共查询到20条相似文献,搜索用时 31 毫秒
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Nechemia Burshtein 《Discrete Mathematics》2005,300(1-3):213-217
Questions, partial and complete answers about the diophantine equation in distinct positive integers are given when additional requirements are asked on the xi's such as: being large, odd, even or xixj for i≠j. Various combinations of the above conditions are also considered. 相似文献
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Ralph J. Faudree Ronald J. Gould Michael S. Jacobson Linda Lesniak Akira Saito 《Discrete Mathematics》2005,300(1-3):218-224
In this note, we consider a minimum degree condition for a hamiltonian graph to have a 2-factor with two components. Let G be a graph of order n3. Dirac's theorem says that if the minimum degree of G is at least , then G has a hamiltonian cycle. Furthermore, Brandt et al. [J. Graph Theory 24 (1997) 165–173] proved that if n8, then G has a 2-factor with two components. Both theorems are sharp and there are infinitely many graphs G of odd order and minimum degree which have no 2-factor. However, if hamiltonicity is assumed, we can relax the minimum degree condition for the existence of a 2-factor with two components. We prove in this note that a hamiltonian graph of order n6 and minimum degree at least has a 2-factor with two components. 相似文献
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In order to avoid interference in cellular telephone networks, sets of radio frequencies are to be assigned to transmitters such that adjacent transmitters are allotted disjoint sets of frequencies. Often these transmitters are laid out like vertices of a triangular lattice in a plane. This problem corresponds to the problem of multicoloring an induced subgraph of a triangular lattice with integer demands associated with each vertex. We deal with the simpler case of triangle-free subgraphs of the lattice. [Frédéric Havet, Discrete Math. 233 (2001) 1–3] uses inductive arguments to prove that triangle-free hexagonal graphs can be colored with colors where ωd is the maximum demand on a clique in the graph. We give a simpler proof and hope that our techniques can be used to prove the conjecture by [McDiarmid and Reed, Networks Suppl. 36 (2000) 114–117] that these graphs are -multicolorable. 相似文献
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David J. Grynkiewicz 《Discrete Mathematics》2005,290(2-3):165-171
Let m and r be positive integers. Define f(m,r) to be the least positive integer N such that for every coloring of the integers 1,…,N with r colors there exist monochromatic subsets B1 and B2 (not necessarily of the same color), each having m elements, such that (a) max(B1)-min(B1)max(B2)-min(B2), and (b) max(B1)B2) . We improve previous upper bounds to determine that f(m,4)=12m-9. 相似文献
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The duality and primitivity of the association scheme Qua(n,q) of quadratic forms in n variables and the association scheme Sym(n,q) of symmetric bilinear forms in n variables over the finite field are discussed by Wang et al. [Association schemes of quadratic forms and symmetric bilinear forms, J. Algebraic Combin. 17 (2003) 149–161]. In this paper, eigenvalues of Qua(n,q) are computed, where q is a power of 2. As an application, two fusion schemes of Qua(n,q) are discussed and their dual schemes are constructed. 相似文献
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Two uniform asymptotic expansions are obtained for the Pollaczek polynomials Pn(cosθ;a,b). One is for , , in terms of elementary functions and in descending powers of . The other is for , in terms of a special function closely related to the modified parabolic cylinder functions, in descending powers of n. This interval contains a turning point and all possible zeros of Pn(cosθ) in θ(0,π/2]. 相似文献
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A weighted graph is one in which every edge e is assigned a nonnegative number w(e), called the weight of e. For a vertex v of a weighted graph, dw(v) is the sum of the weights of the edges incident to v. And the weight of a path is the sum of the weights of the edges belonging to it. In this paper, we give a sufficient condition for a weighted graph to have a heavy path which joins two specified vertices. Let G be a 2-connected weighted graph and let x and y be distinct vertices of G. Suppose that dw(u)+dw(v)2d for every pair of non-adjacent vertices u and vV(G) x,y . Then x and y are joined by a path of weight at least d, or they are joined by a Hamilton path. Also, we consider the case when G has some vertices whose weighted degree are not assumed. 相似文献
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In this paper, we shall prove that there is no [3q4-q3-q2-3q-1,5,3q4-4q3-2q+1]q code over the finite field for q11. Thus, we conclude the nonexistence of a [gq(5,d),5,d]q code for 3q4-4q3-2q+1d3q4-4q3-q. 相似文献
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Let G be a doubly but not triply transitive group on a set X. We give an algorithm to construct the orbits of G acting on X×X×X by combining those of its stabilizer H of a point of X If the group H is given first, we compute the orbits of its transitive extension G, if it exists. We apply our algorithm to G=PSL(m,q) and Sp(2m,2), m3, successfully. We go forward to compute the transitive extension of G itself. In our construction we use a superscheme defined by the orbits of H on X×X×X and do not use group elements. 相似文献
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Let T be a partial latin square and L be a latin square with TL. We say that T is a latin trade if there exists a partial latin square T′ with T′∩T= such that (LT)T′ is a latin square. A k-homogeneous latin trade is one which intersects each row, each column and each entry either 0 or k times. In this paper, we construct 3-homogeneous latin trades from hexagonal packings of the plane with circles. We show that 3-homogeneous latin trades of size 3 m exist for each m3. This paper discusses existence results for latin trades and provides a glueing construction which is subsequently used to construct all latin trades of finite order greater than three. 相似文献
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Given a graph G, a proper labeling f of G is a one-to-one function . The bandwidth sum of a graph G, denoted by Bs(G), is defined by Bs(G)=min∑uvE(G)|f(u)-f(v)|, where the minimum is taken for all proper labelings f of G. In this paper, we give some results for the bandwidth sum problem for the join of k graphs G1,G2,…,Gk, where each Gi is a path, cycle, complete graph, or union of isolated vertices. We also discuss the bandwidth sum for the composition of two graphs G and H, where G and H are path, cycle, or union of isolated vertices. 相似文献
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A. Ballester-Bolinches L.A. Kurdachenko Tatiana Pedraza 《Journal of Pure and Applied Algebra》2007,210(3):665-671
A group G is said to be a -group if permutability is a transitive relation in the set of all subgroups of G. Our purpose in this paper is to study -groups in the class of periodic radical groups satisfying min-p for all primes p. 相似文献
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In the present note, we investigate schemes S in which each element s satisfies ns2 and ns*s≠2. We show that such a scheme is schurian. More precisely, we show that it is isomorphic to G//t, where G is a finite group and t an involution of G weakly closed in CG(t).
Groups G with an involution t weakly closed in CG(t) have been described in Glauberman's Z*-Theorem [G. Glauberman, Central elements in core-free groups, J. Algebra 4 (1966) 403–420] with the help of the largest normal subgroup of G having odd order. 相似文献
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The performance of a linear t-error correcting code over a q-ary symmetric memoryless channel with symbol error probability ε is characterized by the probability that a transmission error will remain undetected. This probability is a function of ε involving the code weight distribution and the weight distribution of the cosets of minimum weight at most t. When the undetectable error probability is an increasing function of ε, the code is called t-proper.
The paper presents sufficient conditions for t-properness and a list of codes known to be proper, many of which have been studied by these sufficient conditions. Special attention is paid to error detecting codes of interest in modern communication. 相似文献
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We prove that when q is any odd prime power, the distance-2 graph on the set of vertices at maximal distance D from any fixed vertex of the Hemmeter graph HemD(q) is isomorphic to the graph QuadD-1(q) of quadratic forms on . 相似文献
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Takeshi Torii 《Topology and its Applications》2005,150(1-3):33-57
We have a ring homomorphism Θ from the cohomology of the extended Morava stabilizer group Gn with coefficients in F[w±1] to the cohomology of Gn+1 with coefficients in the graded field F((un))[u±1]. In this note we study the behavior of Θ on H1. Then it is shown that Θ is injective on H1 for n1 and for all primes p. 相似文献
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In this paper we study the number of spanning forests of a graph. Let G be a connected simple graph. (1) We give a lower bound for the number of spanning forests of G in terms of the edge connectivity of G. (2) We give an upper bound for the number of rooted spanning forests of G. (3) We describe the elementary symmetric functions of inverse positive Laplacian eigenvalues of a tree. (4) We determine all Laplacian integral graphs with prime number of spanning trees. (5) We give a simple proof of a theorem of K. Hashimoto on Ihara zeta function. 相似文献