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A note on radio antipodal colourings of paths

Riadh Khennoufa, Olivier Togni (2005)

Mathematica Bohemica

The radio antipodal number of a graph G is the smallest integer c such that there exists an assignment f V ( G ) → { 1 , 2 , ... , c } satisfying | f ( u ) - f ( v ) | ≥ D - d ( u , v ) for every two distinct vertices u and v of G , where D is the diameter of G . In this note we determine the exact value of the antipodal number of the path, thus answering the conjecture given in [G. Chartrand, D. Erwin and P. Zhang, Math. Bohem. 127 (2002), 57–69]. We also show the connections between this colouring and radio labelings.

A note on solvable vertex stabilizers of s -transitive graphs of prime valency

Song-Tao Guo, Hailong Hou, Yong Xu (2015)

Czechoslovak Mathematical Journal

A graph X , with a group G of automorphisms of X , is said to be ( G , s ) -transitive, for some s ≥ 1 , if G is transitive on s -arcs but not on ( s + 1 ) -arcs. Let X be a connected ( G , s ) -transitive graph of prime valency p ≥ 5 , and G v the vertex stabilizer of a vertex v ∈ V ( X ) . Suppose that G v is solvable. Weiss (1974) proved that | G v | ∣ p ( p - 1 ) 2 . In this paper, we prove that G v ≅ ( ℤ p ⋊ ℤ m ) × ℤ n for some positive integers m and n such that n div m and m ∣ p - 1 .

A note on strong and co-strong perfectness of the X-join of graphs

Alina Szelecka, Andrzej Włoch (1996)

Discussiones Mathematicae Graph Theory

Strongly perfect graphs were introduced by C. Berge and P. Duchet in [1]. In [4], [3] the following was studied: the problem of strong perfectness for the Cartesian product, the tensor product, the symmetrical difference of n, n ≥ 2, graphs and for the generalized Cartesian product of graphs. Co-strong perfectness was first studied by G. Ravindra andD. Basavayya [5]. In this paper we discuss strong perfectness and co-strong perfectness for the generalized composition (the lexicographic product)...

A note on strongly multiplicative graphs

Chandrashekar Adiga, H.N. Ramaswamy, D.D. Somashekara (2004)

Discussiones Mathematicae Graph Theory

In this note we give an upper bound for λ(n), the maximum number of edges in a strongly multiplicative graph of order n, which is sharper than the upper bound obtained by Beineke and Hegde [1].

A note on the Chvátal-rank of clique family inequalities

Arnaud Pêcher, Annegret K. Wagler (2007)

RAIRO - Operations Research


Clique family inequalities a∑v∈W xv + (a - 1)∈v∈W, xv ≤ aδ form an intriguing class of valid inequalities for the stable set polytopes of all graphs. We prove firstly that their Chvátal-rank is at most a, which provides an alternative proof for the validity of clique family inequalities, involving only standard rounding arguments. Secondly, we strengthen the upper bound further and discuss consequences regarding the Chvátal-rank of subclasses of claw-free graphs.


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