Tian and Meng in [Y. Tian and J. Meng, c  -Optimally half vertex transitive graphs with regularity , Information Processing Letters 109 (2009) 683-686] shown that a connected half vertex transitive graph with regularity and girth is cyclically optimal. In this paper, we show that a connected half vertex transitive graph G is super cyclically edge-connected if minimum degree k k   6 g G   ...

We study the asymptotic value of several extremal problems on graphs and hypergraphs, that arise as generalized notions of girth. Apart from being combinatorially natural questions, they are motivated by computational-theoretic applications. 1. An `-subgraph is a subgraph with ` edges per vertex, or equivalently, average degree 2`. What is the optimal upper bound S`(n, d), such that any graph o...

The aim of this paper is to give a coherent account of the problem of constructing cubic graphs with large girth. There is a well-defined integer μ0(g), the smallest number of vertices for which a cubic graph with girth at least g exists, and furthermore, the minimum value μ0(g) is attained by a graph whose girth is exactly g. The values of μ0(g) when 3 ≤ g ≤ 8 have been known for over thirty y...

Wang and Lih conjectured that for every g ≥ 5, there exists a number M(g) such that the chromatic number of the square of every planar graph of girth at least g and maximum degree ∆ ≥ M(g) is ∆ + 1. We disprove the conjecture for g ∈ {5, 6} and prove the existence of the number M(g) for g ≥ 7. More generally, we show that every planar graph of girth at least 7 and maximum degree ∆ ≥ 190 + 2dp/q...

It was proved in [Z. Dvořàk, D. Kràl, P. Nejedlỳ, R. Škrekovski, Coloring squares of planar graphs with girth six, European J. Combin. 29 (4) (2008) 838–849] that every planar graph with girth g ≥ 6 and maximum degree ∆ ≥ 8821 is 2-distance (∆ + 2)-colorable. We prove that every planar graph with g ≥ 6 and∆ ≥ 18 is 2-distance (∆+ 2)-colorable. © 2009 Elsevier B.V. All rights reserved.

Lower bounds on the subdominant eigenvalue of regular graphs of given girth are derived. Our approach is to approximate the discrete spectrum of a finite regular graph by the continuous spectrum of an infinite regular tree. We interpret these spectra as probability distributions and the girth condition as equalities between the moments of these distributions. Then the associated orthogonal poly...

A homomorphism from an oriented graph G to an oriented graph H is an arc-preserving mapping φ from V (G) to V (H), that is φ(x)φ(y) is an arc in H whenever xy is an arc in G. The oriented chromatic number of G is the minimum order of an oriented graph H such that G has a homomorphism to H. The oriented chromatic index of G is the minimum order of an oriented graph H such that the line-digraph o...

In this paper, we give two constructions of weakly distance-regular digraphs of girth 2, and prove that certain quotient digraph of a commutative weakly distancetransitive digraph of girth 2 is a distance-transitive graph. As an application of the result, we not only give some constructions of weakly distance-regular digraphs which are not weakly distance-transitive, but determine a special cla...

In this paper we obtain (q + 3)–regular graphs of girth 5 with fewer vertices than previously known ones for q = 13, 17, 19 and for any prime q ≥ 23 performing operations of reductions and amalgams on the Levi graph Bq of an elliptic semiplane of type C. We also obtain a 13–regular graph of girth 5 on 236 vertices from B11 using the same technique.

Reed conjectured that for every > 0 and ∆ there exists g such that the fractional total chromatic number of a graph with maximum degree ∆ and girth at least g is at most ∆ + 1 + . We prove the conjecture for ∆ = 3 and for even ∆ ≥ 4 in the following stronger form: For each of these values of ∆, there exists g such that the fractional total chromatic number of any graph with maximum degree ∆ and...