Kernels of digraphs with finitely many ends

According to Richardson’s theorem, every digraph $G$ without directed odd cycles that is either (a) locally finite or (b) rayless has a kernel (an independent subset $K$ with an incoming edge from every vertex in $G?K$). We generalize this theorem showing that a digraph without directed odd cycles has a kernel when (a) for each vertex, there is a finite set separating it from all rays, or (b) each ray contains at most finitely many vertices dominating it (having an infinite fan to the ray) and the digraph has finitely many ends. The restriction to finitely many ends in (b) can be weakened, admitting infinitely many ends with a specific structure, but the possibility of dropping it remains a conjecture.     

A structural characterization of real k-potent matrices

Some well-known characterizations of nonnegative k-potent matrices have been obtained by Flor [P. Flor, On groups of nonnegative matrices, Compositio Math. 21 (1969), pp. 376–382.] and Jeter and Pye [M. Jeter and W. Pye, Nonnegative (s,?t)-potent matrices, Linear Algebra Appl. 45 (1982), pp. 109–121.]. In this article, we obtain a structural characterization of a real k-potent matrix A, provided that (sgn(A)) ^k+1 is unambiguously defined, regardless of whether A is nonnegative or not.     

Asymptotic properties of the moment convergence for NA sequences

It is well-known that the complete convergence theorem for i.i.d. random variables has been an active topic since the famous work done by Hsu and Robbins [6]. Chow [4] obtained a moment version of Hsu and Robbins series. However, the series tends to infinity whenever ε goes to zero, so it is of interest to investigate the asymptotic behavior of the series as ε goes to zero. This note gives some limit theorems of the series generated by moments for NA random variables.     

Spectra of periodic operator polynomials with finitely many diagonals

Spectra of polynomials whose coefficients are periodic operators with finitely many nonzero diagonals are studied. Such polynomials appear in the study of infinite chains of damped harmonic oscillators. It is proved that, assuming the spectrum is bounded, it consists of finitely many analytic arcs. Criteria for existence of point spectrum are given. Several important particular cases are indicated.     

Hankel determinants of some polynomials arising in combinatorial analysis

In this paper we investigate Hankel determinants of the form , where c _n (t) is one of a number of polynomials of combinatorial interest. We show how some results due to Radoux may be generalized, and also show how “stepped up” Hankel determinants of the form may be evaluated. This revised version was published online in June 2006 with corrections to the Cover Date.     

Solution of the Karlin problem for zero-diminishing sequences satisfying a Carleman condition

We describe all zero-diminishing sequences (over the real-valued polynomials on ) which additionally satisfy a Carleman condition and show that they are of the same kind as those in E. Laguerre's theorem from 1884.

     

Binary caps with many free pairs of points

We introduce the following new viewpoint in the study of caps in PG(m,q). The objective is to maximize, among all caps of given cardinality in a given projective space, the number of free pairs of points, which we define as pairs of points not participating in any coplanar quadruple of points of the cap. We survey the known results (which were motivated by an application in statistical experiment design) and then we improve the known lower bound on the number of free pairs of points for q = 2 and the smallest cap sizes for which the maximization problem is non‐trivial. © 2006 Wiley Periodicals, Inc. J Combin Designs 14: 490–499, 2006     

Bounding the inefficiency of Nash equilibria in games with finitely many players

This paper derives bounds on the gap between optimal performance and the performance of Nash equilibria in n-person games with continuous action sets. Specific interesting expressions are obtained for the average efficiency per player in congestion games.     

A moment approach to analyze zeros of triangular polynomial sets

Let be a zero-dimensional ideal of such that its associated set of polynomial equations for all is in triangular form. By introducing multivariate Newton sums we provide a numerical characterization of polynomials in . We also provide a necessary and sufficient (numerical) condition for all the zeros of to be in a given set , without explicitly computing the zeros. In addition, we also provide a necessary and sufficient condition on the coefficients of the 's for to have (a) only real zeros, (b) to have only real zeros, all contained in a given semi-algebraic set . In the proof technique, we use a deep result of Curto and Fialkow (2000) on the -moment problem, and the conditions we provide are given in terms of positive definiteness of some related moment and localizing matrices depending on the 's via the Newton sums of . In addition, the number of distinct real zeros is shown to be the maximal rank of a related moment matrix.

     

Precise rates of the first moment convergence in the LIL for NA sequences

Let be a strictly stationary sequence of negatively associated random variables with zero mean and finite variance. We set and , . If , then for any , we show the precise rates of the first moment convergence in the law of the iterated logarithm for a kind of weighted infinite series of and as , and as .     

不同分布NA序列的对数律

通过适当的改变矩条件，把同分布NA随机变量序列部分和的对数律从本质上推广到不同分布，全面改进了梁汉营和苏淳1998年的结果．并在此基础上得到不同分布NA序列随机足标和的对数律．     

A note on properties of locally finitely convergent sequences with respect to median filter

Let F_k be a mapping from R^Z to R^Z, satisfying that for x∈R^Z and n∈Z, F_k(x)(n) is the (k+1)th largest value (median value) of the 2k+1 numbers x(n−k),…,x(n),…,x(n+k). In [3] [W.Z. Ye, L. Wang, L.G. Xu, Properties of locally convergent sequences with respect to median filter, Discrete Mathematics 309 (2009) 2775–2781], we conjectured that for k∈{2,3}, if there exists n₀∈Z such that x is locally finitely convergent with respect to F_k on {n₀,…,n₀+k−1}, then x is finitely convergent with respect to F_k. In this paper, we obtain some sufficient conditions for a sequence finitely converging with respect to median filters. Based on these results, we prove that the conjecture is true.     

A moment problem and a family of integral evaluations

We study the Al-Salam-Chihara polynomials when . Several solutions of the associated moment problem are found, and the orthogonality relations lead to explicit evaluations of several integrals. The polynomials are shown to have raising and lowering operators and a second order operator equation of Sturm-Liouville type whose eigenvalues are found explicitly. We also derive new measures with respect to which the Ismail-Masson system of rational functions is biorthogonal. An integral representation of the right inverse of a divided difference operator is also obtained.

     

A topological characterization of the existence of fixed points and applications

We prove a topological two‐way characterization of the existence of fixed‐points, without using linear or convexity structures and provide applications in optimization‐related problems. Such a characterization is also demonstrated for a fixed‐component point, a slight generalization of a fixed point.     

Representation of measures with polynomial denseness in , , and its application to determinate moment problems

It has been proved that algebraic polynomials are dense in the space , , iff the measure is representable as with a finite non-negative Borel measure and an upper semi-continuous function such that is a dense subset of the space    as equipped with the seminorm . The similar representation ( ) with the same and ( , and is also a dense

subset of ) corresponds to all those measures (supported by ) that are uniquely determined by their moments on ( ). The proof is based on de Branges' theorem (1959) on weighted polynomial approximation. A more general question on polynomial denseness in a separable Fréchet space in the sense of Banach has also been examined.

     

The utilization of total mass to determine the switching points in the symmetric boundary control problem with a linear reaction term

The authors study the problem , and u(0,t)=u(1,t)=ψ(t), where ψ(t)=u₀ for t2k<t<t2k+1 and ψ(t)=0 for , with t₀=0 and the sequence tk is determined by the equations , for , and , for k=2,4,6,… and where 0<m<M. Note that the switching points , are unknown. Existence and uniqueness are demonstrated. Theoretical estimates of the tk and tk+1−tk are obtained and numerical verifications of the estimates are presented. The case of ux(0,t)=ux(1,t)=ψ(t) is also considered and analyzed.     

A Hausdorff‐like moment problem and the inversion of the Laplace transform

We consider the problem of finding u ∈ L ²(I ), I = (0, 1), satisfying ∫_I u (x )x dx = μ _k , where k = 0, 1, 2, …, (α _k ) is a sequence of distinct real numbers greater than –1/2, and μ = (μ _kl ) is a given bounded sequence of real numbers. This is an ill‐posed problem. We shall regularize the problem by finite moments and then, apply the result to reconstruct a function on (0, +∞) from a sequence of values of its Laplace transforms. Error estimates are given. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)