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1.
Let
F(x) = k=onnkAkxk
An ≠ 0,
and
G(x) = k=onnkBkxk
Bn ≠ 0,
be polynomials with real zeros satisfying An?1 = Bn?1 = 0, and let
H(x) = k=on-2nkAkBkxk.
Using the recently proved validity of the van der Waerden conjecture on permanents, some results on the real zeros of H(x) are obtained. These results are related to classical results on composite polynomials.  相似文献   

2.
Asymptotic results are obtained for pA(k)(n), the kth difference of the function pA(n) which is the number of partitions of n into integers from A. Under certain restrictions on A it is shown that
PA(k+1)(n)PA(k)(n) = O(n?1/2) (n→ ∫)
thereby verifying for these A a conjecture of Bateman and Erdös.  相似文献   

3.
It is proved that Wigner's semicircle law for the distribution of eigenvalues of random matrices, which is important in the statistical theory of energy levels of heavy nuclei, possesses the following completely deterministic version. Let An=(aij), 1?i, ?n, be the nth section of an infinite Hermitian matrix, {λ(n)}1?k?n its eigenvalues, and {uk(n)}1?k?n the corresponding (orthonormalized column) eigenvectors. Let v1n=(an1,an2,?,an,n?1), put
Xn(t)=[n(n-1)]-12k=1[(n-1)t]|vn1uf(n-1)|2,0?t?1
(bookeeping function for the length of the projections of the new row v1n of An onto the eigenvectors of the preceding matrix An?1), and let finally
Fn(x)=n-1(number of λk(n)?xn,1?k?n)
(empirical distribution function of the eigenvalues of Ann. Suppose (i) limnannn=0, (ii) limnXn(t)=Ct(0<C<∞,0?t?1). Then
Fn?W(·,C)(n→∞)
,where W is absolutely continuous with (semicircle) density
w(x,C)=(2Cπ)-1(4C-x212for|x|?2C0for|x|?2C
  相似文献   

4.
For an n × n Hermitean matrix A with eigenvalues λ1, …, λn the eigenvalue-distribution is defined by G(x, A) := 1n · number {λi: λi ? x} for all real x. Let An for n = 1, 2, … be an n × n matrix, whose entries aik are for i, k = 1, …, n independent complex random variables on a probability space (Ω, R, p) with the same distribution Fa. Suppose that all moments E | a | k, k = 1, 2, … are finite, Ea=0 and E | a | 2. Let
M(A)=σ=1s θσPσ(A,A1)
with complex numbers θσ and finite products Pσ of factors A and A1 (= Hermitean conjugate) be a function which assigns to each matrix A an Hermitean matrix M(A). The following limit theorem is proved: There exists a distribution function G0(x) = G1x) + G2(x), where G1 is a step function and G2 is absolutely continuous, such that with probability 1 G(x, M(Ann12)) converges to G0(x) as n → ∞ for all continuity points x of G0. The density g of G2 vanishes outside a finite interval. There are only finitely many jumps of G1. Both, G1 and G2, can explicitly be expressed by means of a certain algebraic function f, which is determined by equations, which can easily be derived from the special form of M(A). This result is analogous to Wigner's semicircle theorem for symmetric random matrices (E. P. Wigner, Random matrices in physics, SIAM Review9 (1967), 1–23). The examples ArA1r, Ar + A1r, ArA1r ± A1rAr, r = 1, 2, …, are discussed in more detail. Some inequalities for random matrices are derived. It turns out that with probability 1 the sharpened form
lim supn→∞i=1ni(n)|2?6An62? 0.8228…
of Schur's inequality for the eigenvalues λi(n) of An holds. Consequently random matrices do not tend to be normal matrices for large n.  相似文献   

5.
Let Ω = {1, 0} and for each integer n ≥ 1 let Ωn = Ω × Ω × … × Ω (n-tuple) and Ωnk = {(a1, a2, …, an)|(a1, a2, … , an) ? Ωnand Σi=1nai = k} for all k = 0,1,…,n. Let {Ym}m≥1 be a sequence of i.i.d. random variables such that P(Y1 = 0) = P(Y1 = 1) = 12. For each A in Ωn, let TA be the first occurrence time of A with respect to the stochastic process {Ym}m≥1. R. Chen and A.Zame (1979, J. Multivariate Anal. 9, 150–157) prove that if n ≥ 3, then for each element A in Ωn, there is an element B in Ωn such that the probability that TB is less than TA is greater than 12. This result is sharpened as follows: (I) for n ≥ 4 and 1 ≤ kn ? 1, each element A in Ωnk, there is an element B also in Ωnk such that the probability that TB is less than TA is greater than 12; (II) for n ≥ 4 and 1 ≤ kn ? 1, each element A = (a1, a2,…,an) in Ωnk, there is an element C also in Ωnk such that the probability that TA is less than TC is greater than 12 if n ≠ 2m or n = 2m but ai = ai + 1 for some 1 ≤ in?1. These new results provide us with a better and deeper understanding of the fair coin tossing process.  相似文献   

6.
Let fk(n) denote the maximum of k-subsets of an n-set satisfying the condition in the title. It is proven that f2t ? 1(n) ? f2t(n + 1) ? (tn)(t2t?1) with equalities holding iff there exists a Steiner-system S(t, 2t ? 1, n). The bounds are approximately best possile for k ? 6 and of correct order of magnitude for k >/ 7, as well, even if the corresponding Steiner-systems do not exist.Exponential lower and upper bounds are obtained for the case if we do not put size restrictions on the members of the family (i.e., the nonuniform case).  相似文献   

7.
Let V be a set of n points in Rk. Let d(V) denote the diameter of V, and l(V) denote the length of the shortest circuit which passes through all the points of V. (Such a circuit is an “optimal TSP circuit”.) lk(n) are the extremal values of l(V) defined by lk(n)=max{l(V)|VVnk}, where Vnk={V|V?Rk,|V|=n, d(V)=1}. A set VVnk is “longest” if l(V)=lk(n). In this paper, first some geometrical properties of longest sets in R2 are studied which are used to obtain l2(n) for small n′s, and then asymptotic bounds on lk(n) are derived. Let δ(V) denote the minimal distance between a pair of points in V, and let: δk(n)=max{δ(V)|VVnk}. It is easily observed that δk(n)=O(n?1k). Hence, ck=lim supn→∞δk(n)n1k exists. It is shown that for all n, ckn?1k≤δk(n), and hence, for all n, lk(n)≥ ckn1?1k. For k=2, this implies that l2(n)≥(π212)14n12, which generalizes an observation of Fejes-Toth that limn→∞l2(n)n?12≥(π212)14. It is also shown that lk(n) ≤ [(3?√3)k(k?1)]nδk(n) + o(n1?1k) ≤ [(3?√3)k(k?1)]n1?1k + o(n1?1k). The above upper bound is used to improve related results on longest sets in k-dimensional unit cubes obtained by Few (Mathematika2 (1955), 141–144) for almost all k′s. For k=2, Few's technique is used to show that l2(n)≤(πn2)12 + O(1).  相似文献   

8.
Suppose A, D1,…,Dm are n × n matrices where A is self-adjoint, and let X = Σmk = 1DkAD1k. It is shown that if ΣDkD1k = ΣD1kDk = I, then the spectrum of X is majorized by the spectrum of A. In general, without assuming any condition on D1,…,Dm, a result is obtained in terms of weak majorization. If each Dk is a diagonal matrix, then X is equal to the Schur (entrywise) product of A with a positive semidefinite matrix. Thus the results are applicable to spectra of Schur products of positive semidefinite matrices. If A, B are self-adjoint with B positive semidefinite and if bii = 1 for each i, it follows that the spectrum of the Schur product of A and B is majorized by that of A. A stronger version of a conjecture due to Marshall and Olkin is also proved.  相似文献   

9.
Let S be a Dirichlet form in L2(Ω; m), where Ω is an open subset of Rn, n ? 2, and m a Radon measure on Ω; for each integer k with 1 ? k < n, let Sk be a Dirichlet form on some k-dimensional submanifold Ωk of Ω. The paper is devoted to the study of the closability of the forms E with domain C0(Ω) and defined by: (?,g)=E(?, g)+ ip=1Eki(?ki, gki) where 1 ? kp < ? < n, and where ?ki, gki denote restrictions of ?, g in C0(Ω) to Ωki. Conditions are given for E to be closable if, for each i = 1,…, p, one has ki = n ? i. Other conditions are given for E to be nonclosable if, for some i, ki < n ? i.  相似文献   

10.
In this paper, we establish the following results: Let A be a square matrix of rank r. Then (a) (A+A1)2 is idempotent of rank r, and trrA (defined as the sum of the principal minors of order r in A) is one iff A is Hermitian idempotent. (b) As=At for some positive integers st, and trA=rankA iff A is idempotent. (c) A(A1A)s= A(AA1)t for some integers st iff AA1=A1A is idempotent, while A(A1A)s= A(AA1)s for some integers s≠0 iff AA1=A1A. (d) A(A1A)s=A1 (AA1)t for some integers st and rankA=trA iff A is Hermitian idempotent, while A(A1A)s= A1(AA1)s for some integer s iff A is Hermitian. Here A1 indicates the conjugate transpose of A, and P-α is defined iff (P+)α=(Pα)+ for all positive integers α and P+ is the Moore-Penrose inverse of P.  相似文献   

11.
12.
Let θ(k, pn) be the least s such that the congruence x1k + ? + xsk ≡ 0 (mod pn) has a nontrivial solution. It is shown that if k is sufficiently large and divisible by p but not by p ? 1, then θ(k, pn) ≤ k12. We also obtain the average order of θ(k), the least s such that the above congruence has a nontrivial solution for every prime p and every positive integer n.  相似文献   

13.
The permanent function is used to determine geometrical properties of the set Ωn of all n × n nonnegative doubly stochastic matrices. If F is a face of Ωn, then F corresponds to an n × n (0, 1)-matrix A, where the permanent of A is the number of vertices of F. If A is fully indecomposable, then the dimension of F equals σ(A) ? 2n + 1, where σ(A) is the number of 1's in A. The only two-dimensional faces of Ωn are triangles and rectangles. For n ? 6, Ωn has four types of three-dimensional faces. The facets of the faces of Ωn are characterized. Faces of Ωn which are simplices are determined. If F is a face of Ωn which is two-neighborly but not a simplex, then F has dimension 4 and six vertices. All k-dimensional faces with k + 2 vertices are determined. The maximum number of vertices of a k-dimensional face is 2k. All k-dimensional faces with at least 2k?1 + 1 vertices are determined.  相似文献   

14.
Let Ω denote a connected and open subset of Rn. The existence of n commuting self-adjoint operators H1,…, Hn on L2(Ω) such that each Hj is an extension of i∂∂xj (acting on Cc(Ω)) is shown to be equivalent to the existence of a measure μ on Rn such that f → \̂tf (the Fourier transform of f) is unitary from L2(Ω) onto Ω. It is shown that the support of μ can be chosen as a subgroup of Rn iff H1,…, Hn can be chosen such that the unitary groups generated by H1,…, Hn act multiplicatively on L2(Ω). This happens iff Ω (after correction by a null set) forms a system of representatives for the quotient of Rn by some subgroup, i.e., iff Ω is essentially a fundamental domain.  相似文献   

15.
It is shown that if A?Ωn?{Jn} satisfies
nkσk(A)?(n?k+1)2 σk?1(A)
(k=1,2,…,n)
, where σk(A) denotes the sum of all kth order subpermanent of A, then Per[λJn+(1?λ)A] is strictly decreasing in the interval 0<λ<1.  相似文献   

16.
Let a complex pxn matrix A be partitioned as A′=(A1,A2,…,Ak). Denote by ?(A), A′, and A? respectively the rank of A, the transpose of A, and an inner inverse (or a g-inverse) of A. Let A(14) be an inner inverse of A such that A(14)A is a Hermitian matrix. Let B=(A(14)1,A(14)2,…,Ak(14)) and ρ(A)=i=1kρ(Ai).Then the product of nonzero eigenvalues of BA (or AB) cannot exceed one, and the product of nonzero eigenvalues of BA is equal to one if and only if either B=A(14) or Ai>Aj1=0 for all ij,i, j=1,2,…,k . The results of Lavoie (1980) and Styan (1981) are obtained as particular cases. A result is obtained for k=2 when the condition ρ(A)=i=1kρ(Ai) is no longer true.  相似文献   

17.
Let Fn denote the ring of n×n matrices over the finite field F=GF(q) and let A(x)=ANxN+ ?+ A1x+A0?Fn[x]. A function ?:Fn→Fn is called a right polynomial function iff there exists an A(x)?Fn[x] such that ?(B)=ANBN+?+A1B+ A0 for every B?Fn. This paper obtains unique representations for and determines the number of right polynomial functions.  相似文献   

18.
The Schur product of two n×n complex matrices A=(aij), B=(bij) is defined by A°B=(aijbij. By a result of Schur [2], the algebra of n×n matrices with Schur product and the usual addition is a commutative Banach algebra under the operator norm (the norm of the operator defined on Cn by the matrix). For a fixed matrix A, the norm of the operator B?A°B on this Banach algebra is called the Schur multiplier norm of A, and is denoted by ∥Am. It is proved here that ∥A∥=∥U1AU∥m for all unitary U (where ∥·∥ denotes the operator norm) iff A is a scalar multiple of a unitary matrix; and that ∥Am=∥A∥ iff there exist two permutations P, Q, a p×p (1?p?n) unitary U, an (n?p)×(n?p)1 contraction C, and a nonnegative number λ such that
A=λPU00CQ;
and this is so iff ∥A°A?∥=∥A∥2, where ā is the matrix obtained by taking entrywise conjugates of A.  相似文献   

19.
Let A be the Clifford algebra constructed over a quadratic n-dimensional real vector space with orthogonal basis {e1,…, en}, and e0 be the identity of A. Furthermore, let Mk(Ω;A) be the set of A-valued functions defined in an open subset Ω of Rm+1 (1 ? m ? n) which satisfy Dkf = 0 in Ω, where D is the generalized Cauchy-Riemann operator D = ∑i = 0m ei(??xi) and k? N. The aim of this paper is to characterize the dual and bidual of Mk(Ω;A). It is proved that, if Mk(Ω;A) is provided with the topology of uniform compact convergence, then its strong dual is topologically isomorphic to an inductive limit space of Fréchet modules, which in its turn admits Mk(Ω;A) as its dual. In this way, classical results about the spaces of holomorphic functions and analytic functionals are generalized.  相似文献   

20.
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