Pub Date : 2025-10-29DOI: 10.1016/j.laa.2025.10.032
Sarah Chehade , Andrea Delgado , Shuzhou Wang , Zhenhua Wang
In quantum computing, Trotter estimates are critical for enabling efficient simulation of quantum systems and quantum dynamics, help implement complex quantum algorithms, and provide a systematic way to control approximate errors. In this paper, we extend the analysis of Trotter-Suzuki approximations, including third and higher orders, to Jordan-Banach algebras. We solve an open problem in our earlier paper on the existence of second-order Trotter formula error estimation in Jordan-Banach algebras. To illustrate our work, we apply our formula to simulate Trotter-factorized spins, and show improvements in the approximations. Our approach demonstrates the adaptability of Trotter product formulas and estimates to non-associative settings, which offers new insights into the applications of Jordan algebra theory to operator dynamics.
{"title":"Error estimates and higher order Trotter product formulas in Jordan-Banach algebras","authors":"Sarah Chehade , Andrea Delgado , Shuzhou Wang , Zhenhua Wang","doi":"10.1016/j.laa.2025.10.032","DOIUrl":"10.1016/j.laa.2025.10.032","url":null,"abstract":"<div><div>In quantum computing, Trotter estimates are critical for enabling efficient simulation of quantum systems and quantum dynamics, help implement complex quantum algorithms, and provide a systematic way to control approximate errors. In this paper, we extend the analysis of Trotter-Suzuki approximations, including third and higher orders, to Jordan-Banach algebras. We solve an open problem in our earlier paper on the existence of second-order Trotter formula error estimation in Jordan-Banach algebras. To illustrate our work, we apply our formula to simulate Trotter-factorized spins, and show improvements in the approximations. Our approach demonstrates the adaptability of Trotter product formulas and estimates to non-associative settings, which offers new insights into the applications of Jordan algebra theory to operator dynamics.</div></div>","PeriodicalId":18043,"journal":{"name":"Linear Algebra and its Applications","volume":"730 ","pages":"Pages 430-449"},"PeriodicalIF":1.1,"publicationDate":"2025-10-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145418536","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}
Pub Date : 2025-10-28DOI: 10.1016/j.laa.2025.10.010
Juan C. Gutierrez Fernandez , E.O. Quintero Vanegas
In our article Nilpotent Linear Spaces and Albert's Problem [Linear Algebra Appl. 518 (2017) 57–78], the proof of Theorem 6 was incomplete, as a case was omitted. Here we supply the missing argument. The statement of Theorem 6, and all subsequent results depending on it, remain valid.
{"title":"Corrigendum to “Nilpotent linear spaces and Albert's Problem” [Linear Algebra Appl. 518 (2017) 57–78]","authors":"Juan C. Gutierrez Fernandez , E.O. Quintero Vanegas","doi":"10.1016/j.laa.2025.10.010","DOIUrl":"10.1016/j.laa.2025.10.010","url":null,"abstract":"<div><div>In our article Nilpotent Linear Spaces and Albert's Problem [Linear Algebra Appl. 518 (2017) 57–78], the proof of Theorem 6 was incomplete, as a case was omitted. Here we supply the missing argument. The statement of Theorem 6, and all subsequent results depending on it, remain valid.</div></div>","PeriodicalId":18043,"journal":{"name":"Linear Algebra and its Applications","volume":"730 ","pages":"Pages 313-317"},"PeriodicalIF":1.1,"publicationDate":"2025-10-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145419081","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}
Pub Date : 2025-10-27DOI: 10.1016/j.laa.2025.10.026
Rabi Marzouki, Khalid Souilah
In this article, we provide a complete description of all maps on the algebra of all bounded linear operators acting on an infinite-dimensional complex Banach space, that leave invariant the ascent, or descent, under the product of two operators.
{"title":"Non-linear maps preserving ascent or descent of product of operators","authors":"Rabi Marzouki, Khalid Souilah","doi":"10.1016/j.laa.2025.10.026","DOIUrl":"10.1016/j.laa.2025.10.026","url":null,"abstract":"<div><div>In this article, we provide a complete description of all maps on the algebra of all bounded linear operators acting on an infinite-dimensional complex Banach space, that leave invariant the ascent, or descent, under the product of two operators.</div></div>","PeriodicalId":18043,"journal":{"name":"Linear Algebra and its Applications","volume":"730 ","pages":"Pages 344-357"},"PeriodicalIF":1.1,"publicationDate":"2025-10-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145418522","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}
Pub Date : 2025-10-24DOI: 10.1016/j.laa.2025.10.025
Xinhui Duan, Lu Lu
The spectral Turán number denotes the maximum spectral radius of an F-free graph G of order n. This paper determines for sufficiently large n, establishing the unique extremal graph. Here, is the odd prism, which is the Cartesian product , where the Cartesian product has vertex set , and edges between and if either and , or and .
{"title":"Spectral extremal problem for the odd prism","authors":"Xinhui Duan, Lu Lu","doi":"10.1016/j.laa.2025.10.025","DOIUrl":"10.1016/j.laa.2025.10.025","url":null,"abstract":"<div><div>The spectral Turán number <span><math><mtext>spex</mtext><mo>(</mo><mi>n</mi><mo>,</mo><mi>F</mi><mo>)</mo></math></span> denotes the maximum spectral radius <span><math><mi>λ</mi><mo>(</mo><mi>G</mi><mo>)</mo></math></span> of an <em>F</em>-free graph <em>G</em> of order <em>n</em>. This paper determines <span><math><mtext>spex</mtext><mrow><mo>(</mo><mi>n</mi><mo>,</mo><msubsup><mrow><mi>C</mi></mrow><mrow><mn>2</mn><mi>k</mi><mo>+</mo><mn>1</mn></mrow><mrow><mo>□</mo></mrow></msubsup><mo>)</mo></mrow></math></span> for sufficiently large <em>n</em>, establishing the unique extremal graph. Here, <span><math><msubsup><mrow><mi>C</mi></mrow><mrow><mn>2</mn><mi>k</mi><mo>+</mo><mn>1</mn></mrow><mrow><mo>□</mo></mrow></msubsup></math></span> is the odd prism, which is the Cartesian product <span><math><msub><mrow><mi>C</mi></mrow><mrow><mn>2</mn><mi>k</mi><mo>+</mo><mn>1</mn></mrow></msub><mo>□</mo><msub><mrow><mi>K</mi></mrow><mrow><mn>2</mn></mrow></msub></math></span>, where the Cartesian product <span><math><mi>G</mi><mo>□</mo><mi>F</mi></math></span> has vertex set <span><math><mi>V</mi><mo>(</mo><mi>G</mi><mo>)</mo><mo>×</mo><mi>V</mi><mo>(</mo><mi>F</mi><mo>)</mo></math></span>, and edges between <span><math><mo>(</mo><msub><mrow><mi>u</mi></mrow><mrow><mn>1</mn></mrow></msub><mo>,</mo><msub><mrow><mi>v</mi></mrow><mrow><mn>1</mn></mrow></msub><mo>)</mo></math></span> and <span><math><mo>(</mo><msub><mrow><mi>u</mi></mrow><mrow><mn>2</mn></mrow></msub><mo>,</mo><msub><mrow><mi>v</mi></mrow><mrow><mn>2</mn></mrow></msub><mo>)</mo></math></span> if either <span><math><msub><mrow><mi>u</mi></mrow><mrow><mn>1</mn></mrow></msub><mo>=</mo><msub><mrow><mi>u</mi></mrow><mrow><mn>2</mn></mrow></msub></math></span> and <span><math><msub><mrow><mi>v</mi></mrow><mrow><mn>1</mn></mrow></msub><msub><mrow><mi>v</mi></mrow><mrow><mn>2</mn></mrow></msub><mo>∈</mo><mi>E</mi><mo>(</mo><mi>F</mi><mo>)</mo></math></span>, or <span><math><msub><mrow><mi>v</mi></mrow><mrow><mn>1</mn></mrow></msub><mo>=</mo><msub><mrow><mi>v</mi></mrow><mrow><mn>2</mn></mrow></msub></math></span> and <span><math><msub><mrow><mi>u</mi></mrow><mrow><mn>1</mn></mrow></msub><msub><mrow><mi>u</mi></mrow><mrow><mn>2</mn></mrow></msub><mo>∈</mo><mi>E</mi><mo>(</mo><mi>G</mi><mo>)</mo></math></span>.</div></div>","PeriodicalId":18043,"journal":{"name":"Linear Algebra and its Applications","volume":"730 ","pages":"Pages 276-296"},"PeriodicalIF":1.1,"publicationDate":"2025-10-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145418516","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}
Pub Date : 2025-10-24DOI: 10.1016/j.laa.2025.10.022
Frederik vom Ende , Dariusz Chruściński , Gen Kimura , Paolo Muratore-Ginanneschi
We prove an upper bound on the trace of any 2-positive, trace-preserving map in terms of its smallest eigenvalue. We show that this spectral bound is tight, and that 2-positivity is necessary for this inequality to hold in general. Moreover, we use this to infer a similar bound for generators of one-parameter semigroups of 2-positive trace-preserving maps. With this approach we generalize known results for completely positive trace-preserving dynamics while providing a significantly simpler proof that is entirely algebraic.
{"title":"Universal bound on the eigenvalues of 2-positive trace-preserving maps","authors":"Frederik vom Ende , Dariusz Chruściński , Gen Kimura , Paolo Muratore-Ginanneschi","doi":"10.1016/j.laa.2025.10.022","DOIUrl":"10.1016/j.laa.2025.10.022","url":null,"abstract":"<div><div>We prove an upper bound on the trace of any 2-positive, trace-preserving map in terms of its smallest eigenvalue. We show that this spectral bound is tight, and that 2-positivity is necessary for this inequality to hold in general. Moreover, we use this to infer a similar bound for generators of one-parameter semigroups of 2-positive trace-preserving maps. With this approach we generalize known results for completely positive trace-preserving dynamics while providing a significantly simpler proof that is entirely algebraic.</div></div>","PeriodicalId":18043,"journal":{"name":"Linear Algebra and its Applications","volume":"730 ","pages":"Pages 262-275"},"PeriodicalIF":1.1,"publicationDate":"2025-10-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145419086","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}
Pub Date : 2025-10-24DOI: 10.1016/j.laa.2025.10.020
Johannes M. Schumacher
In a variety of applications, the problem comes up of describing the principal part of the inverse of a holomorphic operator at an eigenvalue in terms of left and right root functions associated to the eigenvalue. Such a description was given by Keldysh in 1951. His theorem, the proof of which was published only in 1971, is a fundamental result in the local spectral theory of operator-valued functions. Here we present a streamlined derivation in the matrix case, and we extend Keldysh's theorem by means of a new principal part formula. Special attention is given to the semisimple case (first-order poles).
{"title":"Keldysh's theorem revisited","authors":"Johannes M. Schumacher","doi":"10.1016/j.laa.2025.10.020","DOIUrl":"10.1016/j.laa.2025.10.020","url":null,"abstract":"<div><div>In a variety of applications, the problem comes up of describing the principal part of the inverse of a holomorphic operator at an eigenvalue in terms of left and right root functions associated to the eigenvalue. Such a description was given by Keldysh in 1951. His theorem, the proof of which was published only in 1971, is a fundamental result in the local spectral theory of operator-valued functions. Here we present a streamlined derivation in the matrix case, and we extend Keldysh's theorem by means of a new principal part formula. Special attention is given to the semisimple case (first-order poles).</div></div>","PeriodicalId":18043,"journal":{"name":"Linear Algebra and its Applications","volume":"730 ","pages":"Pages 358-386"},"PeriodicalIF":1.1,"publicationDate":"2025-10-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145418519","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}
Pub Date : 2025-10-24DOI: 10.1016/j.laa.2025.10.023
Jia Wei , Muhuo Liu , Zhifu You , Hong-Jian Lai
Let be the edge connectivity of a graph G. The strength of G, denoted by , is the maximum value of where H runs over all subgraphs of G. For a positive integer k, Mader in 1971 initiated the study of a simple graph G that does not have a subgraph with edge connectivity exceeding k but the addition of any edge to G will create a subgraph of edge connectivity at least . For any simple graph G on vertices with the spectral radius of , we will show the followings:
(i) If the minimum degree of G is at least k, and then unless G belongs to a well classified family of graphs.
(ii) If and , then there exists an edge such that unless G belongs to a well classified family of graphs.
{"title":"Spectral conditions for the maximum subgraph edge-connectivity of graphs","authors":"Jia Wei , Muhuo Liu , Zhifu You , Hong-Jian Lai","doi":"10.1016/j.laa.2025.10.023","DOIUrl":"10.1016/j.laa.2025.10.023","url":null,"abstract":"<div><div>Let <span><math><msup><mrow><mi>κ</mi></mrow><mrow><mo>′</mo></mrow></msup><mo>(</mo><mi>G</mi><mo>)</mo></math></span> be the edge connectivity of a graph <em>G</em>. The strength of <em>G</em>, denoted by <span><math><msup><mrow><mover><mrow><mi>κ</mi></mrow><mo>‾</mo></mover></mrow><mrow><mo>′</mo></mrow></msup><mo>(</mo><mi>G</mi><mo>)</mo></math></span>, is the maximum value of <span><math><msup><mrow><mi>κ</mi></mrow><mrow><mo>′</mo></mrow></msup><mo>(</mo><mi>H</mi><mo>)</mo></math></span> where <em>H</em> runs over all subgraphs of <em>G</em>. For a positive integer <em>k</em>, Mader in 1971 initiated the study of a simple graph <em>G</em> that does not have a subgraph with edge connectivity exceeding <em>k</em> but the addition of any edge to <em>G</em> will create a subgraph of edge connectivity at least <span><math><mi>k</mi><mo>+</mo><mn>1</mn></math></span>. For any simple graph <em>G</em> on <span><math><mi>n</mi><mo>≥</mo><mi>k</mi><mo>+</mo><mn>2</mn></math></span> vertices with the spectral radius of <span><math><mi>λ</mi><mo>(</mo><mi>G</mi><mo>)</mo></math></span>, we will show the followings:</div><div>(i) If the minimum degree of <em>G</em> is at least <em>k</em>, and<span><span><span><math><mi>λ</mi><mo>(</mo><mi>G</mi><mo>)</mo><mo>≥</mo><mfrac><mrow><mi>k</mi><mo>−</mo><mn>1</mn><mo>+</mo><msqrt><mrow><mn>4</mn><mi>n</mi><mi>k</mi><mo>−</mo><mn>3</mn><msup><mrow><mi>k</mi></mrow><mrow><mn>2</mn></mrow></msup><mo>−</mo><mn>2</mn><mi>k</mi><mo>+</mo><mn>1</mn></mrow></msqrt></mrow><mrow><mn>2</mn></mrow></mfrac><mo>,</mo></math></span></span></span> then <span><math><msup><mrow><mover><mrow><mi>κ</mi></mrow><mo>‾</mo></mover></mrow><mrow><mo>′</mo></mrow></msup><mo>(</mo><mi>G</mi><mo>)</mo><mo>></mo><mi>k</mi></math></span> unless <em>G</em> belongs to a well classified family of graphs.</div><div>(ii) If <span><math><mi>k</mi><mo>≥</mo><mn>2</mn></math></span> and <span><math><mi>λ</mi><mo>(</mo><mi>G</mi><mo>)</mo><mo>≤</mo><mi>k</mi><mo>+</mo><mn>1</mn></math></span>, then there exists an edge <span><math><mi>e</mi><mo>∈</mo><mi>E</mi><mo>(</mo><msup><mrow><mi>G</mi></mrow><mrow><mi>c</mi></mrow></msup><mo>)</mo></math></span> such that <span><math><msup><mrow><mover><mrow><mi>κ</mi></mrow><mo>‾</mo></mover></mrow><mrow><mo>′</mo></mrow></msup><mo>(</mo><mi>G</mi><mo>+</mo><mi>e</mi><mo>)</mo><mo>≤</mo><mi>k</mi></math></span> unless <em>G</em> belongs to a well classified family of graphs.</div></div>","PeriodicalId":18043,"journal":{"name":"Linear Algebra and its Applications","volume":"730 ","pages":"Pages 416-429"},"PeriodicalIF":1.1,"publicationDate":"2025-10-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145418535","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}
Pub Date : 2025-10-24DOI: 10.1016/j.laa.2025.10.018
Yurui Jiang , Junfeng Yin
Two-sided preconditioned CGLS method is proposed for solving large-scale rank-deficient factorized linear systems, where the original system is reformulated into an augmented linear system with a scaling parameter. A class of structured two-sided preconditioners based on sketching-and-QR strategy is studied in detail. The convergence theory of the proposed method is established and the properties of the preconditioned system are analyzed. Numerical experiments demonstrate that the proposed method with sketch-based preconditioners is efficient and outperforms existing approaches.
{"title":"Two-sided preconditioned CGLS for the solution of factorized linear systems","authors":"Yurui Jiang , Junfeng Yin","doi":"10.1016/j.laa.2025.10.018","DOIUrl":"10.1016/j.laa.2025.10.018","url":null,"abstract":"<div><div>Two-sided preconditioned CGLS method is proposed for solving large-scale rank-deficient factorized linear systems, where the original system is reformulated into an augmented linear system with a scaling parameter. A class of structured two-sided preconditioners based on sketching-and-QR strategy is studied in detail. The convergence theory of the proposed method is established and the properties of the preconditioned system are analyzed. Numerical experiments demonstrate that the proposed method with sketch-based preconditioners is efficient and outperforms existing approaches.</div></div>","PeriodicalId":18043,"journal":{"name":"Linear Algebra and its Applications","volume":"730 ","pages":"Pages 387-415"},"PeriodicalIF":1.1,"publicationDate":"2025-10-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145418534","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}
Pub Date : 2025-10-24DOI: 10.1016/j.laa.2025.10.021
Richard A. Brualdi , Geir Dahl
We introduce and study a new rank of -matrices generalizing both the binary rank and the term rank of -matrices. We call it the ±-rank of a -matrix. We establish several inequalities relating the different ranks, including ordinary real rank. Moreover, the ±-rank is discussed for certain classes of -matrices, such as alternating sign matrices (ASMs), network matrices, and matrices whose bipartite graph is a tree. Computationally the ±-rank is not easy to determine (like binary rank it may be an NP-hard problem), and we investigate several examples.
{"title":"The ±-rank of a (0,±1)-matrix","authors":"Richard A. Brualdi , Geir Dahl","doi":"10.1016/j.laa.2025.10.021","DOIUrl":"10.1016/j.laa.2025.10.021","url":null,"abstract":"<div><div>We introduce and study a new rank of <span><math><mo>(</mo><mn>0</mn><mo>,</mo><mo>±</mo><mn>1</mn><mo>)</mo></math></span>-matrices generalizing both the binary rank and the term rank of <span><math><mo>(</mo><mn>0</mn><mo>,</mo><mn>1</mn><mo>)</mo></math></span>-matrices. We call it the ±<em>-rank</em> of a <span><math><mo>(</mo><mn>0</mn><mo>,</mo><mo>±</mo><mn>1</mn><mo>)</mo></math></span>-matrix. We establish several inequalities relating the different ranks, including ordinary real rank. Moreover, the ±-rank is discussed for certain classes of <span><math><mo>(</mo><mn>0</mn><mo>,</mo><mo>±</mo><mn>1</mn><mo>)</mo></math></span>-matrices, such as alternating sign matrices (ASMs), network matrices, and matrices whose bipartite graph is a tree. Computationally the ±-rank is not easy to determine (like binary rank it may be an NP-hard problem), and we investigate several examples.</div></div>","PeriodicalId":18043,"journal":{"name":"Linear Algebra and its Applications","volume":"730 ","pages":"Pages 318-343"},"PeriodicalIF":1.1,"publicationDate":"2025-10-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145418520","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}
Pub Date : 2025-10-24DOI: 10.1016/j.laa.2025.10.024
George Brooks , William Linz , Linyuan Lu
The spread of a graph G is the difference between the largest and smallest eigenvalues of its adjacency matrix. Breen, Riasanovsky, Tait and Urschel recently determined the graph on n vertices with maximum spread for sufficiently large n. In this paper, we study a related question of maximizing the difference for a given pair over all graphs on n vertices. We give upper bounds for all pairs , exhibit an infinite family of pairs where the bound is tight, and show that for the pair the extremal example is unique. These results contribute to a line of inquiry pioneered by Nikiforov aiming to maximize different linear combinations of eigenvalues over all graphs on n vertices.
{"title":"Maximum spectral gaps of graphs","authors":"George Brooks , William Linz , Linyuan Lu","doi":"10.1016/j.laa.2025.10.024","DOIUrl":"10.1016/j.laa.2025.10.024","url":null,"abstract":"<div><div>The <em>spread</em> of a graph <em>G</em> is the difference <span><math><msub><mrow><mi>λ</mi></mrow><mrow><mn>1</mn></mrow></msub><mo>−</mo><msub><mrow><mi>λ</mi></mrow><mrow><mi>n</mi></mrow></msub></math></span> between the largest and smallest eigenvalues of its adjacency matrix. Breen, Riasanovsky, Tait and Urschel recently determined the graph on <em>n</em> vertices with maximum spread for sufficiently large <em>n</em>. In this paper, we study a related question of maximizing the difference <span><math><msub><mrow><mi>λ</mi></mrow><mrow><mi>i</mi><mo>+</mo><mn>1</mn></mrow></msub><mo>−</mo><msub><mrow><mi>λ</mi></mrow><mrow><mi>n</mi><mo>−</mo><mi>j</mi></mrow></msub></math></span> for a given pair <span><math><mo>(</mo><mi>i</mi><mo>,</mo><mi>j</mi><mo>)</mo></math></span> over all graphs on <em>n</em> vertices. We give upper bounds for all pairs <span><math><mo>(</mo><mi>i</mi><mo>,</mo><mi>j</mi><mo>)</mo></math></span>, exhibit an infinite family of pairs where the bound is tight, and show that for the pair <span><math><mo>(</mo><mn>1</mn><mo>,</mo><mn>0</mn><mo>)</mo></math></span> the extremal example is unique. These results contribute to a line of inquiry pioneered by Nikiforov aiming to maximize different linear combinations of eigenvalues over all graphs on <em>n</em> vertices.</div></div>","PeriodicalId":18043,"journal":{"name":"Linear Algebra and its Applications","volume":"730 ","pages":"Pages 297-312"},"PeriodicalIF":1.1,"publicationDate":"2025-10-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145419085","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}