Abstract:In this paper, we present some upper bounds for the number of spanning trees of graphs in terms of the number of vertices, the number of edges and the vertex degrees. MSC: 05C05; 05C50
The problems of maximizing the spectral radius and the number of spanning trees in a class of bipartite graphs with certain degree constraints are considered. In both the problems, the optimal graph is conjectured to be a Ferrers graph. Known results towards the resolution of the conjectures are described. We give yet another proof of a formula due to Ehrenborg and van Willigenburg for the number of spanning trees in a Ferrers graph. The main tool is a result which gives several necessary and sufficient conditions under which the removal of an edge in a graph does not affect the resistance distance between the end-vertices of another edge.
The problems of maximizing the spectral radius and the number of spanning trees in a class of bipartite graphs with certain degree constraints are considered. In both the problems, the optimal graph is conjectured to be a Ferrers graph. Known results towards the resolution of the conjectures are described. We give yet another proof of a formula due to Ehrenborg and van Willigenburg for the number of spanning trees in a Ferrers graph. The main tool is a result which gives several necessary and sufficient conditions under which the removal of an edge in a graph does not affect the resistance distance between the end-vertices of another edge.
“…The key idea behind the bound above is to apply the AM-GM inequality to the normalized eigenvalues. Other recent advances in constructing upper bounds for the number of spanning trees can be found in [9], another overview is given in [8].…”
Section: Introductionmentioning
confidence: 99%
“…Though, for a bipartite graph we know some improvement of the bound (1) . For example, in [8] the following upper bound was shown for a bipartite connected graph…”
In this paper, we address the Ehrenborg's conjecture which proposes that for any bipartite graph G the inequality τ (G) ≤ m −1 n −1 D(G) holds. Here τ (G) denotes the number of spanning trees of G, D(G) is the product of the degrees of the vertices and m, n are the sizes of the components. We show that the conjecture is true for a one-side regular graph (that is a graph for which all degrees of the vertices of at least one of the components are equal). We also present a proof alternative to one given in [7] of the fact that the equality holds for Ferrers graphs.
“…Now, we give some known upper bounds on t ( G ): Grimmett [ 11 ]: Grone and Merris [ 12 ]: Nosal [ 13 ]: for r -regular graphs, Cvetković et al (see [ 5 , page 222]): where is the number of edges of , Das [ 14 ]: Zhang [ 15 ]: where a = (( n ( n −1) − 2 m )/2 mn ( n −2)) 1/2 , Feng et al [ 16 ]: Li et al [ 17 ]: Bozkurt [ 18 ]: where b = (( n −1−Δ 1 )/ n ( n −2)Δ 1 ) 1/2 , Das et al [ 19 ]: …”
Section: Introductionmentioning
confidence: 99%
“…However, Das et al [ 19 ] proved that ( 11 ) is not true for K n . In [ 15 , 16 , 18 ] the authors showed that ( 8 ) is better than ( 3 ), ( 9 ) is better than ( 7 ) and ( 10 ), and ( 12 ) is better than ( 4 ). For more bounds and the relations between the number of spanning trees and the structural parameters of graphs such as connectivity, chromatic number, independence number, and clique number, see [ 17 , 19 ].…”
We establish some bounds for the number of spanning trees of connected graphs in terms of the number of vertices (n), the number of edges (m), maximum vertex degree (Δ1), minimum vertex degree (δ), first Zagreb index (M
1), and Randić index (R
−1).
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