关于谢邦杰的一个定理的推广

本文采用[1]的术语.1978年,谢邦杰将著名的Hadamard不等式推广到四元数体上,即:设A=(a_ij)_n×n为四元数体上可中心化的非奇异矩阵,则等号成立当且仅当A的各行广义正交.本文给出关于四元数体上长方阵的不等式(2).当m=n,且A是可中心化的非奇异矩阵时,(2)式即为(1)式.     

由本性随机阵导致的陈代数

A matrix of order n whose row sums are all equal to 1 is called an essentially stochastic matrix (see Johnsen [4]). We extend this notion as the following. Let F be a field of characteristic 0 or a prime greater than n. M_n(F) denotes the set of all n×n matrices over F. Let t be an elernent of F. A matrix A=(a_ij) in M_n(F) is called essentially t-stochastic' provided its row sums are each equal to t. We denote by R_n(t) the set of all essentially t-stochastic matrices over F. We shall mainly study R_n(0) and R_n(F)=(?)R_n(t). Our main references are Johnson [2,4] and Kim [5].     

Pivot size in gaussian elimination

LetA = (a _ij ) be a real n x n matrix such that |a _ij | < 1. It has been conjectured by WILKINSON that if the process of Gaussian elimination with complete pivoting is applied to A then all the pivots are less than or equal to n in absolute value. This conjecture is proved forn=4.Sponsored by the Mathematics Research Center, United States Army, Madison, Wisconsin, under Contract No.: DA-31-124-ARO-D-462.     

Enumeration of finite topologies

Let T₀(n) be the number of marked topologies satisfying the separation axiom T₀ that can be imposed on a finite set of n elements. In this paper the formula $$T_0 \left( n \right) = \Sigma \frac{{n!}}{{p_1 !...p_m !}}V\left( {p_1 , ..., p_m } \right)$$ is obtained, where the summation extends over all ordered sets of natural numbers (p₁, ..., p_m) such that p₁+...+p_m=n, and V(p₁, ..., p_m) denotes the number of matrices σ=(σ_ij) of ordern with the following properties: 1) each of the entries σ_ij is either 0 or 1, and if σ_ij=1 andσ_ij=1, then σ_ij=1;2) if the matrix σ is partitioned into blocks of sizes p_ixp_j, then all blocks under the main diagonal are zero, all diagonal blocks are identity matrices, and in each column of any block situated above the main diagonal at least one entry is 1. Some properties of the values V(p₁, ..., p_m)are obtained; in particular, it is shown that all these values are odd. Formulas are obtained for V(P₁, ..., p_m) corresponding to the simplest sets (p₁, ..., P_m) needed to calculate T₀(n) for n?8 (without using a computer).     

Certain complexes associated to a sequence and a matrix

Let R be a commutative noetherian ring with unit. To a sequencex:=x₁,...,x_n of elements of R and an m-by-n matrix α:=(α_ij) with entries in R we assign a complex D*(x;α), in case that m=n or m=n?1. These complexes will provide us in certain cases with explicit minimal free resolutions of ideals, which are generated by the elements a_i:=∑α_ijx_j and the maximal minors of α.     

Interrelations between eigenvalues and diagonal entries of Hermitian matrices implying their block diagonality

Let A=(a_ij) _i,j ⁿ =1 be a Hermitian matrix and let denote its eigenvalues. If , k<n, then A is known to be block diagonal. We show that this result easily follows from the Cauchy interlacing theorem, generalize it by introducing a convex strictly monotone function f(t), and prove that in the positivedefinite case, the matrix diagonal entries can be replaced by the diagonal entries of a Schur complement. Bibliography: 4 titles. Translated fromZapiski Nauchnykh Seminarov POMI, Vol. 229, 1995, pp. 153–158. Translated by L. Yu. Kolotilina.     

Inclusion sets for the singular values of a square matrix

The paper presents a general approach to deriving inclusion sets for the singular values of a matrix A = (a_ij) ∈ ℂ ^n×n. The key to the approach is the following result: If σ is a singular value of A, then a certain matrix C(σ, A) of order 2n, whose diagonal entries are σ² − | a_ii|², i = 1, …, n, is singular. Based on this result, we use known diagonal-dominance type nonsingularity conditions to obtain inclusion sets for the singular values of A. Scaled versions of the inclusion sets, allowing one, in particular, to obtain Ky Fan type results for the singular values, are derived by passing to the conjugated matrix D⁻¹C(σ, A)D, where D is a positive-definite diagonal matrix. Bibliography: 16 titles. Translated from Zapiski Nauchnykh Seminarov POMI, Vol. 359, 2008, pp. 52–77.     

亚纯函数在角域内的波莱耳方向

Suppose that f(z) is a meromorphic function of order λ(0<λ≤∞) and of lower order μ(0≤μ<∞) in the plane. Let ρ(μ≤ρ≤λ) be a finite positive number. B: arg z=θ₀(0≤θ₀ <2π) is called a Borel direction of order ρ of f(z), if for any complex number a, the equality holds, except at most for some a belonging to a set of linear measure zero. For the exceptional values a, we have ρ(θ₀, a)>ρ, except two possible values. With the above hypotheses on f(z), λ, μ and ρ, We have the following lemmas. Lemma 1. There exists a sequence of positive numbers (r_n) such that(?)=∞ and that Lemma 2. If f(z) has a deficient value a₀ with deficiency δ(a₀, f), then we have where (r_n) is the sequence defined in the Lemma 1 and when a_0=∞, we have to replace(?)by (?) in the left hand side of (*). Lemma 3. Suppose that B_1 : arg z =θ₁ and B₂ : arg z=θ₂ (0≤θ₁<θ₂<2π+θ₁) are two half straight lines from the origin and there are no Borel directions of order≥ρ(ρ>1/2) of f(z) in θ₁₀, the inequality holds as n is sufficiently large, where K₁ is a positive number not depending on n andεand when a₀=∞, it is necessary to replace we have θ₂-θ₁≤π/ρ. Theorem 1. Suppose that f(z) is a meromorphic function of order λ (1/2<λ≤+∞) and of lower order μ(0≤μ<+∞) in the plane. Let p be a number such that μ≤ρ≤λ and that 1/2<ρ<+∞If f~((k))(z) has p(1≤P<+∞) deficient values a_i (i=1,2,…,p) with deficiencies δ(a_i,f^(k)), then f(z) has a Borel direction of order ≥ρ in any angular domain, the magnitude of which is larger than It is convenient to consider Julia directions as Borel directions of order zero.Under this assumption, We have the following. Theorem 2. Suppose that f(z) is a meromorphic function of order λ and of finite lower order μ in the plane and that ρ(μ≤ρ≤λ) is a finite number. If p denotes the number of deficient values of f(z) and q denotes the number of Borel directions of order ≥p of f(z), then we have p≤q.     

The generalized Eckart-Young principal axis theorem

A rectangular matrix [a_pq ] is said to be diagonal if a_pq = 0 when p ≠ q. We present a simple proof of the following theorem of Wiegmann, but in principle given earlier by Eckart and Young: THEOREM If {A_i) is a set of complex r – s matrices such thatA A andA A are Hermitian for all i andj, then there exist unitary matrices P and Q such that for each i the matrixpA Q is real and diagonal Special cases of the above are well known and extremely useful. For example, the case n = 1 yields the classical singular value decomposition.     

Doubly stochastic graph matrices,II

If G is a graph on n vertices, its Laplacian matrix L(G) = D(G) - A(G) is the difference of the diagonal matrix of vertex degrees and the adjacency matrix. The main purpose of this note is to continue the study of the positive definite, doubly stochastic graph matrix (I_n + L(G))?¹= ω(G) = (w_ij). If, for example, w(G) = min w_ij, then w(G)≥0 with equality if and only if G is disconnected and w(G) ≤ l/(n + 1) with equality if and only if G = K_n. If i¦j, then w_ii ≥2wij, with equality if and only if the ith vertex has degree n - 1. In a sense made precise in the note, max w,, identifies most remote vertices of G. Relations between these new graph invariants and the algebraic connectivity emerge naturally from the fact that the second largest eigenvalue of ω(G) is 1/(1 + a(G)).