{"title":"A generalization of Fiedler's lemma and its applications","authors":"Yangyang Wu, Xiaoling Ma","doi":"10.1016/j.laa.2024.07.008","DOIUrl":"10.1016/j.laa.2024.07.008","url":null,"abstract":"<div><p>In this article, taking a Fiedler's result on the spectrum of a matrix formed from two symmetric matrices as a motivation, we deduce a more general result on the eigenvalues of a matrix, which form from <em>n</em> symmetric matrices. As an important application, we obtain the adjacency spectra, Laplacian spectra and signless Laplacian spectra of a graph with a particular almost equitable partition.</p></div>","PeriodicalId":18043,"journal":{"name":"Linear Algebra and its Applications","volume":null,"pages":null},"PeriodicalIF":1.0,"publicationDate":"2024-07-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141696804","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":"On the invertibility of matrices with a double saddle-point structure","authors":"Fatemeh P.A. Beik , Chen Greif , Manfred Trummer","doi":"10.1016/j.laa.2024.07.005","DOIUrl":"10.1016/j.laa.2024.07.005","url":null,"abstract":"<div><p>We establish necessary and sufficient conditions for invertibility of symmetric three-by-three block matrices having a double saddle-point structure that guarantee the unique solvability of double saddle-point systems. We consider various scenarios, including the case where all diagonal blocks are allowed to be rank deficient. Under certain conditions related to the nullity of the blocks and intersections of their kernels, an explicit formula for the inverse is derived.</p></div>","PeriodicalId":18043,"journal":{"name":"Linear Algebra and its Applications","volume":null,"pages":null},"PeriodicalIF":1.0,"publicationDate":"2024-07-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.sciencedirect.com/science/article/pii/S0024379524002957/pdfft?md5=2f9745e86feef3ccac116a6ac9360448&pid=1-s2.0-S0024379524002957-main.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141720123","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"Anzahl theorems for trivially intersecting subspaces generating a non-singular subspace I: Symplectic and hermitian forms","authors":"Maarten De Boeck , Geertrui Van de Voorde","doi":"10.1016/j.laa.2024.07.004","DOIUrl":"10.1016/j.laa.2024.07.004","url":null,"abstract":"<div><p>In this paper, we solve a classical counting problem for non-degenerate forms of symplectic and hermitian type defined on a vector space: given a subspace <em>π</em>, we find the number of non-singular subspaces that are trivially intersecting with <em>π</em> and span a non-singular subspace with <em>π</em>. Lower bounds for the quantity of such pairs where <em>π</em> is non-singular were first studied in “Glasby, Niemeyer, Praeger (Finite Fields Appl., 2022)”, which was later improved in “Glasby, Ihringer, Mattheus (Des. Codes Cryptogr., 2023)” and generalised in “Glasby, Niemeyer, Praeger (Linear Algebra Appl., 2022)”. In this paper, we derive explicit formulae, which allow us to give the exact proportion and improve the known lower bounds.</p></div>","PeriodicalId":18043,"journal":{"name":"Linear Algebra and its Applications","volume":null,"pages":null},"PeriodicalIF":1.0,"publicationDate":"2024-07-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141694473","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":"Representations of the C-series related to the q-analog Virasoro-like Lie algebra","authors":"","doi":"10.1016/j.laa.2024.06.028","DOIUrl":"10.1016/j.laa.2024.06.028","url":null,"abstract":"<div><p>In this paper, we study the representation of an infinite-dimensional Lie algebra <span><math><mi>C</mi></math></span> related to the q-analog Virasoro-like Lie algebra. We give the necessary and sufficient conditions for the highest weight irreducible module <span><math><mi>V</mi><mo>(</mo><mi>ϕ</mi><mo>)</mo></math></span> of <span><math><mi>C</mi></math></span> to be a Harish-Chandra module. We prove that the Verma <span><math><mi>C</mi></math></span>-module <span><math><mover><mrow><mi>V</mi></mrow><mrow><mo>¯</mo></mrow></mover><mo>(</mo><mi>ϕ</mi><mo>)</mo></math></span> is either irreducible or has the corresponding irreducible highest weight <span><math><mi>C</mi></math></span>-module <span><math><mi>V</mi><mo>(</mo><mi>ϕ</mi><mo>)</mo></math></span> that is a Harish-Chandra module. We also give the maximal proper submodule of the Verma module <span><math><mover><mrow><mi>V</mi></mrow><mrow><mo>¯</mo></mrow></mover><mo>(</mo><mi>ϕ</mi><mo>)</mo></math></span> and the <em>e</em>-character of the irreducible highest weight <span><math><mi>C</mi></math></span>-module <span><math><mi>V</mi><mo>(</mo><mi>ϕ</mi><mo>)</mo></math></span> when the highest weight <em>ϕ</em> satisfies some natural conditions. Furthermore, we give the classification of the Harish-Chandra <span><math><mi>C</mi></math></span>-modules with nontrivial central charge.</p></div>","PeriodicalId":18043,"journal":{"name":"Linear Algebra and its Applications","volume":null,"pages":null},"PeriodicalIF":1.0,"publicationDate":"2024-07-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141588541","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":"A low-rank ODE for spectral clustering stability","authors":"Nicola Guglielmi, Stefano Sicilia","doi":"10.1016/j.laa.2024.07.001","DOIUrl":"https://doi.org/10.1016/j.laa.2024.07.001","url":null,"abstract":"Spectral clustering is a well-known technique which identifies clusters in an undirected graph, with vertices and weight matrix , by exploiting its graph Laplacian . In particular, the clusters can be identified by the knowledge of the eigenvectors associated with the smallest non zero eigenvalues of , say (recall that ). Identifying is an essential task of a clustering algorithm, since if is close to the reliability of the method is reduced. The -th spectral gap is often considered as a stability indicator. This difference can be seen as an unstructured distance between and an arbitrary symmetric matrix with vanishing -th spectral gap. A more appropriate structured distance to ambiguity such that represents the Laplacian of a graph has been proposed in Andreotti et al. (2021) . This is defined as the minimal distance between and Laplacians of graphs with the same vertices and edges, but with weights that are perturbed such that the -th spectral gap vanishes. In this article we consider a slightly different approach, still based on the reformulation of the problem into the minimization of a suitable functional in the eigenvalues. After determining the gradient system associated with this functional, we introduce a low-rank projected system, suggested by the underlying low-rank structure of the extremizers of the problem. The integration of this low-rank system, requires both a moderate computational effort and a memory requirement, as it is shown in some illustrative numerical examples.","PeriodicalId":18043,"journal":{"name":"Linear Algebra and its Applications","volume":null,"pages":null},"PeriodicalIF":1.1,"publicationDate":"2024-07-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141587729","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":"Positive vectors, pairwise comparison matrices and directed Hamiltonian cycles","authors":"","doi":"10.1016/j.laa.2024.07.003","DOIUrl":"10.1016/j.laa.2024.07.003","url":null,"abstract":"<div><p>In the Analytic Hierarchy Process (AHP) the efficient vectors for a pairwise comparison matrix (PC matrix) are based on the principle of Pareto optimal decisions. To infer the efficiency of a vector for a PC matrix we construct a directed Hamiltonian cycle of a certain digraph associated with the PC matrix and the vector. We describe advantages of using this process over using the strong connectivity of the digraph. As an application of our process we find efficient vectors for a PC matrix, A, obtained from a consistent one by perturbing three entries above the main diagonal and the corresponding reciprocal entries, in a way that there is a square submatrix of A of order 2 containing three of the perturbed entries and not containing a diagonal entry of A. For completeness, we include examples showing conditions under which, when deleting a certain entry of an efficient vector for the square matrix A of order n, we have a non-efficient vector for the corresponding square principal submatrix of order n-1 of A.</p></div>","PeriodicalId":18043,"journal":{"name":"Linear Algebra and its Applications","volume":null,"pages":null},"PeriodicalIF":1.0,"publicationDate":"2024-07-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.sciencedirect.com/science/article/pii/S0024379524002854/pdfft?md5=275e7043d1166d9276511bf66ea2c7ed&pid=1-s2.0-S0024379524002854-main.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141587727","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"P-matrix powers","authors":"","doi":"10.1016/j.laa.2024.07.002","DOIUrl":"10.1016/j.laa.2024.07.002","url":null,"abstract":"<div><p>A <em>P</em>-matrix is a matrix all of whose principal minors are positive. We demonstrate that the fractional powers of a <em>P</em>-matrix are also <em>P</em>-matrices. This insight allows us to affirmatively address a longstanding conjecture raised in Hershkowitz and Johnson (1986) <span><span>[8]</span></span>: It is shown that if <span><math><msup><mrow><mi>A</mi></mrow><mrow><mi>k</mi></mrow></msup></math></span> is a <em>P</em>-matrix for all positive integers <em>k</em>, then the eigenvalues of <em>A</em> are positive.</p></div>","PeriodicalId":18043,"journal":{"name":"Linear Algebra and its Applications","volume":null,"pages":null},"PeriodicalIF":1.0,"publicationDate":"2024-07-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141587728","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":"On the cohomology of restricted Heisenberg Lie algebras","authors":"","doi":"10.1016/j.laa.2024.06.027","DOIUrl":"10.1016/j.laa.2024.06.027","url":null,"abstract":"<div><p>We show that the Heisenberg Lie algebras over a field <span><math><mi>F</mi></math></span> of characteristic <span><math><mi>p</mi><mo>></mo><mn>0</mn></math></span> admit a family of restricted Lie algebras, and we classify all such non-isomorphic restricted Lie algebra structures. We use the ordinary 1- and 2-cohomology spaces with trivial coefficients to compute the restricted 1- and 2-cohomology spaces of these restricted Heisenberg Lie algebras. We describe the restricted 1-dimensional central extensions, including explicit formulas for the Lie brackets and <span><math><msup><mrow><mo>⋅</mo></mrow><mrow><mo>[</mo><mi>p</mi><mo>]</mo></mrow></msup></math></span>-operators.</p></div>","PeriodicalId":18043,"journal":{"name":"Linear Algebra and its Applications","volume":null,"pages":null},"PeriodicalIF":1.0,"publicationDate":"2024-07-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141587730","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":"Excessive symmetry can preclude cutoff","authors":"Eric Ramos , Graham White","doi":"10.1016/j.laa.2024.06.025","DOIUrl":"10.1016/j.laa.2024.06.025","url":null,"abstract":"<div><p>In this paper we look at the families of random walks arising from FI-graphs. One may think of these objects as families of nested graphs, each equipped with a natural action by a symmetric group <span><math><msub><mrow><mi>S</mi></mrow><mrow><mi>n</mi></mrow></msub></math></span>, such that these actions are compatible and transitive. Families of graphs of this form were introduced by the authors in <span>[9]</span>, while a systematic study of random walks on these families were considered in <span>[10]</span>. In the present work, we illustrate that these random walks never exhibit the so-called product condition, and therefore also never display total variation cutoff as defined by Aldous and Diaconis <span>[1]</span>. In particular, we provide a large family of algebro-combinatorially motivated examples of collections of Markov chains which satisfy some well-known algebraic heuristics for cutoff, while not actually having the property.</p></div>","PeriodicalId":18043,"journal":{"name":"Linear Algebra and its Applications","volume":null,"pages":null},"PeriodicalIF":1.0,"publicationDate":"2024-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141500556","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":"Strong consistency of an estimator by the truncated singular value decomposition for an errors-in-variables regression model with collinearity","authors":"Kensuke Aishima","doi":"10.1016/j.laa.2024.06.024","DOIUrl":"https://doi.org/10.1016/j.laa.2024.06.024","url":null,"abstract":"In this paper, we prove strong consistency of an estimator by the truncated singular value decomposition for a multivariate errors-in-variables linear regression model with collinearity. This result is an extension of Gleser's proof of the strong consistency of total least squares solutions to the case with modern rank constraints. While the usual discussion of consistency in the absence of solution uniqueness deals with the minimal norm solution, the contribution of this study is to develop a theory that shows the strong consistency of a set of solutions. The proof is based on properties of orthogonal projections, specifically properties of the Rayleigh-Ritz procedure for computing eigenvalues. This makes it suitable for targeting problems where some row vectors of the matrices do not contain noise. Therefore, this paper gives a proof for the regression model with the above condition on the row vectors, resulting in a natural generalization of the strong consistency for the standard TLS estimator.","PeriodicalId":18043,"journal":{"name":"Linear Algebra and its Applications","volume":null,"pages":null},"PeriodicalIF":1.1,"publicationDate":"2024-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141513562","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}