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For a simple graph G on n vertices the Seidel Estrada index of G, denoted by $ SEE(G) $ SEE (G) , is defined as $ SEE(G)=\sum _{i=1}^ne^{\theta _i} $ SEE (G) = ∑ i = 1 n e θ i , where $ \theta _1,\ldots,\theta _n $ θ 1 , ... , θ n are the Seidel eigenvalues (the eigenvalues of the Seidel matrix) of G. In this paper, we find the maximum and minimum values of the Seidel Estrada index among all graphs with the fixed number of vertices. Our results confirm some conjectures on Seidel Estrada index of graphs that have been posed in [M. Hakimi-Nezhaad, M. Ghorbani, On the Estrada Index of Seidel Matrix, Mathematics Interdisciplinary Research5 (2020) 43–54]. [ABSTRACT FROM AUTHOR]

A graph G is k-edge-Hamiltonian if any collection of vertex-disjoint paths with at most k edges altogether belong to a Hamiltonian cycle in G. A graph G is k-Hamiltonian if for all S ⊆ V (G) with | S | ≤ k , the subgraph induced by V (G) ∖ S has a Hamiltonian cycle. These two concepts are classical extensions of the usual Hamiltonian graphs. In this paper, we present some spectral sufficient conditions for a graph to be k-edge-Hamiltonian and k-Hamiltonian in terms of the adjacency spectral radius as well as the signless Laplacian spectral radius. Our results could be viewed as slight extensions of the recent theorems proved by Li and Ning [Linear Multilinear Algebra. 2016;64:2252–2269], Nikiforov [Czechoslovak Math J. 2016;66:925–940] and Li et al. [Linear Multilinear Algebra. 2018;66:2011–2023]. Moreover, we shall prove a stability result for graphs being k-Hamiltonian, which could be regarded as a complement of two recent results of Füredi et al. [Discrete Math. 2017;340:2688–2690] and [Discrete Math. 2019;342:1919–1923]. [ABSTRACT FROM AUTHOR]

In this paper, we continue the study of Berkani's property (U W Π) introduced in [Berkani M, Kachad M. New Browder and Weyl type theorems. Bull Korean Math Soc. 2015;52:439–452.], in connection with other Weyl-type theorems. Moreover, we give counterexamples to show that some recent results related to this property, which are announced and proved by P. Aiena and M. Kachad in [Aiena P, Kachad M. Property (U W Π) and perturbations. Ann Funct Anal. 2020;11:29–46.] are false. Furthermore, we specify the mistakes committed in each of them and we give the correct versions. We also give a global note on the paper [Jayanthi N, Vasanthakumar P. A new Browder type property. Inter J Math Anal. 2020;14:1–11]. [ABSTRACT FROM AUTHOR]

In this paper, we give the generalization of Cauchy–Binet, Laplace, Sylvester and generalized Dodgson's condensation formulas for the case of rectangular determinants. The proofs are bijective combinatorial proofs similar to that of Zeilberger's paper [Zeilberger D. Dodgson's determinant-evaluation rule proved by TWO-TIMING MEN and WOMEN. Electron J Comb. 1997;4(2):R22; Zeilberger D. A combinatorial approach to matrix algebra. Discrete Math. 1985;56:61–72]. [ABSTRACT FROM AUTHOR]

Let E be the Grassmann algebra of an infinite-dimensional vector space L over a field of characteristic zero. In this paper, we study the Z -gradings on E having the form E = E (r 1 , r 2 , r 3) (v 1 , v 2 , v 3) , in which each element of a basis of L has Z -degree r 1 , r 2 , or r 3 . We provide a criterion for the support of this structure to coincide with a subgroup of the group Z , and we describe the graded identities for the corresponding gradings. We strongly use Elementary Number Theory as a tool, providing an interesting connection between this classical part of Mathematics, and PI Theory. Our results are generalizations of the approach presented in Brandão A, Fidelis C, Guimarães A. Z -gradings of full support on the Grassmann algebra. J Algebra. 2022;601:332–353. DOI:10.1016/j.jalgebra.2022.03.014. See also in arXiv preprint, arXiv:2009.01870v1, 2020]. [ABSTRACT FROM AUTHOR]

The origins of the notion of matchings in groups spawn from a linear algebra problem proposed by E. K. Wakeford [On canonical forms. Proc London Math Soc (2). 1920;18:403–410] which was tackled in Fan and Losonczy [Matchings and canonical forms for symmetric tensors. Adv Math. 1996;117(2):228–238]. In this paper, we first discuss unmatchable subsets in abelian groups. Then we formulate and prove linear analogues of results concerning matchings, along with a conjecture that, if true, would extend the primitive subspace theorem. We discuss the dimension m-intersection property for vector spaces and its connection to matching subspaces in a field extension, and we prove the linear version of an intersection property result of certain subsets of a given set. [ABSTRACT FROM AUTHOR]

The concept of the Drazin inverse of multivalued operators in a Banach space studied by A. Ghorbel and M. Mnif [Monatsh Math. 2019;189:273–293] is generalized in the context of the generalized Drazin inverse of multivalued operators [Rocky Mountain J Math. 2020;50(4):1387–1408]. The purpose of this paper is to present new additive results for this concept. In particular, we give a sufficient condition for an everywhere defined linear relation to have at most one Drazin inverse. Some properties and the explicit expressions for the Drazin inverse of the product are obtained. Also, some results of C. Deng, H. Du [Proc Amer Math Soc. 2006;134:3309–3317] concerning the reduced minimum modulus of Drazin inverses of linear operators on Hilbert spaces are extended to the case of linear relations. [ABSTRACT FROM AUTHOR]

In this paper, we characterize the extremal digraphs with the maximal or minimal α-spectral radius among some digraph classes such as rose digraphs, generalized theta digraphs and tri-ring digraphs with given size m. These digraph classes are denoted by Rmk, ...(m) and ...(m) respectively. The main results about spectral extremal digraph by Guo and Liu [Some results on the spectral radius of generalized ∞ and θ-digraphs. Linear Algebra Appl. 2012;437(9):2200-2208] and Li et al. [The signless Laplacian spectral radius of some strongly connected digraphs. Indian J Pure Appl Math. 2018;49(1):113-127] are generalized to α-spectral graph theory. As a by-product of our main results, an open problem in Li et al. [The signless Laplacian spectral radius of some strongly connected digraphs. Indian J Pure Appl Math. 2018;49(1):113-127] is answered. Furthermore, we determine the digraphs with the first three minimal α-spectral radius among all strongly connected digraphs. Meanwhile, we determine the unique digraph with the fourth minimal α-spectral radius among all strongly connected digraphs for 0 ≤ α ≤ 1/2. [ABSTRACT FROM AUTHOR]

In this paper, we firstly establish new numerical radius inequalities which refine a result of Kittaneh in [Studia Math. 168, 73–80 (2005)], then present some numerical radius inequalities involving non-negative increasing convex functions for n × n operator matrices, which generalize the related results of Shebrawi in [Linear Algebra Appl. 523(15), 1–12 (2017)]. [ABSTRACT FROM AUTHOR]

For a simple graph G, the signless Laplacian matrix of G, denoted by Q(G), is defined as D(G) + A(G), where A(G) and D(G) are the adjacency matrix and the diagonal matrix of vertex degrees of G, respectively. By the smallest signless Laplacian eigenvalue of G, denoted by q′(G), we mean the smallest eigenvalue of Q(G). Let T(n, t) be the Turán graph on n vertices and t parts. In De Lima et al. (The clique number and the smallest Q-eigenvalue of graphs. Discrete Math. 2016;339:1744–1752), the authors posed the following conjecture:Conjecture. Let t ≥ 3 and let n be sufficiently large. If G is a Kt+1-free graph of order n and G ≠ T(n, t), then q′(G) < q′(T(n, t)).In this paper, first we disprove the above conjecture and then pose a new conjecture. [ABSTRACT FROM AUTHOR]

Let p 1 < p 2 < ⋯ < p n be positive numbers, then for any integer m the Loewner matrix associated with the function x m is given by L m = (p i m − p j m) / (p i − p j) i , j = 1 n. A question was left open in a paper [Bhatia R, Friedland S, Jain T. Inertia of loewner matrices. Indiana Univ Math J. 2016;65:1251–1261] by Bhatia, Friedland and Jain to find formulas for the determinants of the matrices L m in the case n = 3. We aim to answer this question firmly in terms of the Schur polynomials in this paper. [ABSTRACT FROM AUTHOR]

In this paper, based on the previous work by Bai [On the convergence of the multisplitting methods for the linear complementarity problem. SIAM J Matrix Anal Appl. 1999;21:67–78] and by Zhang et al. [Improved convergence theorems of multisplitting methods for the linear complementarity problem. Appl Math Comput. 2014;243:982–987], we further discuss the multisplitting AOR (MAOR) method for the linear complementarity problem. Some new convergence conditions of the MAOR method are obtained, which are different from those of the aforementioned papers. [ABSTRACT FROM AUTHOR]

In this paper, based on the previous work by Zhang and Li [The weaker convergence of modulus-based synchronous multisplitting multi-parameters methods for linear complementarity problems, Comput Math Appl. 2014;67:1954–1959], we further discuss the modulus-based synchronous multisplitting multi-parameters AOR (MSMMAOR) method for solving the linear complementarity problems. The new convergence conditions of the MSMMAOR method are obtained, which are weaker than those of the aforementioned paper. [ABSTRACT FROM AUTHOR]

In this paper, the nonlinear matrix equation X p = A # t (M T (X − 1 + B) − 1 M) , where p ≥ 1 is a positive integer, t ∈ [ 0 , 1 ] , M is an n × n nonsingular matrix, A is a positive definite matrix and B is a positive semidefinite matrix, is considered. The notation A # t B is the t-weighted geometric mean of the positive definite matrices A and B. Based on the properties of the Thompson metric, we prove that the nonlinear matrix equation always has a unique positive definite solution and we compare it with the unique positive definite solution of the equation X p = A + M T (X − 1 + B) − 1 M , which has been studied in Jung et al. [On the solution of the nonlinear matrix equation X n = f (X). Linear Algebra Appl. 2009;430:2042–2052]; Meng and Kim [The positive definite solution of the nonlinear matrix equation X p = A + M (B + X − 1 ) − 1 M ∗ . J Comput Appl Math. 2017;322:139–147]. A fixed-point iteration method for obtaining the unique positive definite solution and an elegant estimate of the solution are given. Perturbation analysis of the unique positive definite solution is presented. [ABSTRACT FROM AUTHOR]

In this paper, based on the preconditioners presented by Zhang [A new preconditioner for generalized saddle matrices with highly singular(1,1) blocks. Int J Comput Maths. 2014;91(9):2091-2101], we consider a modified block preconditioner for generalized saddle point matrices whose coefficient matrices have singular (1,1) blocks. Moreover, theoretical analysis gives the eigenvalue distribution, forms of the eigenvectors and the minimal polynomial. Finally, numerical examples show the eigenvalue distribution with the presented preconditioner and confirm our analysis. [ABSTRACT FROM AUTHOR]

This paper deals with a conjecture posed by Abbas Salemi in 2011 (Banach J. Math. Anal.), claiming that for the spectrum of every bounded linear operator on a separable Hilbert space there exists an estimable total decomposition. We partially solve this problem, in the sense that, for the normal operator, there exists an estimable decomposition, under approximately unitary equivalence. [ABSTRACT FROM AUTHOR]

A map that is defined on the set of all symmetric matrices over a field is rank-one nonincreasing if it maps the matrices of rank one to matrices of rank at most one. In the case of the fields with two or three elements nonstandard examples of such additive maps are known to exist. In this paper, all these maps are characterized. Moreover, the existence of nonstandard maps is understood in a geometric sense since they exist precisely in the two cases, where the whole n-dimensional vector space over can be written as a union of two hyperbolic/parabolic quadrics of low indices. This geometric interpretation enables us to realize that these weird examples represent just a tip of an iceberg that appears in an analogous problem on symmetric tensors, where nonstandard maps exist also over larger fields. A few open problems related to the multilinear analog and to homogeneous polynomials are posed. [ABSTRACT FROM AUTHOR]

Let T and S be two self-adjoint positive invertible operators of a complex Hilbert space H. In this paper, we investigate some inequalities involving the quadratic forms of the weighted arithmetic and harmonic means of T and S. Application for operator entropies is also discussed. [ABSTRACT FROM AUTHOR]

In this paper, we present the necessary and sufficient conditions for which the given pair of closed subspaces has a pair of non-trivial principal invariant subspaces. Using this we show that every pairof closed subspaces withorhas a pair of non-trivial principal invariant subspaces. Also we prove that the pairof closed subspaces withhas a pair of non-trivial principal invariant subspaces if and only ifSimilar results are proved for non-degenerate principal invariant subspaces. [ABSTRACT FROM PUBLISHER]

Letbe the algebra of allreal matrices. Anreal matrixis even doubly stochastic if it is a convex combination of even permutation matrices. For,is said to be even majorized by(written as), if there exists an even doubly stochastic matrixsuch that. In this paper, the concept of even majorization is investigated and then the linear preservers and strong linear preservers of this concept are characterized on. [ABSTRACT FROM PUBLISHER]

A matrixover a field is minimal if for every matrixthat commutes with, the centralizer ofis a subset of the centralizer of. In this paper, we study the minimal matrices over the field with two elements. We characterize the minimal matrices with their minimal polynomial of the form, whereis an irreducible polynomial and. We also characterize all minimal matrices with spectrum in. [ABSTRACT FROM AUTHOR]