共查询到20条相似文献,搜索用时 31 毫秒
1.
Saharon Shelah 《Discrete Mathematics》2009,309(8):2349-1352
Suppose we are given a family of choice functions on pairs from a given finite set (with at least three elements) closed under permutations of the given set. The set is considered the set of alternatives (say candidates for an office). The question is, what are the choice functions c on pairs of this set of the following form: for some (finite) family of “voters”, each having a preference, i.e. a choice from each pair from the given family, is chosen by the preference of the majority of voters. We give full characterization. 相似文献
2.
D. Castro M. Giusti J. Heintz G. Matera L.M. Pardo 《Foundations of Computational Mathematics》2003,3(4):347-420
Elimination theory was at the origin of algebraic geometry in the nineteenth century and now deals with the algorithmic solving of multivariate polynomial equation systems over the complex numbers or, more generally, over an arbitrary algebraically closed field. In this paper we investigate the intrinsic sequential time complexity of universal elimination procedures for arbitrary continuous data structures encoding input and output objects of elimination theory (i.e., polynomial equation systems) and admitting the representation of certain limit objects. Our main result is the following: let there be given such a data structure and together with this data structure a universal elimination algorithm, say P, solving arbitrary
parametric polynomial equation systems. Suppose that the algorithm P avoids unnecessary branchings and that
P admits the efficient computation of certain natural limit objects (as, e.g., the Zariski closure of a given constructible algebraic set or the parametric greatest common divisor of two given algebraic families of univariate polynomials). Then P$ cannot be a polynomial time algorithm. The paper contains different variants of this result and discusses their practical implications. 相似文献
3.
N. A. Davydov 《Ukrainian Mathematical Journal》1991,43(4):388-391
Suppose a closed unbounded set F Rn is a union of a finite number p of closed unbounded sets Fi that are pairwise disjoint, and suppose f is a continuous mapping of F into the metric space R(2). With each set Fi there is associated a point at infinity i, at which it is assumed that f has a finite limit Ai R(2), i=1, 2, ..., p. It is proved that: 1) f is bounded on F; 2) if f is a real functional, then the set
contains a smallest and a largest value; 3) if the distance between Fi and Fj is greater than zero whenever i j, then f is uniformly continuous on F.Translated from Ukrainskii Matematicheskii Zhurnal, Vol. 43, No. 3, pp. 422–427, March, 1991. 相似文献
4.
Warren B. Moors 《Topology and its Applications》2007,154(2):428-433
In this paper we prove a theorem more general than the following. Suppose that X is ?ech-complete and Y is a closed subset of a product of a separable metric space with a compact Hausdorff space. Then for each separately continuous function there exists a residual set R in X such that f is jointly continuous at each point of R×Y. This confirms the suspicions of S. Mercourakis and S. Negrepontis from 1991. 相似文献
5.
S Coene A Arnout F C R Spieksma 《The Journal of the Operational Research Society》2010,61(12):1719-1728
This paper deals with a study on a variant of the Periodic Vehicle Routing Problem (PVRP). As in the traditional Vehicle Routing Problem, customer locations each with a certain daily demand are given, as well as a set of capacitated vehicles. In addition, the PVRP has a horizon, say T days, and there is a frequency for each customer stating how often within this T-day period this customer must be visited. A solution to the PVRP consists of T sets of routes that jointly satisfy the demand constraints and the frequency constraints. The objective is to minimize the sum of the costs of all routes over the planning horizon. We develop different algorithms solving the instances of the case studied. Using these algorithms we are able to realize considerable cost reductions compared to the current situation. 相似文献
6.
1.IntroductionConsiderthemodelY=X"0 g(T) E,(1'1)whereX"~(xl,',xo)areexplanatoryvariablesthatenterlinearly,Pisakx1vectorofunknownparameters,Tisanotherexplanatoryvariablesthatentersinanonlinearfashion,g')isanunknownsmoothfunctionofTinR',(X,T)andeareindependent,andeistheerrorwithmean0andvariancea2.Trangesoveranondegeneratecompact1-dimensionalilltervalC*;withoutlossofgenerality,C*=[0,1].Chenl2]discussedasymptoticnormalityofestimatorsP.of0byusingpiecewisepolynthacaltoapproximateg.Speckmanls… 相似文献
7.
8.
Marco Longinetti 《Geometriae Dedicata》1986,20(1):27-41
Suppose that two distinct plane convex bodies have the same Steiner symmetrals about a finite number n of given lines. Then we obtain an upper bound for the measure of their symmetric difference. The bound is attained if, and only if, the directions of the lines are equally spaced and the bodies are two regular concentric polygons, with n sides, each obtained from the other by rotation through an angle /n. This result follows from a new isoperimetric inequality for convex polygons. 相似文献
9.
U. B. Darji 《Acta Mathematica Hungarica》1999,83(1-2):97-106
Suppose {Mn} is a sequence of pairwise disjoint, nowhere dense closed subsets of [0, 1] and {Fn} is a sequence of continuous functions. We show that there exists a continuous function F which has the same derivate structure as Fn at each point of Mn. In addition, F can be made BV if n=1 V(Fn, Mn), the sum of the variation of Fn|Mn, is finite. A well-known and very useful theorem of Laczkovich and Petruska as well as many classical examples follow readily from our results. 相似文献
10.
Yu Xiangming 《数学学报(英文版)》1990,6(3):220-229
Suppose thatf(x)C[–1, 1],f(x) is convex in [0,1] and concave in [–1,0] with the new concept of regular convexity-turning points,we obtain the following estimates of Jackson type for coconvex approximation off(x) by algebraic polynomials of degree n:
相似文献
11.
P. V. Galkin 《Mathematical Notes》1974,15(1):3-8
Suppose that on the Interval [a, b] the nodes $$a = x_0< x_1< \ldots< x_m< x_{m + 1} = b$$ are given and the functions u0(t)=ω0(t) $$u_i (t) = \omega _0 (t)\smallint _0^t \omega _1 (\varepsilon _1 )d\varepsilon _1 \ldots \smallint _a^{\varepsilon _{\iota - 1} } \omega _1 (\varepsilon _1 )d\varepsilon _\iota ,\varepsilon _0 = t(i = 1,2, \ldots ,n)$$ where the functions ωi(t)> 0 have continuous (n?i)-th derivatives (i=0, 1, ..., n). Sn,m will designate the subspace of functions that have continuous (n?1)-st derivatives on [a, b] and coincide on each of the intervals [xj, xj+1] (j=0, 1, ..., m) with some polynomial from the system {ui(t)} i=0 n .THEOREM. For every continuous function on [a, b] there exists in Sn,m a unique element of best mean approximation. 相似文献
12.
Raffaella Cilia Joaquín M. Gutirrez 《Journal of Mathematical Analysis and Applications》2009,360(2):609-623
It is well known that a (linear) operator between Banach spaces is completely continuous if and only if its adjoint takes bounded subsets of Y* into uniformly completely continuous subsets, often called (L)-subsets, of X*. We give similar results for differentiable mappings. More precisely, if UX is an open convex subset, let be a differentiable mapping whose derivative is uniformly continuous on U-bounded subsets. We prove that f takes weak Cauchy U-bounded sequences into convergent sequences if and only if f′ takes Rosenthal U-bounded subsets of U into uniformly completely continuous subsets of . As a consequence, we extend a result of P. Hájek and answer a question raised by R. Deville and E. Matheron. We derive differentiable characterizations of Banach spaces not containing ℓ1 and of Banach spaces without the Schur property containing a copy of ℓ1. Analogous results are given for differentiable mappings taking weakly convergent U-bounded sequences into convergent sequences. Finally, we show that if X has the hereditary Dunford–Pettis property, then every differentiable function as above is locally weakly sequentially continuous. 相似文献
13.
A. Amini-Harandi A.P. Farajzadeh 《Nonlinear Analysis: Theory, Methods & Applications》2009,71(11):5151-5156
Suppose X is a compact admissible subset of a hyperconvex metric spaces M, and suppose F:XM is a quasi-lower semicontinuous set-valued map whose values are nonempty admissible. Suppose also G:XX is a continuous, onto quasi-convex set-valued map with compact, admissible values. Then there exists an x0X such that
14.
Ruey-Jen Jang-Lewis Harold Dean Victory Jr. 《Integral Equations and Operator Theory》1994,18(1):88-108
LetE be a Banach lattice having order continuous norm. Suppose, moreover,T is a nonnegative reducible operator having a compact iterate and which mapsE into itself. The purpose of this work is to extend the previous results of the authors, concerning nonnegative solvability of (kernel) operator equations on generalL
p-spaces. In particular, we provide necessary and sufficient conditions for the operator equation x=T
x+y to possess a nonnegative solutionxE wherey is a given nonnegative and nontrivial element ofE and is any given positive parameter. 相似文献
15.
H. Kerner 《The Journal of the Operational Research Society》1961,12(4):226-243
The paper deals with the batch size problem, given that demand is batch-wise and the times and quantities of the first n demands are known. This is found to be a problem in dynamic programming.A treatment is devised which may often enable that part of the demand to be scheduled optimally which must be procured before further information becomes available; which solves the problem in such cases. In other cases the final decision between the surviving possibilities may have to be based on possibly non-optimal criteria. Where it is known that the nth demand is the last, the problem can be solved completely.Details of computational methods are given, including worked examples. The methods appear suitable for computer programming, but are in any case (relatively) fast by hand; a solution may normally be obtained in, say, 5n minutes or less, except where the individual demands are much smaller than the optimum batch size (in which case other—approximate—methods may be preferred and would be unlikely to incur much penalty). 相似文献
16.
《European Journal of Operational Research》2006,175(3):1455-1471
The continuous dynamic network loading problem (CDNLP) aims to compute link travel times and path travel times on a congested network, given time-dependent path flow rates for a given time period. A crucial element of CDNLP is a model of the link performance. Two main modeling frameworks have been used in link loading models: The so-called whole-link travel time (WTT) models and the kinematic wave model of Lighthill–Whitham–Richards (LWR) for traffic flow.In this paper, we reformulate a well-known whole-link model in which the link travel time, for traffic entering a time t, is a function of the number of vehicles on link. This formulation does not require the satisfying of the FIFO (first in, first out) condition. An extension of the basic WTT model is proposed in order to take explicitly into account the maximum number of vehicles that the link can accommodate (occupancy constraint). A solution scheme for the proposed WTT model is derived.Several numerical examples are given to illustrate that the FIFO condition is not respected for the WTT model and to compare the travel time predictions effected by LWR and WTT models. 相似文献
17.
Valentin Gutev Tsugunori Nogura 《Proceedings of the American Mathematical Society》2001,129(9):2809-2815
Suppose that is a Hausdorff space such that its Vietoris hyperspace has a continuous selection. Do disconnectedness-like properties of depend on the variety of continuous selections for and vice versa? In general, the answer is ``yes' and, in some particular situations, we were also able to set proper characterizations. 18.
Z. I. Borevich 《Journal of Mathematical Sciences》1982,19(1):977-981
Suppose G is a group and D a subgroup. A system, of intermediate subgroups G
and their normalizers is called a fan for D if for each intermediate sub group H (D HG) there exists a unique index such that. If there exists a fan for D, then D is called a fan subgroup of G. Examples of fans and fan subgroups are given. A standard fan is distinguished, for which all of the groups G
are generated by sets of subgroups conjugate to D. The question of the uniqueness of a fan is discussed. It is proved that any pronormal subgroup is a fan subgroup, and some properties of its fan are noted.Translated from Zapiski Nauchnykh Seminarov Leningradskogo Otdeleniya Matematicheskogo Instituta im. V. A. Steklova AN SSSR, Vol. 94, pp. 5–12, 1979. 相似文献
19.
It is proved in this paper that for a continuous B-domain L, the function space [X→L] is continuous for each core compact and coherent space X. Further, applications are given. It is proved that:
20.
Suppose A generates a strongly continuous linear group
on a Banach space X and B is a linear operator on X. It is shown that an extension of
generates a strongly continuous semigroup if and only if the family of operators
has an appropriate evolution system. This produces simple sufficient conditions for an extension of
to generate a strongly continuous semigroup, including
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