Pub Date : 2026-01-13DOI: 10.1016/j.laa.2026.01.010
Qingxiang Xu
Let be the set of all adjointable operators on a Hilbert -module H. For each , denotes its adjoint operator, and is the positive square root of . We establish simplified formulas for the matched projection of an idempotent as where I is the identity operator on H. These explicit expressions facilitate the straightforward derivation of several known properties of .
设L(H)是Hilbert C _ -模H上所有可伴随算子的集合。对于每一个T∈L(H), T _表示它的伴随算子,|T|是T _ T的正平方根。我们建立了幂等Q∈L(H) asm(Q)=I+|Q |−|I−Q|2= I+|Q|−|I−Q|2=2+|Q+Q |−|2−(Q+Q)|4的匹配投影m(Q)的简化公式,其中I是H上的恒等算子。这些显式表达式有助于直接推导出m(Q)的几个已知性质。
{"title":"Some simplified formulas for the matched projection of an idempotent","authors":"Qingxiang Xu","doi":"10.1016/j.laa.2026.01.010","DOIUrl":"10.1016/j.laa.2026.01.010","url":null,"abstract":"<div><div>Let <span><math><mi>L</mi><mo>(</mo><mi>H</mi><mo>)</mo></math></span> be the set of all adjointable operators on a Hilbert <span><math><msup><mrow><mi>C</mi></mrow><mrow><mo>⁎</mo></mrow></msup></math></span>-module <em>H</em>. For each <span><math><mi>T</mi><mo>∈</mo><mi>L</mi><mo>(</mo><mi>H</mi><mo>)</mo></math></span>, <span><math><msup><mrow><mi>T</mi></mrow><mrow><mo>⁎</mo></mrow></msup></math></span> denotes its adjoint operator, and <span><math><mo>|</mo><mi>T</mi><mo>|</mo></math></span> is the positive square root of <span><math><msup><mrow><mi>T</mi></mrow><mrow><mo>⁎</mo></mrow></msup><mi>T</mi></math></span>. We establish simplified formulas for the matched projection <span><math><mi>m</mi><mo>(</mo><mi>Q</mi><mo>)</mo></math></span> of an idempotent <span><math><mi>Q</mi><mo>∈</mo><mi>L</mi><mo>(</mo><mi>H</mi><mo>)</mo></math></span> as<span><span><span><math><mi>m</mi><mo>(</mo><mi>Q</mi><mo>)</mo><mo>=</mo><mfrac><mrow><mi>I</mi><mo>+</mo><mo>|</mo><msup><mrow><mi>Q</mi></mrow><mrow><mo>⁎</mo></mrow></msup><mo>|</mo><mo>−</mo><mo>|</mo><mi>I</mi><mo>−</mo><msup><mrow><mi>Q</mi></mrow><mrow><mo>⁎</mo></mrow></msup><mo>|</mo></mrow><mrow><mn>2</mn></mrow></mfrac><mo>=</mo><mfrac><mrow><mi>I</mi><mo>+</mo><mo>|</mo><mi>Q</mi><mo>|</mo><mo>−</mo><mo>|</mo><mi>I</mi><mo>−</mo><mi>Q</mi><mo>|</mo></mrow><mrow><mn>2</mn></mrow></mfrac><mo>=</mo><mfrac><mrow><mn>2</mn><mo>+</mo><mo>|</mo><mi>Q</mi><mo>+</mo><msup><mrow><mi>Q</mi></mrow><mrow><mo>⁎</mo></mrow></msup><mo>|</mo><mo>−</mo><mo>|</mo><mn>2</mn><mo>−</mo><mo>(</mo><mi>Q</mi><mo>+</mo><msup><mrow><mi>Q</mi></mrow><mrow><mo>⁎</mo></mrow></msup><mo>)</mo><mo>|</mo></mrow><mrow><mn>4</mn></mrow></mfrac><mo>,</mo></math></span></span></span> where <em>I</em> is the identity operator on <em>H</em>. These explicit expressions facilitate the straightforward derivation of several known properties of <span><math><mi>m</mi><mo>(</mo><mi>Q</mi><mo>)</mo></math></span>.</div></div>","PeriodicalId":18043,"journal":{"name":"Linear Algebra and its Applications","volume":"735 ","pages":"Pages 105-111"},"PeriodicalIF":1.1,"publicationDate":"2026-01-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146036322","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 : 2026-01-13DOI: 10.1016/j.laa.2026.01.004
Shib Sankar Saha , Swarup Kumar Panda
The energy of a hypergraph is defined as the sum of the absolute values of the eigenvalues of its adjacency matrix . In 2022, K. Cardoso et al. showed through examples that removing an arbitrary hyperedge from a hypergraph may increase, decrease, or leave its energy unchanged. In this article, we prove that for a k-uniform complete hypergraph and a 3-uniform complete bipartite hypergraph, the energy always decreases when an arbitrary hyperedge is deleted. Furthermore, we establish both lower and upper bounds for the energy of k-uniform hypergraphs in terms of the minimum degree and the strong chromatic number.
{"title":"Bounds on hypergraph energy and its variation under arbitrary hyperedge deletion","authors":"Shib Sankar Saha , Swarup Kumar Panda","doi":"10.1016/j.laa.2026.01.004","DOIUrl":"10.1016/j.laa.2026.01.004","url":null,"abstract":"<div><div>The energy of a hypergraph <span><math><mi>H</mi></math></span> is defined as the sum of the absolute values of the eigenvalues of its adjacency matrix <span><math><mi>A</mi><mo>(</mo><mi>H</mi><mo>)</mo></math></span>. In 2022, K. Cardoso et al. showed through examples that removing an arbitrary hyperedge from a hypergraph may increase, decrease, or leave its energy unchanged. In this article, we prove that for a <em>k</em>-uniform complete hypergraph and a 3-uniform complete bipartite hypergraph, the energy always decreases when an arbitrary hyperedge is deleted. Furthermore, we establish both lower and upper bounds for the energy of <em>k</em>-uniform hypergraphs in terms of the minimum degree and the strong chromatic number.</div></div>","PeriodicalId":18043,"journal":{"name":"Linear Algebra and its Applications","volume":"735 ","pages":"Pages 31-56"},"PeriodicalIF":1.1,"publicationDate":"2026-01-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145969254","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 : 2026-01-13DOI: 10.1016/j.laa.2026.01.007
Diego Aranda-Orna , Alejandra S. Córdova-Martínez
The aim of this paper is to define and study the constructions of alternating and symmetric (super)powers of metric generalized Jordan (super)pairs. These constructions are obtained by transference via the Faulkner construction. The construction of tensor (super)products for metric generalized Jordan (super)pairs is revisited. We always assume that the characteristic of the base field is different from 2; in case of positive characteristic, sometimes we require that the characteristic is large enough to allow nondegeneracy of certain bilinear forms.
{"title":"Alternating and symmetric superpowers of metric generalized Jordan superpairs","authors":"Diego Aranda-Orna , Alejandra S. Córdova-Martínez","doi":"10.1016/j.laa.2026.01.007","DOIUrl":"10.1016/j.laa.2026.01.007","url":null,"abstract":"<div><div>The aim of this paper is to define and study the constructions of alternating and symmetric (super)powers of metric generalized Jordan (super)pairs. These constructions are obtained by transference via the Faulkner construction. The construction of tensor (super)products for metric generalized Jordan (super)pairs is revisited. We always assume that the characteristic of the base field <span><math><mi>F</mi></math></span> is different from 2; in case of positive characteristic, sometimes we require that the characteristic is large enough to allow nondegeneracy of certain bilinear forms.</div></div>","PeriodicalId":18043,"journal":{"name":"Linear Algebra and its Applications","volume":"735 ","pages":"Pages 57-104"},"PeriodicalIF":1.1,"publicationDate":"2026-01-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145969255","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 : 2026-01-13DOI: 10.1016/j.laa.2026.01.012
Lele Liu , Bo Ning
We establish a spectral counterpart to Ore's problem (1962) which asks for the maximum size of an n-vertex graph such that its complement is connected and does not contain as a subgraph, where is a clique of order . Specifically, we characterize the unique graph achieving the maximum spectral radius among all n-vertex, -free graphs with connected complements. The proof strategy combines the association of the extremal graph with an auxiliary tree to infer its structure and technical spectral analysis of the extremal graphs' Perron vector.
{"title":"A spectral analogue of Ore's problem on Turán theorem","authors":"Lele Liu , Bo Ning","doi":"10.1016/j.laa.2026.01.012","DOIUrl":"10.1016/j.laa.2026.01.012","url":null,"abstract":"<div><div>We establish a spectral counterpart to Ore's problem (1962) which asks for the maximum size of an <em>n</em>-vertex graph such that its complement is connected and does not contain <span><math><msub><mrow><mi>K</mi></mrow><mrow><mi>r</mi><mo>+</mo><mn>1</mn></mrow></msub></math></span> as a subgraph, where <span><math><msub><mrow><mi>K</mi></mrow><mrow><mi>r</mi><mo>+</mo><mn>1</mn></mrow></msub></math></span> is a clique of order <span><math><mi>r</mi><mo>+</mo><mn>1</mn></math></span>. Specifically, we characterize the unique graph achieving the maximum spectral radius among all <em>n</em>-vertex, <span><math><msub><mrow><mi>K</mi></mrow><mrow><mi>r</mi><mo>+</mo><mn>1</mn></mrow></msub></math></span>-free graphs with connected complements. The proof strategy combines the association of the extremal graph with an auxiliary tree to infer its structure and technical spectral analysis of the extremal graphs' Perron vector.</div></div>","PeriodicalId":18043,"journal":{"name":"Linear Algebra and its Applications","volume":"735 ","pages":"Pages 112-122"},"PeriodicalIF":1.1,"publicationDate":"2026-01-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146036316","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 : 2026-01-12DOI: 10.1016/j.laa.2026.01.003
Fumio Hiai
In this paper, for , and positive semidefinite matrices A and B, we consider the quasi-extensions of several α-weighted geometric type matrix means such as the α-weighted geometric mean in Kubo–Ando's sense, the Rényi mean, etc. The log-majorization is examined for pairs of those α-weighted geometric type means. The joint concavity/convexity of the trace functions is also discussed based on theory of quantum divergences.
本文对α∈(0,∞)∈{1},p>;0和正半定矩阵A和B,考虑了几个α-加权几何型矩阵均值m - α,p(A,B):= m - α(Ap,Bp)1/p的拟扩展,如Kubo-Ando意义上的α-加权几何均值,rsamnyi均值等。对这些α-加权几何型均值的对(M,N),检验了Mα,p(A,B),q(A,B)的对数化。基于量子散度理论讨论了迹函数TrMα,p的联合凹凸性。
{"title":"Log-majorizations between quasi-geometric type means for matrices","authors":"Fumio Hiai","doi":"10.1016/j.laa.2026.01.003","DOIUrl":"10.1016/j.laa.2026.01.003","url":null,"abstract":"<div><div>In this paper, for <span><math><mi>α</mi><mo>∈</mo><mo>(</mo><mn>0</mn><mo>,</mo><mo>∞</mo><mo>)</mo><mo>∖</mo><mo>{</mo><mn>1</mn><mo>}</mo></math></span>, <span><math><mi>p</mi><mo>></mo><mn>0</mn></math></span> and positive semidefinite matrices <em>A</em> and <em>B</em>, we consider the quasi-extensions <span><math><msub><mrow><mi>M</mi></mrow><mrow><mi>α</mi><mo>,</mo><mi>p</mi></mrow></msub><mo>(</mo><mi>A</mi><mo>,</mo><mi>B</mi><mo>)</mo><mo>:</mo><mo>=</mo><msub><mrow><mi>M</mi></mrow><mrow><mi>α</mi></mrow></msub><msup><mrow><mo>(</mo><msup><mrow><mi>A</mi></mrow><mrow><mi>p</mi></mrow></msup><mo>,</mo><msup><mrow><mi>B</mi></mrow><mrow><mi>p</mi></mrow></msup><mo>)</mo></mrow><mrow><mn>1</mn><mo>/</mo><mi>p</mi></mrow></msup></math></span> of several <em>α</em>-weighted geometric type matrix means <span><math><msub><mrow><mi>M</mi></mrow><mrow><mi>α</mi></mrow></msub><mo>(</mo><mi>A</mi><mo>,</mo><mi>B</mi><mo>)</mo></math></span> such as the <em>α</em>-weighted geometric mean in Kubo–Ando's sense, the Rényi mean, etc. The log-majorization <span><math><msub><mrow><mi>M</mi></mrow><mrow><mi>α</mi><mo>,</mo><mi>p</mi></mrow></msub><mo>(</mo><mi>A</mi><mo>,</mo><mi>B</mi><mo>)</mo><msub><mrow><mo>≺</mo></mrow><mrow><mi>log</mi></mrow></msub><msub><mrow><mi>N</mi></mrow><mrow><mi>α</mi><mo>,</mo><mi>q</mi></mrow></msub><mo>(</mo><mi>A</mi><mo>,</mo><mi>B</mi><mo>)</mo></math></span> is examined for pairs <span><math><mo>(</mo><mi>M</mi><mo>,</mo><mi>N</mi><mo>)</mo></math></span> of those <em>α</em>-weighted geometric type means. The joint concavity/convexity of the trace functions <span><math><mrow><mi>Tr</mi></mrow><mspace></mspace><msub><mrow><mi>M</mi></mrow><mrow><mi>α</mi><mo>,</mo><mi>p</mi></mrow></msub></math></span> is also discussed based on theory of quantum divergences.</div></div>","PeriodicalId":18043,"journal":{"name":"Linear Algebra and its Applications","volume":"735 ","pages":"Pages 123-174"},"PeriodicalIF":1.1,"publicationDate":"2026-01-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146036321","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}
<div><div>Suppose <span><math><mi>A</mi><mo>=</mo><mo>[</mo><msub><mrow><mi>a</mi></mrow><mrow><mi>i</mi><mi>j</mi></mrow></msub><mo>]</mo><mo>∈</mo><msub><mrow><mi>M</mi></mrow><mrow><mi>n</mi></mrow></msub><mo>(</mo><mi>C</mi><mo>)</mo></math></span> is a complex <span><math><mi>n</mi><mo>×</mo><mi>n</mi></math></span> matrix and <span><math><mi>B</mi><mo>∈</mo><mi>B</mi><mo>(</mo><mi>H</mi><mo>)</mo></math></span> is a bounded linear operator on a complex Hilbert space <span><math><mi>H</mi></math></span>. We show that <span><math><mi>w</mi><mo>(</mo><mi>A</mi><mo>⊗</mo><mi>B</mi><mo>)</mo><mo>≤</mo><mi>w</mi><mo>(</mo><mi>C</mi><mo>)</mo></math></span>, where <span><math><mi>w</mi><mo>(</mo><mo>⋅</mo><mo>)</mo></math></span> denotes the numerical radius and <span><math><mi>C</mi><mo>=</mo><mo>[</mo><msub><mrow><mi>c</mi></mrow><mrow><mi>i</mi><mi>j</mi></mrow></msub><mo>]</mo></math></span> with <span><math><msub><mrow><mi>c</mi></mrow><mrow><mi>i</mi><mi>j</mi></mrow></msub><mo>=</mo><mi>w</mi><mrow><mo>(</mo><mrow><mo>[</mo><mtable><mtr><mtd><mn>0</mn></mtd><mtd><msub><mrow><mi>a</mi></mrow><mrow><mi>i</mi><mi>j</mi></mrow></msub></mtd></mtr><mtr><mtd><msub><mrow><mi>a</mi></mrow><mrow><mi>j</mi><mi>i</mi></mrow></msub></mtd><mtd><mn>0</mn></mtd></mtr></mtable><mo>]</mo></mrow><mo>⊗</mo><mi>B</mi><mo>)</mo></mrow></math></span>. This refines Holbrook's classical bound <span><math><mi>w</mi><mo>(</mo><mi>A</mi><mo>⊗</mo><mi>B</mi><mo>)</mo><mo>≤</mo><mi>w</mi><mo>(</mo><mi>A</mi><mo>)</mo><mo>‖</mo><mi>B</mi><mo>‖</mo></math></span> (1969) <span><span>[31]</span></span>, when all entries of <em>A</em> are non-negative. If moreover <span><math><msub><mrow><mi>a</mi></mrow><mrow><mi>i</mi><mi>i</mi></mrow></msub><mo>≠</mo><mn>0</mn></math></span> ∀<em>i</em>, we prove that <span><math><mi>w</mi><mo>(</mo><mi>A</mi><mo>⊗</mo><mi>B</mi><mo>)</mo><mo>=</mo><mi>w</mi><mo>(</mo><mi>A</mi><mo>)</mo><mo>‖</mo><mi>B</mi><mo>‖</mo></math></span> if and only if <span><math><mi>w</mi><mo>(</mo><mi>B</mi><mo>)</mo><mo>=</mo><mo>‖</mo><mi>B</mi><mo>‖</mo></math></span>. We then extend these and other results to the more general setting of semi-Hilbertian spaces induced by a positive operator.</div><div>In the reverse direction, we also specialize these results to Kronecker products and hence to Schur/entrywise products, of matrices: (1)(a) We first provide an alternate proof (using <span><math><mi>w</mi><mo>(</mo><mi>A</mi><mo>)</mo></math></span>) of a result of Goldberg and Zwas (1974) <span><span>[24]</span></span> that if the spectral norm of <em>A</em> equals its spectral radius, then each Jordan block for each maximum-modulus eigenvalue must be <span><math><mn>1</mn><mo>×</mo><mn>1</mn></math></span> (“partial diagonalizability”). (b) Using our approach, we further show given <span><math><mi>m</mi><mo>≥</mo><mn>1</mn></math></span> that <span><math><mi>w</mi><mo>(</mo><msup><mrow><mi>A</mi></mrow><mrow><mo>∘</mo><mi>m</mi></mrow></msup><mo>)</mo><mo>
{"title":"Numerical radius and ℓp operator norm of Kronecker products and Schur powers: inequalities and equalities","authors":"Pintu Bhunia , Sujit Sakharam Damase , Apoorva Khare","doi":"10.1016/j.laa.2026.01.005","DOIUrl":"10.1016/j.laa.2026.01.005","url":null,"abstract":"<div><div>Suppose <span><math><mi>A</mi><mo>=</mo><mo>[</mo><msub><mrow><mi>a</mi></mrow><mrow><mi>i</mi><mi>j</mi></mrow></msub><mo>]</mo><mo>∈</mo><msub><mrow><mi>M</mi></mrow><mrow><mi>n</mi></mrow></msub><mo>(</mo><mi>C</mi><mo>)</mo></math></span> is a complex <span><math><mi>n</mi><mo>×</mo><mi>n</mi></math></span> matrix and <span><math><mi>B</mi><mo>∈</mo><mi>B</mi><mo>(</mo><mi>H</mi><mo>)</mo></math></span> is a bounded linear operator on a complex Hilbert space <span><math><mi>H</mi></math></span>. We show that <span><math><mi>w</mi><mo>(</mo><mi>A</mi><mo>⊗</mo><mi>B</mi><mo>)</mo><mo>≤</mo><mi>w</mi><mo>(</mo><mi>C</mi><mo>)</mo></math></span>, where <span><math><mi>w</mi><mo>(</mo><mo>⋅</mo><mo>)</mo></math></span> denotes the numerical radius and <span><math><mi>C</mi><mo>=</mo><mo>[</mo><msub><mrow><mi>c</mi></mrow><mrow><mi>i</mi><mi>j</mi></mrow></msub><mo>]</mo></math></span> with <span><math><msub><mrow><mi>c</mi></mrow><mrow><mi>i</mi><mi>j</mi></mrow></msub><mo>=</mo><mi>w</mi><mrow><mo>(</mo><mrow><mo>[</mo><mtable><mtr><mtd><mn>0</mn></mtd><mtd><msub><mrow><mi>a</mi></mrow><mrow><mi>i</mi><mi>j</mi></mrow></msub></mtd></mtr><mtr><mtd><msub><mrow><mi>a</mi></mrow><mrow><mi>j</mi><mi>i</mi></mrow></msub></mtd><mtd><mn>0</mn></mtd></mtr></mtable><mo>]</mo></mrow><mo>⊗</mo><mi>B</mi><mo>)</mo></mrow></math></span>. This refines Holbrook's classical bound <span><math><mi>w</mi><mo>(</mo><mi>A</mi><mo>⊗</mo><mi>B</mi><mo>)</mo><mo>≤</mo><mi>w</mi><mo>(</mo><mi>A</mi><mo>)</mo><mo>‖</mo><mi>B</mi><mo>‖</mo></math></span> (1969) <span><span>[31]</span></span>, when all entries of <em>A</em> are non-negative. If moreover <span><math><msub><mrow><mi>a</mi></mrow><mrow><mi>i</mi><mi>i</mi></mrow></msub><mo>≠</mo><mn>0</mn></math></span> ∀<em>i</em>, we prove that <span><math><mi>w</mi><mo>(</mo><mi>A</mi><mo>⊗</mo><mi>B</mi><mo>)</mo><mo>=</mo><mi>w</mi><mo>(</mo><mi>A</mi><mo>)</mo><mo>‖</mo><mi>B</mi><mo>‖</mo></math></span> if and only if <span><math><mi>w</mi><mo>(</mo><mi>B</mi><mo>)</mo><mo>=</mo><mo>‖</mo><mi>B</mi><mo>‖</mo></math></span>. We then extend these and other results to the more general setting of semi-Hilbertian spaces induced by a positive operator.</div><div>In the reverse direction, we also specialize these results to Kronecker products and hence to Schur/entrywise products, of matrices: (1)(a) We first provide an alternate proof (using <span><math><mi>w</mi><mo>(</mo><mi>A</mi><mo>)</mo></math></span>) of a result of Goldberg and Zwas (1974) <span><span>[24]</span></span> that if the spectral norm of <em>A</em> equals its spectral radius, then each Jordan block for each maximum-modulus eigenvalue must be <span><math><mn>1</mn><mo>×</mo><mn>1</mn></math></span> (“partial diagonalizability”). (b) Using our approach, we further show given <span><math><mi>m</mi><mo>≥</mo><mn>1</mn></math></span> that <span><math><mi>w</mi><mo>(</mo><msup><mrow><mi>A</mi></mrow><mrow><mo>∘</mo><mi>m</mi></mrow></msup><mo>)</mo><mo>","PeriodicalId":18043,"journal":{"name":"Linear Algebra and its Applications","volume":"735 ","pages":"Pages 1-30"},"PeriodicalIF":1.1,"publicationDate":"2026-01-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145969253","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 : 2026-01-09DOI: 10.1016/j.laa.2026.01.006
Hassane Benbouziane, Kaddour Chadli, Mustapha Ech-chérif El Kettani
Let be the algebra of all bounded linear operators on an infinite-dimensional complex Banach space . For a fixed integer , an operator is called k-potent operator if . In this paper, we provide a complete description of all surjective and weakly continuous maps such that is k-potent operator if and only if is k-potent operator, for any and . We also give the result in the setting of complex Hilbert spaces without the hypothesis of continuity.
{"title":"Maps on B(X) preserving k-potent operators","authors":"Hassane Benbouziane, Kaddour Chadli, Mustapha Ech-chérif El Kettani","doi":"10.1016/j.laa.2026.01.006","DOIUrl":"10.1016/j.laa.2026.01.006","url":null,"abstract":"<div><div>Let <span><math><mi>B</mi><mo>(</mo><mi>X</mi><mo>)</mo></math></span> be the algebra of all bounded linear operators on an infinite-dimensional complex Banach space <span><math><mi>X</mi></math></span>. For a fixed integer <span><math><mi>k</mi><mo>≥</mo><mn>2</mn></math></span>, an operator <span><math><mi>A</mi><mo>∈</mo><mi>B</mi><mo>(</mo><mi>X</mi><mo>)</mo></math></span> is called <em>k</em>-potent operator if <span><math><msup><mrow><mi>A</mi></mrow><mrow><mi>k</mi></mrow></msup><mo>=</mo><mi>A</mi></math></span>. In this paper, we provide a complete description of all surjective and weakly continuous maps <span><math><mi>Φ</mi><mo>:</mo><mi>B</mi><mo>(</mo><mi>X</mi><mo>)</mo><mo>→</mo><mi>B</mi><mo>(</mo><mi>X</mi><mo>)</mo></math></span> such that <span><math><mi>A</mi><mo>−</mo><mi>λ</mi><mi>B</mi></math></span> is <em>k</em>-potent operator if and only if <span><math><mi>Φ</mi><mo>(</mo><mi>A</mi><mo>)</mo><mo>−</mo><mi>λ</mi><mi>Φ</mi><mo>(</mo><mi>B</mi><mo>)</mo></math></span> is <em>k</em>-potent operator, for any <span><math><mi>A</mi><mo>,</mo><mi>B</mi><mo>∈</mo><mi>B</mi><mo>(</mo><mi>X</mi><mo>)</mo></math></span> and <span><math><mi>λ</mi><mo>∈</mo><mi>C</mi></math></span>. We also give the result in the setting of complex Hilbert spaces without the hypothesis of continuity.</div></div>","PeriodicalId":18043,"journal":{"name":"Linear Algebra and its Applications","volume":"734 ","pages":"Pages 152-175"},"PeriodicalIF":1.1,"publicationDate":"2026-01-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145979682","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 : 2026-01-07DOI: 10.1016/j.laa.2025.12.020
Ivan Shestakov , Ualbai Umirbaev
We study an analogue of the Andreadakis–Johnson filtration for automorphism groups of free algebras and introduce the notion of tangent Lie algebras for certain automorphism groups, defined as subalgebras of the Lie algebra of derivations. We show that, for many classical varieties of algebras, the tangent Lie algebra is contained in the Lie algebra of derivations with constant divergence. We also introduce the concepts of approximately tame and absolutely wild automorphisms of free algebras in arbitrary varieties and employ tangent Lie algebras to investigate their properties. It is shown that nearly all known examples of wild automorphisms of free algebras are absolutely wild, with the notable exceptions of the Nagata and Anick automorphisms. We show that the Bergman automorphism of free matrix algebras of order two is absolutely wild. Furthermore, we prove that free algebras in any variety of polynilpotent Lie algebras–except for the abelian and metabelian varieties–also possess absolutely wild automorphisms.
{"title":"Tangent Lie algebras of automorphism groups of free algebras","authors":"Ivan Shestakov , Ualbai Umirbaev","doi":"10.1016/j.laa.2025.12.020","DOIUrl":"10.1016/j.laa.2025.12.020","url":null,"abstract":"<div><div>We study an analogue of the Andreadakis–Johnson filtration for automorphism groups of free algebras and introduce the notion of tangent Lie algebras for certain automorphism groups, defined as subalgebras of the Lie algebra of derivations. We show that, for many classical varieties of algebras, the tangent Lie algebra is contained in the Lie algebra of derivations with constant divergence. We also introduce the concepts of approximately tame and absolutely wild automorphisms of free algebras in arbitrary varieties and employ tangent Lie algebras to investigate their properties. It is shown that nearly all known examples of wild automorphisms of free algebras are absolutely wild, with the notable exceptions of the Nagata and Anick automorphisms. We show that the Bergman automorphism of free matrix algebras of order two is absolutely wild. Furthermore, we prove that free algebras in any variety of polynilpotent Lie algebras–except for the abelian and metabelian varieties–also possess absolutely wild automorphisms.</div></div>","PeriodicalId":18043,"journal":{"name":"Linear Algebra and its Applications","volume":"734 ","pages":"Pages 193-223"},"PeriodicalIF":1.1,"publicationDate":"2026-01-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145979684","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 : 2026-01-06DOI: 10.1016/j.laa.2026.01.001
Richard A. Brualdi
{"title":"From the Editor-in-Chief","authors":"Richard A. Brualdi","doi":"10.1016/j.laa.2026.01.001","DOIUrl":"10.1016/j.laa.2026.01.001","url":null,"abstract":"","PeriodicalId":18043,"journal":{"name":"Linear Algebra and its Applications","volume":"734 ","pages":"Pages 116-117"},"PeriodicalIF":1.1,"publicationDate":"2026-01-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145928389","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 : 2026-01-06DOI: 10.1016/j.laa.2026.01.002
Fernando De Terán , Bruno Iannazzo
We provide a characterization for a periodic system of generalized Sylvester and conjugate-Sylvester equations, with at most one generalized conjugate-Sylvester equation, to have a unique solution when all coefficient matrices are square and all unknown matrices of the system have the same size. We also present a procedure to reduce an arbitrary system of generalized Sylvester and conjugate-Sylvester equations to periodic systems having at most one generalized conjugate-Sylvester equation. Therefore, the obtained characterization for the uniqueness of solution of periodic systems provides a characterization for general systems of generalized Sylvester and conjugate-Sylvester equations.
{"title":"Systems of standard and conjugate Sylvester equations: a characterization for the uniqueness of solution","authors":"Fernando De Terán , Bruno Iannazzo","doi":"10.1016/j.laa.2026.01.002","DOIUrl":"10.1016/j.laa.2026.01.002","url":null,"abstract":"<div><div>We provide a characterization for a periodic system of generalized Sylvester and conjugate-Sylvester equations, with at most one generalized conjugate-Sylvester equation, to have a unique solution when all coefficient matrices are square and all unknown matrices of the system have the same size. We also present a procedure to reduce an arbitrary system of generalized Sylvester and conjugate-Sylvester equations to periodic systems having at most one generalized conjugate-Sylvester equation. Therefore, the obtained characterization for the uniqueness of solution of periodic systems provides a characterization for general systems of generalized Sylvester and conjugate-Sylvester equations.</div></div>","PeriodicalId":18043,"journal":{"name":"Linear Algebra and its Applications","volume":"734 ","pages":"Pages 176-192"},"PeriodicalIF":1.1,"publicationDate":"2026-01-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145979683","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}