserving bijection between this class and a class of real measurable odd periodic functions bounded in absolute value by 1/2. Each member of the latter class defines a Molnár mean by an explicit exponential-integral representation. From this we are able to understand the order structure of the Molnár class and construct several infinite families of explicit examples of Molnár means that are not the geometric mean. Our analysis also shows how to modify Molnár's original characterization so that the geometric mean is the only one satisfying the requisite set of properties.</div></div>","PeriodicalId":18043,"journal":{"name":"Linear Algebra and its Applications","volume":"719 ","pages":"Pages 158-182"},"PeriodicalIF":1.0,"publicationDate":"2025-04-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143894761","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Partial classification of spectrum maximizing products for pairs of 2 × 2 matrices","authors":"Piotr Laskawiec","doi":"10.1016/j.laa.2025.04.014","DOIUrl":"10.1016/j.laa.2025.04.014","url":null,"abstract":"<div><div>Experiments suggest that typical finite sets of square matrices admit spectrum maximizing products (SMPs): that is, products that attain the joint spectral radius (JSR). Furthermore, those SMPs are often combinatorially “simple.” In this paper, we consider pairs of real <span><math><mn>2</mn><mo>×</mo><mn>2</mn></math></span> matrices. We identify regions in the space of such pairs where SMPs are guaranteed to exist and to have a simple structure. We also identify another region where SMPs may fail to exist (in fact, this region includes all known counterexamples to the finiteness conjecture), but nevertheless a Sturmian maximizing measure exists. Though our results apply to a large chunk of the space of pairs of <span><math><mn>2</mn><mo>×</mo><mn>2</mn></math></span> matrices, including for instance all pairs of non-negative matrices, they leave out certain “wild” regions where more complicated behavior is possible.</div></div>","PeriodicalId":18043,"journal":{"name":"Linear Algebra and its Applications","volume":"719 ","pages":"Pages 103-135"},"PeriodicalIF":1.0,"publicationDate":"2025-04-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143886055","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Maximization of the first Laplace eigenvalue of a finite graph","authors":"Takumi Gomyou ,&nbsp;Shin Nayatani","doi":"10.1016/j.laa.2025.04.013","DOIUrl":"10.1016/j.laa.2025.04.013","url":null,"abstract":"<div><div>Given a length function on the edge set of a finite graph, we define a vertex-weight and an edge-weight in terms of it and consider the corresponding graph Laplacian. In this paper, we consider the problem of maximizing the first nonzero eigenvalue of this Laplacian over all edge-length functions subject to a certain normalization. For an extremal solution of this problem, we prove that there exists a map from the vertex set to a Euclidean space consisting of first eigenfunctions of the corresponding Laplacian so that the length function can be explicitly expressed in terms of the map and the Euclidean distance. This is a graph-analogue of Nadirashvili's result related to first-eigenvalue maximization problem on a smooth surface. We discuss simple examples and also prove a similar result for a maximizing solution of the Göring-Helmberg-Wappler problem.</div></div>","PeriodicalId":18043,"journal":{"name":"Linear Algebra and its Applications","volume":"720 ","pages":"Pages 72-90"},"PeriodicalIF":1.0,"publicationDate":"2025-04-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143912831","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Irreducible actions of finite hypergroups and association schemes","authors":"Gang Chen ,&nbsp;Bangteng Xu","doi":"10.1016/j.laa.2025.04.012","DOIUrl":"10.1016/j.laa.2025.04.012","url":null,"abstract":"<div><div>The action of a finite hypergroup, introduced by Sunder and Wildberger <span><span>[14]</span></span>, is an important tool in the study of finite hypergroups. It is defined via column-stochastic matrices. Finite hypergroups have close connections to association schemes. Actions of finite hypergroups have been used to construct association schemes in Sunder and Wildberger <span><span>[14]</span></span> and Xu <span><span>[22]</span></span>. In this paper, we study the characterizations of irreducible actions of finite hypergroups and investigate the constructions of association schemes arising from these irreducible actions. We will first obtain the characterizations of irreducible actions of finite hypergroups through the irreducibility of certain stochastic matrices. Then we establish some sufficient and necessary conditions under which an irreducible action of a finite hypergroup gives rise to an association scheme.</div></div>","PeriodicalId":18043,"journal":{"name":"Linear Algebra and its Applications","volume":"720 ","pages":"Pages 26-49"},"PeriodicalIF":1.0,"publicationDate":"2025-04-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143888267","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Projections onto polyhedral sets: An improved finite step method and new distributed projection methods","authors":"Yongchao Yu ,&nbsp;Chongyang Wang","doi":"10.1016/j.laa.2025.04.009","DOIUrl":"10.1016/j.laa.2025.04.009","url":null,"abstract":"<div><div>A polyhedral set is the intersection of a finite number of closed half-spaces. It is very difficult to obtain the projection of any point onto a general polyhedral set, especially when the polyhedral set is formed by a large number of closed half-spaces. In this work, we focus on the theoretical aspects of the projection problem itself and of related methods for solving it. The first part of this work is to systematically study various optimality conditions on the projection problem by using the projection theorem. The second part of this work is to design a safe and verifiable screening rule to improve the computational efficiency of Rutkowski's finite step method. In the third part of this work, we introduce a graph-based parameterized operator and prove its conical averagedness. We then propose the convergent scheme of the Krasnosel'skiĭ–Mann fixed point iteration of this operator to find the projection. We also point out that, if we take incidence matrices of graphs as decomposition matrices in the graph-based scheme, the scheme has satisfactory distributability. Several special connected graph networks are provided and under their guidance, new explicit distributed projection methods are shown. These graph-based distributed schemes and methods are also extended to solve the problem of projecting onto finitely generated cones.</div></div>","PeriodicalId":18043,"journal":{"name":"Linear Algebra and its Applications","volume":"719 ","pages":"Pages 34-65"},"PeriodicalIF":1.0,"publicationDate":"2025-04-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143870527","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Convergence of complementable operators","authors":"Sachin Manjunath Naik,&nbsp;P. Sam Johnson","doi":"10.1016/j.laa.2025.04.008","DOIUrl":"10.1016/j.laa.2025.04.008","url":null,"abstract":"<div><div>Complementable operators extend classical matrix decompositions, such as the Schur complement, to the setting of infinite-dimensional Hilbert spaces, thereby broadening their applicability in various mathematical and physical contexts. This paper focuses on the convergence properties of complementable operators, investigating when the limit of sequence of complementable operators remains complementable. We also explore the convergence of sequences and series of powers of complementable operators, providing new insights into their convergence behavior. Additionally, we examine the conditions under which the set of complementable operators is the subset of set of boundary points of the set of non-complementable operators with respect to the strong operator topology. The paper further explores the topological structure of the subset of complementable operators, offering a characterization of its closed subsets.</div></div>","PeriodicalId":18043,"journal":{"name":"Linear Algebra and its Applications","volume":"719 ","pages":"Pages 66-92"},"PeriodicalIF":1.0,"publicationDate":"2025-04-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143870528","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Counting core sets in matrix rings over finite fields","authors":"Roswitha Rissner ,&nbsp;Nicholas J. Werner","doi":"10.1016/j.laa.2025.04.006","DOIUrl":"10.1016/j.laa.2025.04.006","url":null,"abstract":"<div><div>Let <em>R</em> be a commutative ring and <span><math><msub><mrow><mi>M</mi></mrow><mrow><mi>n</mi></mrow></msub><mo>(</mo><mi>R</mi><mo>)</mo></math></span> be the ring of <span><math><mi>n</mi><mo>×</mo><mi>n</mi></math></span> matrices with entries from <em>R</em>. For each <span><math><mi>S</mi><mo>⊆</mo><msub><mrow><mi>M</mi></mrow><mrow><mi>n</mi></mrow></msub><mo>(</mo><mi>R</mi><mo>)</mo></math></span>, we consider its (generalized) null ideal <span><math><mi>N</mi><mo>(</mo><mi>S</mi><mo>)</mo></math></span>, which is the set of all polynomials <em>f</em> with coefficients from <span><math><msub><mrow><mi>M</mi></mrow><mrow><mi>n</mi></mrow></msub><mo>(</mo><mi>R</mi><mo>)</mo></math></span> with the property that <span><math><mi>f</mi><mo>(</mo><mi>A</mi><mo>)</mo><mo>=</mo><mn>0</mn></math></span> for all <span><math><mi>A</mi><mo>∈</mo><mi>S</mi></math></span>. The set <em>S</em> is said to be core if <span><math><mi>N</mi><mo>(</mo><mi>S</mi><mo>)</mo></math></span> is a two-sided ideal of <span><math><msub><mrow><mi>M</mi></mrow><mrow><mi>n</mi></mrow></msub><mo>(</mo><mi>R</mi><mo>)</mo><mo>[</mo><mi>x</mi><mo>]</mo></math></span>. It is not known how common core sets are among all subsets of <span><math><msub><mrow><mi>M</mi></mrow><mrow><mi>n</mi></mrow></msub><mo>(</mo><mi>R</mi><mo>)</mo></math></span>. We study this problem for <span><math><mn>2</mn><mo>×</mo><mn>2</mn></math></span> matrices over <span><math><msub><mrow><mi>F</mi></mrow><mrow><mi>q</mi></mrow></msub></math></span>, where <span><math><msub><mrow><mi>F</mi></mrow><mrow><mi>q</mi></mrow></msub></math></span> is the finite field with <em>q</em> elements. We provide exact counts for the number of core subsets of each similarity class of <span><math><msub><mrow><mi>M</mi></mrow><mrow><mn>2</mn></mrow></msub><mo>(</mo><msub><mrow><mi>F</mi></mrow><mrow><mi>q</mi></mrow></msub><mo>)</mo></math></span>. While not every subset of <span><math><msub><mrow><mi>M</mi></mrow><mrow><mn>2</mn></mrow></msub><mo>(</mo><msub><mrow><mi>F</mi></mrow><mrow><mi>q</mi></mrow></msub><mo>)</mo></math></span> is core, we prove that as <span><math><mi>q</mi><mo>→</mo><mo>∞</mo></math></span>, the probability that a subset of <span><math><msub><mrow><mi>M</mi></mrow><mrow><mn>2</mn></mrow></msub><mo>(</mo><msub><mrow><mi>F</mi></mrow><mrow><mi>q</mi></mrow></msub><mo>)</mo></math></span> is core approaches 1. Thus, asymptotically in <em>q</em>, almost all subsets of <span><math><msub><mrow><mi>M</mi></mrow><mrow><mn>2</mn></mrow></msub><mo>(</mo><msub><mrow><mi>F</mi></mrow><mrow><mi>q</mi></mrow></msub><mo>)</mo></math></span> are core.</div></div>","PeriodicalId":18043,"journal":{"name":"Linear Algebra and its Applications","volume":"720 ","pages":"Pages 1-25"},"PeriodicalIF":1.0,"publicationDate":"2025-04-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143869167","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Spectral w-variation of trees in two places","authors":"Parameswar Basumatary ,&nbsp;Debajit Kalita","doi":"10.1016/j.laa.2025.04.003","DOIUrl":"10.1016/j.laa.2025.04.003","url":null,"abstract":"<div><div>This article introduces the concept of spectral <em>w</em>-variation of weighted graphs. A weighted graph <em>G</em> is said to have spectral <em>w</em>-variation in two places if adding an edge of positive weight <em>w</em> between two nonadjacent vertices of <em>G</em>, or increasing the weight of an existing edge by <em>w</em>, results in an increase of two Laplacian eigenvalues of <em>G</em> equally by <em>w</em> while keeping the other eigenvalues unchanged. This article characterizes the weighted graphs that have spectral <em>w</em>-variation in two places. It is proved that spectral <em>w</em>-variation in two places does not occur by increasing the weight of an existing edge in any weighted tree. Mainly, the article determines the weighted trees that have spectral <em>w</em>-variation in two places. As an application, we supply constructions of few classes of weighted trees with weights from the interval <span><math><mo>(</mo><mn>0</mn><mo>,</mo><mn>1</mn><mo>)</mo></math></span> in which spectral <em>w</em>-variation occurs in two places.</div></div>","PeriodicalId":18043,"journal":{"name":"Linear Algebra and its Applications","volume":"718 ","pages":"Pages 81-103"},"PeriodicalIF":1.0,"publicationDate":"2025-04-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143860337","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Periodicity and circulant matrices in the Riordan array of a polynomial","authors":"Nikolai A. Krylov","doi":"10.1016/j.laa.2025.04.005","DOIUrl":"10.1016/j.laa.2025.04.005","url":null,"abstract":"<div><div>We consider Riordan arrays <span><math><mo>(</mo><mn>1</mn><mo>/</mo><mo>(</mo><mn>1</mn><mo>−</mo><msup><mrow><mi>t</mi></mrow><mrow><mi>d</mi><mo>+</mo><mn>1</mn></mrow></msup><mo>)</mo><mo>,</mo><mspace></mspace><mi>t</mi><mi>p</mi><mo>(</mo><mi>t</mi><mo>)</mo><mo>)</mo></math></span>. These are infinite lower triangular matrices determined by the formal power series <span><math><mn>1</mn><mo>/</mo><mo>(</mo><mn>1</mn><mo>−</mo><msup><mrow><mi>t</mi></mrow><mrow><mi>d</mi><mo>+</mo><mn>1</mn></mrow></msup><mo>)</mo></math></span> and a polynomial <span><math><mi>p</mi><mo>(</mo><mi>t</mi><mo>)</mo></math></span> of degree <em>d</em>. Columns of such a matrix are eventually periodic sequences with a period of <span><math><mi>d</mi><mo>+</mo><mn>1</mn></math></span>, and circulant matrices are used to describe the long term behavior of such periodicity when the column's index grows indefinitely. We also discuss some combinatorially interesting sequences that appear through the corresponding A - and Z - sequences of such Riordan arrays.</div></div>","PeriodicalId":18043,"journal":{"name":"Linear Algebra and its Applications","volume":"718 ","pages":"Pages 58-80"},"PeriodicalIF":1.0,"publicationDate":"2025-04-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143834143","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}