共查询到20条相似文献,搜索用时 29 毫秒
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S. Jahanbekam 《Discrete Applied Mathematics》2009,157(2):400-401
Let G be a graph of order n and denote the signed edge domination number of G. In [B. Xu, Two classes of edge domination in graphs, Discrete Appl. Math. 154 (2006) 1541-1546] it was proved that for any graph G of order n, . But the method given in the proof is not correct. In this paper we give an example for which the method of proof given in [1] does not work. 相似文献
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On edge domination numbers of graphs 总被引:1,自引:0,他引:1
Baogen Xu 《Discrete Mathematics》2005,294(3):311-316
Let and be the signed edge domination number and signed star domination number of G, respectively. We prove that holds for all graphs G without isolated vertices, where n=|V(G)|?4 and m=|E(G)|, and pose some problems and conjectures. 相似文献
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A discrete function f defined on Zn is said to be logconcave if for , , . A more restrictive notion is strong unimodality. Following Barndorff-Nielsen [O. Barndorff-Nielsen, Unimodality and exponential families, Commun. Statist. 1 (1973) 189-216] a discrete function is called strongly unimodal if there exists a convex function such that if . In this paper sufficient conditions that ensure the strong unimodality of a multivariate discrete distribution, are given. Examples of strongly unimodal multivariate discrete distributions are presented. 相似文献
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Adrian Kosowski 《Discrete Applied Mathematics》2009,157(2):321-329
Motivated by wavelength-assignment problems for all-to-all traffic in optical networks, we study graph parameters related to sets of paths connecting all pairs of vertices. We consider sets of both undirected and directed paths, under minimisation criteria known as edge congestion and wavelength count; this gives rise to four parameters of a graph G: its edge forwarding index π(G), arc forwarding index , undirected optical index , and directed optical index .In the paper we address two long-standing open problems: whether the equality holds for all graphs, and whether indices π(G) and are hard to compute. For the first problem, we give an example of a family of planar graphs {Gk} such that . For the second problem, we show that determining either π(G) or is NP-hard. 相似文献
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Jin-Hui Fang 《Discrete Applied Mathematics》2008,156(15):2950-2958
It is conjectured by Erd?s, Graham and Spencer that if 1≤a1≤a2≤?≤as are integers with , then this sum can be decomposed into n parts so that all partial sums are ≤1. This is not true for as shown by a1=?=an−2=1, . In 1997 Sandor proved that Erd?s-Graham-Spencer conjecture is true for . Recently, Chen proved that the conjecture is true for . In this paper, we prove that Erd?s-Graham-Spencer conjecture is true for . 相似文献
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We improve parts of the results of [T. W. Cusick, P. Stanica, Fast evaluation, weights and nonlinearity of rotation-symmetric functions, Discrete Mathematics 258 (2002) 289-301; J. Pieprzyk, C. X. Qu, Fast hashing and rotation-symmetric functions, Journal of Universal Computer Science 5 (1) (1999) 20-31]. It is observed that the n-variable quadratic Boolean functions, for , which are homogeneous rotation symmetric, may not be affinely equivalent for fixed n and different choices of s. We show that their weights and nonlinearity are exactly characterized by the cyclic subgroup 〈s−1〉 of Zn. If , the order of s−1, is even, the weight and nonlinearity are the same and given by . If the order is odd, it is balanced and nonlinearity is given by . 相似文献
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Mitsuru Uchiyama 《Journal of Functional Analysis》2006,231(1):221-244
Let P+ be the set of all non-negative operator monotone functions defined on [0,∞), and put . Then and . For a function and a strictly increasing function h we write if is operator monotone. If and and if and , then . We will apply this result to polynomials and operator inequalities. Let and be non-increasing sequences, and put for t≧a1 and for t≧b1. Then v+?u+ if m≦n and : in particular, for a sequence of orthonormal polynomials, (pn-1)+?(pn)+. Suppose 0<r,p and s=0 or 1≦s≦1+p/r. Then 0≦A≦B implies for 0<α≦r/(p+r). 相似文献
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Sachin Gautam Ashish Kumar Srivastava Amitabha Tripathi 《Discrete Applied Mathematics》2008,156(12):2423-2428
Given graphs , where k≥2, the notation
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We give a characterization of exponentiable monomorphisms in the categories of ω-complete posets, of directed complete posets and of continuous directed complete posets as those monotone maps f that are convex and that lift an element (and then a queue) of any directed set (ω-chain in the case of ) whose supremum is in the image of f (Theorem 1.9). Using this characterization, we obtain that a monomorphism f:X→B in (, ) exponentiable in w.r.t. the Scott topology is exponentiable also in (, ). We prove that the converse is true in the category , but neither in , nor in . 相似文献
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Anvesh Komuravelli 《Discrete Applied Mathematics》2009,157(16):3372-3385
An N-dimensional digital binary image (I) is a function I:ZN→{0,1}. I is connected if and only if its black pixels and white pixels are each (3N−1)-connected. I is only connected if and only if its black pixels are (3N−1)-connected. For a 3-D binary image, the respective connectivity models are and . A pair of (3N−1)-neighboring opposite-valued pixels is called interchangeable in a N-D binary image I, if reversing their values preserves the original connectedness. We call such an interchange to be a (3N−1)-local interchange. Under the above connectivity models, we show that given two binary images of n pixels/voxels each, we can transform one to the other using a sequence of (3N−1)-local interchanges. The specific results are as follows. Any two -connected 3-dimensional images I and J each having n black voxels are transformable using a sequence of O((c1+c2)n2) 26-local interchanges. Here, c1 and c2 are the total number of 8-connected components in all 2-dimensional layers of I and J respectively. We also show bounds on connectivity under a different interchange model as proposed in [A. Dumitrescu, J. Pach, Pushing squares around, Graphs and Combinatorics 22 (1) (2006) 37-50]. Next, we show that any two simply connected images under the , connectivity model and each having n black voxels are transformable using a sequence of O(n2) 26-local interchanges. We generalize this result to show that any two , -connected N-dimensional simply connected images each having n black pixels are transformable using a sequence of O(Nn2)(3N−1)-local interchanges, where N>1. 相似文献
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Improved bounds for acyclic chromatic index of planar graphs 总被引:1,自引:0,他引:1
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Emin Özça? ?nci Ege Ha?met Gürçay 《Journal of Mathematical Analysis and Applications》2007,326(1):101-107
The distributions and were defined as the neutrix limit of the sequences and respectively for , see [J.D. Nicholos, B. Fisher, The distribution composition , J. Math. Anal. Appl. 258 (2001) 131-145; B. Fisher, On defining the distribution , Univ. u Novom Sadu Zb. Rad. Prirod. Mat. Fak. Ser. Mat. 15 (1985) 119-129]. We here consider these distributions when r=0. In other words, we define the sth powers of the Heaviside function H(x) in the distributional sense for negative integers. Further compositions are also considered. 相似文献
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