Let q be a prime power, Fq be the field of q elements, and k, m be positive integers. A bipartite graph G = Gq(g, h, k,m) is defined as follows. The vertex set of G is a union of two copies P and L of two-dimensional vector spaces over Fq, with two vertices (p1, p2) ∈ P and [ l1, l2 ] ∈ L being adjacent if and only if p2 + l2 = p1l 1 . We prove that graphs Gq(k, m) and Gq′(k,m) are isomorphic i...

Let X be an n-set and L a set of nonnegative integers. F , a set of subsets of X, is said to be an L -intersection family if and only if for all E 6= F ∈ F , |E ∩F | ∈ L. A special case of a conjecture of Frankl and Füredi [4] states that if L = {1, 2, . . . , k}, k a positive integer, then |F| ≤ ∑ki=0 (n−1 i ). Here |F| denotes the number of elements in F . Recently Ramanan proved this conject...

The purpose of this paper is to obtain a necessary and sufficient condition for the tensor product of two or more graphs to be connected, bipartite or eulerian. Also, we present a characterization of the duplicate graph $G 1 K_2$ to be unicyclic. Finally, the girth and the formula for computing the number of triangles in the tensor product of graphs are worked out.

In this note we put forward a conjecture on the average optimal length for bipartite matching with a finite number of elements where the different lengths are independent one from the others and have an exponential distribution. The problem of random bipartite matching (or assignment) is interesting both from the point of view of optimisation theory and of statistical mechanics [1, 2, 3, 4]. Ea...

A graph is Bk-VPG when it has an intersection representation by paths in a rectangular grid with at most k bends (turns). It is known that all planar graphs are B3-VPG and this was conjectured to be tight. We disprove this conjecture by showing that all planar graphs are B2-VPG. We also show that the 4-connected planar graphs constitute a subclass of the intersection graphs of Z-shapes (i.e., a...

Connected bipartite permutation graphs without vertex labels are investigated. First, the number of connected bipartite permutation graphs of n vertices is given. Based on the number, a simple algorithm that generates a connected bipartite permutation graph uniformly at random up to isomorphism is presented. Finally an enumeration algorithm of connected bipartite permutation graphs is proposed....

obtain a new for the of a-(u, A) design the block intersection designs are eliminated by an ad hoc coding theoretic argument. A 2-(v, k, A) design 93 is said to be quasi-symmetric if there are two block intersection sizes s1 and s2. The parameters of the complementary design !3* are related to the parameters of 93 as follows: Here Ai denotes the number of blocks through a given i points (and A ...

In this paper, we deal with both the complexity and the approximability of the labeled perfect matching problem in bipartite graphs. Given a simple graph G = (V, E) with n vertices with a color (or label) function L : E → {c1, . . . , cq}, the labeled maximum matching problem consists in finding a maximum matching on G that uses a minimum or a maximum number of colors.

The celebrated Erdös, Faber and Lovász Conjecture may be stated as follows: Any linear hypergraph on v points has chromatic index at most v. We will introduce the linear intersection number of a graph, and use this number to give an alternative formulation of the Erdös, Faber, Lovász conjecture. Finally, first results about the linear intersection number will be proved. For example, the definit...

There is a concept in linear algebra called tridiagonal pair. The was motivated by the theory of $Q$-polynomial distance-regular graphs. We give tutorial introduction to pairs, working with special case as concrete example. totally bipartite, or bipartite (TB). Starting from first principles, we an elementary but comprehensive account TB pairs. following topics are discussed: (i) notion system;...