International Journal of Combinatorics
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The latest articles from Hindawi Publishing Corporation
© 2016 , Hindawi Publishing Corporation . All rights reserved.

On SelfCenteredness of Product of Graphs
Sun, 07 Aug 2016 07:51:09 +0000
http://www.hindawi.com/journals/ijcom/2016/2508156/
A graph is said to be a selfcentered graph if the eccentricity of every vertex of the graph is the same. In other words, a graph is a selfcentered graph if radius and diameter of the graph are equal. In this paper, selfcenteredness of strong product, conormal product, and lexicographic product of graphs is studied in detail. The necessary and sufficient conditions for these products of graphs to be a selfcentered graph are also discussed. The distance between any two vertices in the conormal product of a finite number of graphs is also computed analytically.
Priyanka Singh and Pratima Panigrahi
Copyright © 2016 Priyanka Singh and Pratima Panigrahi. All rights reserved.

A New Relationship between Block Designs
Thu, 28 Jul 2016 06:22:40 +0000
http://www.hindawi.com/journals/ijcom/2016/7092474/
We propose a procedure of constructing new block designs starting from a given one by looking at the intersections of its blocks with various sets and grouping those sets according to the structure of the intersections. We introduce a symmetric relationship of friendship between block designs built on a set and consider families of block designs where all designs are friends of each other, the socalled friendly families. We show that a friendly family admits a partial ordering. Furthermore, we exhibit a map from the power set of , partially ordered by inclusion, to a friendly family of a particular type which preserves the partial order.
Alexander Shramchenko and Vasilisa Shramchenko
Copyright © 2016 Alexander Shramchenko and Vasilisa Shramchenko. All rights reserved.

Some Nonexistence and Asymptotic Existence Results for Weighing Matrices
Sun, 13 Mar 2016 08:33:50 +0000
http://www.hindawi.com/journals/ijcom/2016/2162849/
Orthogonal designs and weighing matrices have many applications in areas such as coding theory, cryptography, wireless networking, and communication. In this paper, we first show that if positive integer cannot be written as the sum of three integer squares, then there does not exist any skewsymmetric weighing matrix of order and weight , where is an odd positive integer. Then we show that, for any square , there is an integer such that, for each , there is a symmetric weighing matrix of order and weight . Moreover, we improve some of the asymptotic existence results for weighing matrices obtained by Eades, Geramita, and Seberry.
Ebrahim Ghaderpour
Copyright © 2016 Ebrahim Ghaderpour. All rights reserved.

Starter Labelling of Windmill Graphs with Small Defects
Mon, 17 Aug 2015 07:40:13 +0000
http://www.hindawi.com/journals/ijcom/2015/528083/
A graph on vertices can be starterlabelled, if the vertices can be given labels from the nonzero elements of the additive group such that each label , either or , is assigned to exactly two vertices and the two vertices are separated by either edges or edges, respectively. Mendelsohn and Shalaby have introduced Skolemlabelled graphs and determined the conditions of windmills to be Skolemlabelled. In this paper, we introduce starterlabelled graphs and obtain necessary and sufficient conditions for starter and minimum hooked starter labelling of all windmills.
Farej Omer and Nabil Shalaby
Copyright © 2015 Farej Omer and Nabil Shalaby. All rights reserved.

A Formula for the Reliability of a Dimensional Consecutiveoutof:F System
Mon, 13 Jul 2015 10:58:05 +0000
http://www.hindawi.com/journals/ijcom/2015/140909/
We derive a formula for the reliability of a dimensional consecutiveoutof:F system, that is, a formula for the probability that an array whose entries are (independently of each other) 0 with probability and 1 with probability does not include a contiguous subarray whose every entry is 1.
Simon Cowell
Copyright © 2015 Simon Cowell. All rights reserved.

On 3Regular Bipancyclic Subgraphs of Hypercubes
Tue, 05 May 2015 09:36:04 +0000
http://www.hindawi.com/journals/ijcom/2015/638767/
The dimensional hypercube is bipancyclic; that is, it contains a cycle of every even length from 4 to . In this paper, we prove that contains a 3regular, 3connected, bipancyclic subgraph with vertices for every even from 8 to except 10.
Y. M. Borse and S. R. Shaikh
Copyright © 2015 Y. M. Borse and S. R. Shaikh. All rights reserved.

On EvenlyEquitable, Balanced EdgeColorings and Related Notions
Wed, 04 Mar 2015 06:53:37 +0000
http://www.hindawi.com/journals/ijcom/2015/201427/
A graph is said to be even if all vertices of have even degree. Given a edgecoloring of a graph , for each color let denote the spanning subgraph of in which the edgeset contains precisely the edges colored . A edgecoloring of is said to be an edgecoloring if for each color , is an even graph. A edgecoloring of is said to be evenlyequitable if for each color , is an even graph, and for each vertex and for any pair of colors , . For any pair of vertices let be the number of edges between and in (we allow , where denotes a loop incident with ). A edgecoloring of is said to be balanced if for all pairs of colors and and all pairs of vertices and (possibly ), . Hilton proved that each even graph has an evenlyequitable edgecoloring for each . In this paper we extend this result by finding a characterization for graphs that have an evenlyequitable, balanced edgecoloring for each . Correspondingly we find a characterization for even graphs to have an evenlyequitable, balanced 2edgecoloring. Then we give an instance of how evenlyequitable, balanced edgecolorings can be used to determine if a certain fairness property of factorizations of some regular graphs is satisfied. Finally we indicate how different fairness notions on edgecolorings interact with each other.
Aras Erzurumluoğlu and C. A. Rodger
Copyright © 2015 Aras Erzurumluoğlu and C. A. Rodger. All rights reserved.

The Class of Cliqued Graphs: EigenBiBalanced Characteristic, Designs, and an Entomological Experiment
Mon, 02 Mar 2015 09:52:57 +0000
http://www.hindawi.com/journals/ijcom/2015/152918/
Much research has involved the consideration of graphs which have subgraphs of a particular kind, such as cliques. Known classes of graphs which are eigenbibalanced, that is, they have a pair a, b of nonzero distinct eigenvalues, whose sum and product are integral, have been investigated. In this paper we will define a new class of graphs, called qcliqued graphs, on vertices, which contain cliques each of order connected to a central vertex, and then prove that these cliqued graphs are eigenbibalanced with respect to a conjugate pair whose sum is and product . These graphs can be regarded as design graphs, and we use a specific example in an entomological experiment.
Paul August Winter, Carol Lynne Jessop, and Costas Zachariades
Copyright © 2015 Paul August Winter et al. All rights reserved.

Hamilton Paths and Cycles in Varietal Hypercube Networks with Mixed Faults
Thu, 22 Jan 2015 13:47:02 +0000
http://www.hindawi.com/journals/ijcom/2015/513073/
This paper considers the varietal hypercube network with mixed faults and shows that contains a faultfree Hamilton cycle provided faults do not exceed for and contains a faultfree Hamilton path between any pair of vertices provided faults do not exceed for . The proof is based on an inductive construction.
JianGuang Zhou and JunMing Xu
Copyright © 2015 JianGuang Zhou and JunMing Xu. All rights reserved.

Maximal MidpointFree Subsets of Integers
Tue, 20 Jan 2015 12:58:00 +0000
http://www.hindawi.com/journals/ijcom/2015/216475/
A set is midpointfree if no ordered triple satisfies and . Midpointfree subsets of and are studied, with emphasis on those sets characterized by restrictions on the base digits of their elements when , and with particular attention to maximal midpointfree subsets with .
Roger B. Eggleton
Copyright © 2015 Roger B. Eggleton. All rights reserved.

Betweenness Centrality in Some Classes of Graphs
Thu, 25 Dec 2014 13:26:55 +0000
http://www.hindawi.com/journals/ijcom/2014/241723/
There are several centrality measures that have been introduced and studied for realworld networks. They account for the different vertex characteristics that permit them to be ranked in order of importance in the network. Betweenness centrality is a measure of the influence of a vertex over the flow of information between every pair of vertices under the assumption that information primarily flows over the shortest paths between them. In this paper we present betweenness centrality of some important classes of graphs.
Sunil Kumar Raghavan Unnithan, Balakrishnan Kannan, and Madambi Jathavedan
Copyright © 2014 Sunil Kumar Raghavan Unnithan et al. All rights reserved.

On Some Bounds and Exact Formulae for Connective Eccentric Indices of Graphs under Some Graph Operations
Wed, 24 Dec 2014 11:22:31 +0000
http://www.hindawi.com/journals/ijcom/2014/579257/
The connective eccentric index of a graph is a topological index involving degrees and eccentricities of vertices of the graph. In this paper, we have studied the connective eccentric index for double graph and double cover. Also we give the connective eccentric index for some graph operations such as joins, symmetric difference, disjunction, and splice of graphs.
Nilanjan De, Anita Pal, and Sk. Md. Abu Nayeem
Copyright © 2014 Nilanjan De et al. All rights reserved.

Extremal Unimodular Lattices in Dimension 36
Sun, 30 Nov 2014 16:47:35 +0000
http://www.hindawi.com/journals/ijcom/2014/792471/
New extremal odd unimodular lattices in dimension 36 are constructed. Some new odd unimodular lattices in dimension 36 with long shadows are also constructed.
Masaaki Harada
Copyright © 2014 Masaaki Harada. All rights reserved.

On the General ErdősTurán Conjecture
Mon, 17 Nov 2014 09:34:43 +0000
http://www.hindawi.com/journals/ijcom/2014/826141/
The general ErdősTurán conjecture states that if is an infinite, strictly increasing sequence of natural numbers whose general term satisfies , for some constant and for all , then the number of representations functions of is unbounded. Here, we introduce the function , giving the minimum of the maximal number of representations of a finite sequence of natural numbers satisfying for all . We show that is an increasing function of and that the general ErdősTurán conjecture is equivalent to . We also compute some values of . We further introduce and study the notion of capacity, which is related to the function by the fact that is the capacity of the set of squares of positive integers, but which is also of intrinsic interest.
Georges Grekos, Labib Haddad, Charles Helou, and Jukka Pihko
Copyright © 2014 Georges Grekos et al. All rights reserved.

Characterizing Finite Groups Using the Sum of the Orders of the Elements
Thu, 13 Nov 2014 09:32:41 +0000
http://www.hindawi.com/journals/ijcom/2014/835125/
We give characterizations of various infinite sets of finite groups under the assumption that and the subgroups of satisfy certain properties involving the sum of the orders of the elements of and . Additionally, we investigate the possible values for the sum of the orders of the elements of .
Joshua Harrington, Lenny Jones, and Alicia Lamarche
Copyright © 2014 Joshua Harrington et al. All rights reserved.

Domination Polynomials of kTree Related Graphs
Tue, 11 Nov 2014 07:14:50 +0000
http://www.hindawi.com/journals/ijcom/2014/390170/
Let G be a simple graph of order n. The domination polynomial of G is the polynomial , where d(G, i) is the number of dominating sets of G of size i and γ(G) is the domination number of G. In this paper, we study the domination polynomials of several classes of ktree related graphs. Also, we present families of these kinds of graphs, whose domination polynomials have no nonzero real roots.
Somayeh Jahari and Saeid Alikhani
Copyright © 2014 Somayeh Jahari and Saeid Alikhani. All rights reserved.

Necklaces, SelfReciprocal Polynomials, and Cycles
Sun, 09 Nov 2014 07:04:34 +0000
http://www.hindawi.com/journals/ijcom/2014/593749/
Let be a positive integer and a prime power. Consider necklaces consisting of beads, each of which has one of the given colors. A primitive orbit is an equivalence class of necklaces closed under rotation. A orbit is selfcomplementary when it is closed under an assigned color matching. In the work of Miller (1978), it is shown that there is a 11 correspondence between the set of primitive, selfcomplementary orbits and that of selfreciprocal irreducible monic (srim) polynomials of degree . Let be a positive integer relatively prime to . A cycle mod is a finite sequence of nonnegative integers closed under multiplication by . In the work of Wan (2003), it is shown that cycles mod are closely related to monic irreducible divisors of . Here, we show that: (1) cycles can be used to obtain information about srim polynomials; (2) there are correspondences among certain cycles and orbits; (3) there are alternative proofs of Miller's results in the work of Miller (1978) based on the use of cycles.
Umarin Pintoptang, Vichian Laohakosol, and Suton Tadee
Copyright © 2014 Umarin Pintoptang et al. All rights reserved.

Some Properties of the Intersection Graph for Finite Commutative Principal Ideal Rings
Thu, 25 Sep 2014 07:44:53 +0000
http://www.hindawi.com/journals/ijcom/2014/952371/
Let R be a commutative finite principal ideal ring with unity, and let G(R) be the simple graph consisting of nontrivial proper ideals of R as vertices such that two vertices I and J are adjacent if they have nonzero intersection. In this paper we continue the work done by Abu Osba. We calculate the radius, eccentricity, domination number, independence number, geodetic number, and the hull number for this graph. We also determine when G(R) is chordal. Finally, we study some properties of the complement graph of G(R).
Emad Abu Osba, Salah AlAddasi, and Omar Abughneim
Copyright © 2014 Emad Abu Osba et al. All rights reserved.

Integral EigenPair Balanced Classes of Graphs with Their Ratio, Asymptote, Area, and InvolutionComplementary Aspects
Tue, 23 Sep 2014 09:08:46 +0000
http://www.hindawi.com/journals/ijcom/2014/148690/
The association of integers, conjugate pairs, and robustness with the eigenvalues of graphs provides the motivation for the following definitions. A class of graphs, with the property that, for each graph (member) of the class, there exists a pair of nonzero, distinct eigenvalues, whose sum and product are integral, is said to be eigenbibalanced. If the ratio is a function , of the order of the graphs in this class, then we investigate its asymptotic properties. Attaching the average degree to the Riemann integral of this ratio allowed for the evaluation of eigenbalanced areas of classes of graphs. Complete graphs on vertices are eigenbibalanced with the eigenbalanced ratio which is asymptotic to the constant value of −1. Its eigenbalanced area is —we show that this is the maximum area for most known classes of eigenbibalanced graphs. We also investigate the class of eigenbibalanced graphs, whose class of complements gives rise to an eigenbalanced asymptote that is an involution and the effect of the asymptotic ratio on the energy of the graph theoretical representation of molecules.
Paul August Winter and Carol Lynne Jessop
Copyright © 2014 Paul August Winter and Carol Lynne Jessop. All rights reserved.

Modular Leech Trees of Order at Most 8
Thu, 18 Sep 2014 10:54:22 +0000
http://www.hindawi.com/journals/ijcom/2014/218086/
In 1975, John Leech asked when can the edges of a tree on vertices be labeled with positive integers such that the sums along the paths are exactly the integers . He found five such trees, and no additional trees have been discovered since. In 2011 Leach and Walsh introduced the idea of labeling trees with elements of the group where and examined the cases for . In this paper we show that no modular Leech trees of order 7 exist, and we find all modular Leech trees of order 8.
David Leach
Copyright © 2014 David Leach. All rights reserved.

MidpointFree Subsets of the Real Numbers
Tue, 26 Aug 2014 08:07:57 +0000
http://www.hindawi.com/journals/ijcom/2014/214637/
A set of reals is midpointfree if it has no subset such that and . If and is midpointfree, it is a maximal midpointfree subset of if there is no midpointfree set such that . In each of the cases , we determine two maximal midpointfree subsets of characterised by digit constraints on the base 3 representations of their members.
Roger B. Eggleton
Copyright © 2014 Roger B. Eggleton. All rights reserved.

Normal EdgeTransitive Cayley Graphs of the Group
Tue, 19 Aug 2014 00:00:00 +0000
http://www.hindawi.com/journals/ijcom/2014/628214/
A Cayley graph of a group is called normal edgetransitive if the normalizer of the right representation of the group in the automorphism of the Cayley graph acts transitively on the set of edges of the graph. In this paper, we determine all connected normal edgetransitive Cayley graphs of the group .
A. Assari and F. Sheikhmiri
Copyright © 2014 A. Assari and F. Sheikhmiri. All rights reserved.

On the Genus of the ZeroDivisor Graph of
Tue, 22 Jul 2014 08:04:37 +0000
http://www.hindawi.com/journals/ijcom/2014/390732/
Let be a commutative ring with identity. The zerodivisor graph of , denoted , is the simple graph whose vertices are the nonzero zerodivisors of , and two distinct vertices and are linked by an edge if and only if . The genus of a simple graph is the smallest integer such that can be embedded into an orientable surface . In this paper, we determine that the genus of the zerodivisor graph of , the ring of integers modulo , is two or three.
Huadong Su and Pailing Li
Copyright © 2014 Huadong Su and Pailing Li. All rights reserved.

A Weighted Regularity Lemma with Applications
Thu, 19 Jun 2014 11:48:40 +0000
http://www.hindawi.com/journals/ijcom/2014/602657/
We prove an extension of the regularity lemma with vertex and edge weights which in principle can be applied for arbitrary graphs. The applications involve random graphs and a weighted version of the ErdősStone theorem. We also provide means to handle the otherwise uncontrolled exceptional set.
Béla Csaba and András Pluhár
Copyright © 2014 Béla Csaba and András Pluhár. All rights reserved.

Decomposition Formulas for Triple Hypergeometric Functions
Thu, 15 May 2014 12:45:07 +0000
http://www.hindawi.com/journals/ijcom/2014/712321/
In the spirit of Hasanov, Srivastava, and Turaev (2006), we introduce new inverse operators together with a more general operator and find a summation formula for the last one. Based on these operators and the earlier known analogues of the BurchnallChaundy operators, we find 15 symbolic operator formulas. Then, 10 expansions for the analogues of Srivastava’s three triple hypergeometric functions in terms of hypergeometric and Kampé de Fériet functions are derived. These expansions readily reduce to 10 new expansions for the three triple Srivastava hypergeometric functions in terms of hypergeometric and Kampé de Fériet functions.
Thomas Ernst
Copyright © 2014 Thomas Ernst. All rights reserved.

The Terminal Hosoya Polynomial of Some Families of Composite Graphs
Wed, 16 Apr 2014 08:34:46 +0000
http://www.hindawi.com/journals/ijcom/2014/696507/
Let be a connected graph and let be the set of pendent vertices of . The terminal Hosoya polynomial of is defined as , where denotes the distance between the pendent vertices and . In this note paper we obtain closed formulae for the terminal Hosoya polynomial of rooted product graphs and corona product graphs.
Emeric Deutsch and Juan Alberto RodríguezVelázquez
Copyright © 2014 Emeric Deutsch and Juan Alberto RodríguezVelázquez. All rights reserved.

Bounds on the Size of the Minimum Dominating Sets of Some Cylindrical Grid Graphs
Mon, 07 Apr 2014 13:46:57 +0000
http://www.hindawi.com/journals/ijcom/2014/348359/
Let denote the domination number of the cylindrical grid graph formed by the Cartesian product of the graphs , the path of length m, and the graph , the cycle of length n, . In this paper we propose methods to find the domination numbers of graphs of the form with and and propose tight bounds on domination numbers of the graphs , . Moreover, we provide rough bounds on domination numbers of the graphs , and . We also point out how domination numbers and minimum dominating sets are useful for wireless sensor networks.
Mrinal Nandi, Subrata Parui, and Avishek Adhikari
Copyright © 2014 Mrinal Nandi et al. All rights reserved.

On the Cardinality of the Topologies on a Finite Set
Mon, 31 Mar 2014 07:10:42 +0000
http://www.hindawi.com/journals/ijcom/2014/798074/
Let be the number of all labeled topologies having open sets that we can define on points, and let be the number of those which are nonhomeomorphic. In this paper, we compute these numbers for and arbitrary . The numbers of all unlabeled and nontopologies with open sets are also given for .
Messaoud Kolli
Copyright © 2014 Messaoud Kolli. All rights reserved.

Embedding Structures Associated with Riordan Arrays and Moment Matrices
Mon, 17 Mar 2014 07:02:22 +0000
http://www.hindawi.com/journals/ijcom/2014/301394/
Every ordinary Riordan array contains two naturally embedded Riordan arrays. We explore this phenomenon, and we compare it to the situation for certain moment matrices of families of orthogonal polynomials.
Paul Barry
Copyright © 2014 Paul Barry. All rights reserved.

The Path Cover Polynomial of a Graph and a Model for General Coefficient Linear Recurrences
Sun, 12 Jan 2014 00:00:00 +0000
http://www.hindawi.com/journals/ijcom/2014/258017/
An path cover of a simple graph is a set of vertex disjoint paths of , each with vertices, that span . With every we associate a weight, , and define the weight of to be . The path cover polynomial of is then defined as where the sum is taken over all path covers of . This polynomial is a specialization of the pathcover polynomial of Farrell. We consider the path cover polynomial of a weighted path and find the term recurrence that it satisfies. The matrix form of this recurrence yields a formula equating the trace of the recurrence matrix with the path cover polynomial of a suitably weighted cycle . A directed graph, , the edgeweighted trellis, is introduced and so a third way to generate the solutions to the above term recurrence is presented. We also give a model for generalterm linear recurrences and timedependent Markov chains.
John P. McSorley and Philip Feinsilver
Copyright © 2014 John P. McSorley and Philip Feinsilver. All rights reserved.