{"title":"P-polynomial and bipartite coherent configurations","authors":"Sabrina Lato","doi":"10.1016/j.laa.2024.11.027","DOIUrl":"10.1016/j.laa.2024.11.027","url":null,"abstract":"<div><div>We introduce the notion of <em>P</em>-polynomial coherent configurations and show that they can have at most two fibers. We then introduce a class of two-fiber coherent configurations which have two distinguished bases for the coherent algebra, similar to the Bose-Mesner algebra of an association scheme. Examples of these bipartite coherent configurations include the <em>P</em>-polynomial class of distance-biregular graphs, as well as quasi-symmetric designs and strongly regular designs.</div></div>","PeriodicalId":18043,"journal":{"name":"Linear Algebra and its Applications","volume":"708 ","pages":"Pages 12-41"},"PeriodicalIF":1.0,"publicationDate":"2024-11-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143165266","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":"Tridiagonal M-matrices whose group inverses are tridiagonal","authors":"A.M. Encinas , K. Kranthi Priya , K.C. Sivakumar","doi":"10.1016/j.laa.2024.11.026","DOIUrl":"10.1016/j.laa.2024.11.026","url":null,"abstract":"<div><div>Recently, a characterization was obtained for a nonsingular <em>M</em>-matrix, to have a tridiagonal inverse. In a related work, the explicit sign pattern for this kind of matrices was also discovered. In this paper, we extend these results to singular <em>M</em>-matrices that are group invertible. Further, we obtain the precise sign pattern for such matrices. Our techniques and reasoning work for both singular and nonsingular matrices, thereby providing a unified framework to treat such classes of matrices.</div></div>","PeriodicalId":18043,"journal":{"name":"Linear Algebra and its Applications","volume":"708 ","pages":"Pages 42-60"},"PeriodicalIF":1.0,"publicationDate":"2024-11-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143165267","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":"Dominant subspace and low-rank approximations from block Krylov subspaces without a prescribed gap","authors":"Pedro Massey","doi":"10.1016/j.laa.2024.11.021","DOIUrl":"10.1016/j.laa.2024.11.021","url":null,"abstract":"<div><div>We develop a novel convergence analysis of the classical deterministic block Krylov methods for the approximation of <em>h</em>-dimensional dominant subspaces and low-rank approximations of matrices <span><math><mi>A</mi><mo>∈</mo><msup><mrow><mi>K</mi></mrow><mrow><mi>m</mi><mo>×</mo><mi>n</mi></mrow></msup></math></span> (where <span><math><mi>K</mi><mo>=</mo><mi>R</mi></math></span> or <span><math><mi>C</mi><mo>)</mo></math></span> in the case that there is no singular gap at the index <em>h</em> i.e., if <span><math><msub><mrow><mi>σ</mi></mrow><mrow><mi>h</mi></mrow></msub><mo>=</mo><msub><mrow><mi>σ</mi></mrow><mrow><mi>h</mi><mo>+</mo><mn>1</mn></mrow></msub></math></span> (where <span><math><msub><mrow><mi>σ</mi></mrow><mrow><mn>1</mn></mrow></msub><mo>≥</mo><mo>…</mo><mo>≥</mo><msub><mrow><mi>σ</mi></mrow><mrow><mi>p</mi></mrow></msub><mo>≥</mo><mn>0</mn></math></span> denote the singular values of <em>A</em>, and <span><math><mi>p</mi><mo>=</mo><mi>min</mi><mo></mo><mo>{</mo><mi>m</mi><mo>,</mo><mi>n</mi><mo>}</mo></math></span>). Indeed, starting with a (deterministic) matrix <span><math><mi>X</mi><mo>∈</mo><msup><mrow><mi>K</mi></mrow><mrow><mi>n</mi><mo>×</mo><mi>r</mi></mrow></msup></math></span> with <span><math><mi>r</mi><mo>≥</mo><mi>h</mi></math></span> satisfying a compatibility assumption with some <em>h</em>-dimensional right dominant subspace of <em>A</em>, we show that block Krylov methods produce arbitrarily good approximations for both problems mentioned above. Our approach is based on recent work by Drineas, Ipsen, Kontopoulou and Magdon-Ismail on the approximation of structural left dominant subspaces. The main difference between our work and previous work on this topic is that instead of exploiting a singular gap at the prescribed index <em>h</em> (which is zero in this case) we exploit the nearest existing singular gaps. We include a section with numerical examples that test the performance of our main results.</div></div>","PeriodicalId":18043,"journal":{"name":"Linear Algebra and its Applications","volume":"708 ","pages":"Pages 112-149"},"PeriodicalIF":1.0,"publicationDate":"2024-11-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143164619","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":"New existence results for conjoined bases of singular linear Hamiltonian systems with given Sturmian properties","authors":"Peter Šepitka, Roman Šimon Hilscher","doi":"10.1016/j.laa.2024.11.017","DOIUrl":"10.1016/j.laa.2024.11.017","url":null,"abstract":"<div><div>In this paper we derive new existence results for conjoined bases of singular linear Hamiltonian differential systems with given qualitative (Sturmian) properties. In particular, we examine the existence of conjoined bases with invertible upper block and with prescribed number of focal points at the endpoints of the considered unbounded interval. Such results are vital for the theory of Riccati differential equations and its applications in optimal control problems. As the main tools we use a new general characterization of conjoined bases belonging to a given equivalence class (genus) and the theory of comparative index of two Lagrangian planes. We also utilize extensively the methods of matrix analysis. The results are new even for identically normal linear Hamiltonian systems. The results are also new for linear Hamiltonian systems on a compact interval, where they provide additional equivalent conditions to the classical Reid roundabout theorem about disconjugacy.</div></div>","PeriodicalId":18043,"journal":{"name":"Linear Algebra and its Applications","volume":"707 ","pages":"Pages 187-224"},"PeriodicalIF":1.0,"publicationDate":"2024-11-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142748261","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":"Graded polynomial identities for the Jordan algebra of 2 × 2 upper triangular matrices","authors":"Dimas José Gonçalves , Mateus Eduardo Salomão","doi":"10.1016/j.laa.2024.11.022","DOIUrl":"10.1016/j.laa.2024.11.022","url":null,"abstract":"<div><div>Consider the Jordan algebra of upper triangular matrices of order two, over a field of characteristic different from two, with the Jordan product induced by the usual associative product. For every nontrivial group grading on such algebra, we describe the set of all its graded polynomial identities. Moreover, we describe a linear basis for the corresponding relatively free graded algebra.</div></div>","PeriodicalId":18043,"journal":{"name":"Linear Algebra and its Applications","volume":"708 ","pages":"Pages 61-92"},"PeriodicalIF":1.0,"publicationDate":"2024-11-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143165268","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":"The category of quasi-Whittaker modules over the Schrödinger algebra","authors":"Zhongping Ji , Genqiang Liu , Yueqiang Zhao","doi":"10.1016/j.laa.2024.11.023","DOIUrl":"10.1016/j.laa.2024.11.023","url":null,"abstract":"<div><div>Simple quasi-Whittaker modules over the Schrödinger algebra <span><math><msub><mrow><mi>s</mi></mrow><mrow><mn>1</mn></mrow></msub></math></span> of <span><math><mo>(</mo><mn>1</mn><mo>+</mo><mn>1</mn><mo>)</mo></math></span>-dimensional space-time were originally introduced and classified by Cai, Cheng, Shen in their work <span><span>[7]</span></span>. In the present paper, our focus lies in the study of the category of quasi-Whittaker modules over <span><math><msub><mrow><mi>s</mi></mrow><mrow><mn>1</mn></mrow></msub></math></span>. We show that each non-singular block is equivalent to the category of finite-dimensional modules over the polynomial algebra in one variable. In particular, we can give explicit realizations of simple quasi-Whittaker modules using differential operators.</div></div>","PeriodicalId":18043,"journal":{"name":"Linear Algebra and its Applications","volume":"708 ","pages":"Pages 1-11"},"PeriodicalIF":1.0,"publicationDate":"2024-11-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143165265","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":"Stabilization of associated prime ideals of monomial ideals – Bounding the copersistence index","authors":"Clemens Heuberger, Jutta Rath, Roswitha Rissner","doi":"10.1016/j.laa.2024.11.020","DOIUrl":"10.1016/j.laa.2024.11.020","url":null,"abstract":"<div><div>The sequence <span><math><msub><mrow><mo>(</mo><mi>Ass</mi><mo>(</mo><mi>R</mi><mo>/</mo><msup><mrow><mi>I</mi></mrow><mrow><mi>n</mi></mrow></msup><mo>)</mo><mo>)</mo></mrow><mrow><mi>n</mi><mo>∈</mo><mi>N</mi></mrow></msub></math></span> of associated primes of powers of a monomial ideal <em>I</em> in a polynomial ring <em>R</em> eventually stabilizes by a known result by Markus Brodmann. Lê Tuân Hoa gives an upper bound for the index where the stabilization occurs. This bound depends on the generators of the ideal and is obtained by separately bounding the powers of <em>I</em> after which said sequence is non-decreasing and non-increasing, respectively. In this paper, we focus on the latter and call the smallest such number the copersistence index. We take up the proof idea of Lê Tuân Hoa, who exploits a certain system of inequalities whose solution sets store information about the associated primes of powers of <em>I</em>. However, these proofs are entangled with a specific choice for the system of inequalities. In contrast to that, we present a generic ansatz to obtain an upper bound for the copersistence index that is uncoupled from this choice of the system. We establish properties for a system of inequalities to be eligible for this approach to work. We construct two suitable inequality systems to demonstrate how this ansatz yields upper bounds for the copersistence index and compare them with Hoa's. One of the two systems leads to an improvement of the bound by an exponential factor.</div></div>","PeriodicalId":18043,"journal":{"name":"Linear Algebra and its Applications","volume":"707 ","pages":"Pages 162-186"},"PeriodicalIF":1.0,"publicationDate":"2024-11-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142722539","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":"Characterization of almost-Riordan arrays with row sums","authors":"Yasemin Alp , E. Gokcen Kocer","doi":"10.1016/j.laa.2024.11.019","DOIUrl":"10.1016/j.laa.2024.11.019","url":null,"abstract":"<div><div>The almost-Riordan arrays and their inverses are investigating by the generating functions of the row sum, the alternating row sum, and the weighted row sum. The <em>A</em>, <em>Z</em>, and <em>ω</em>-sequences of the almost-Riordan arrays are characterized by the generating functions of these row sums. Additionally, using the generating functions of these row sums, the product of two almost-Riordan arrays is obtained.</div></div>","PeriodicalId":18043,"journal":{"name":"Linear Algebra and its Applications","volume":"706 ","pages":"Pages 101-123"},"PeriodicalIF":1.0,"publicationDate":"2024-11-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142722518","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":"Construction of symplectic solvmanifolds satisfying the hard-Lefschetz condition","authors":"Adrián Andrada, Agustín Garrone","doi":"10.1016/j.laa.2024.11.018","DOIUrl":"10.1016/j.laa.2024.11.018","url":null,"abstract":"<div><div>A compact symplectic manifold <span><math><mo>(</mo><mi>M</mi><mo>,</mo><mi>ω</mi><mo>)</mo></math></span> is said to satisfy the hard-Lefschetz condition if it is possible to develop an analogue of Hodge theory for <span><math><mo>(</mo><mi>M</mi><mo>,</mo><mi>ω</mi><mo>)</mo></math></span>. This loosely means that there is a notion of harmonicity of differential forms in <em>M</em>, depending on <em>ω</em> alone, such that every de Rham cohomology class in has a <em>ω</em>-harmonic representative. In this article, we study two non-equivalent families of diagonal almost-abelian Lie algebras that admit a distinguished almost-Kähler structure and compute their cohomology explicitly. We show that they satisfy the hard-Lefschetz condition with respect to any left-invariant symplectic structure by exploiting an unforeseen connection with Kneser graphs. We also show that for some choice of parameters their associated simply connected, completely solvable Lie groups admit lattices, thereby constructing examples of almost-Kähler solvmanifolds satisfying the hard-Lefschetz condition, in such a way that their de Rham cohomology is fully known.</div></div>","PeriodicalId":18043,"journal":{"name":"Linear Algebra and its Applications","volume":"706 ","pages":"Pages 70-100"},"PeriodicalIF":1.0,"publicationDate":"2024-11-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142722517","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":"Laplacian energies of vertices","authors":"J. Guerrero","doi":"10.1016/j.laa.2024.11.016","DOIUrl":"10.1016/j.laa.2024.11.016","url":null,"abstract":"<div><div>In this work, we define the Laplacian and Normalized Laplacian energies of vertices in a graph, we derive some of its properties and relate them to combinatorial, spectral and geometric quantities of the graph.</div></div>","PeriodicalId":18043,"journal":{"name":"Linear Algebra and its Applications","volume":"706 ","pages":"Pages 124-143"},"PeriodicalIF":1.0,"publicationDate":"2024-11-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142722519","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}