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Let G be a graph containing no isolated vertices. For the graph G, its modified first Zagreb index is defined as the sum of reciprocals of squares of vertex degrees of G. This article provides some new bounds on the modified first Zagreb index of G in terms of some other well-known graph invariants of G. From the obtained bounds, several known results follow directly. [ABSTRACT FROM AUTHOR]

Let G = (V;E), V = fv1; v2;:::; vng, be a simple connected graph with n vertices, m edges and a sequence of vertex degrees d1 d2 dn > 0, di = d(vi). Let A = (aij)nn and D = diag(d1; d2;:::; dn) be the adjacency and the diagonal degree matrix of G, respectively. Denote by L+(G) = D-1=2(D + A)D-1=2 the normalized signless Laplacian matrix of graph G. The eigenvalues of matrix L+(G), 2 = + 1 + 2 = + n = 0, are normalized signless Laplacian eigenvalues of G. In this paper some bounds for the sum K+(G) = Pn i=1 1 + i are considered. [ABSTRACT FROM AUTHOR]

A general inequality for non-negative real numbers is proven. Based on it, upper bounds for (ordinary) graph energy, minimum dominating energy, minimum covering energy, Laplacian-energy-like invariant, Laplacian energy, Randić energy, and incidence energy are obtained. [ABSTRACT FROM AUTHOR]

Let G be an undirected simple and connected graph with n vertices .n ≥ 3/ and m edges. Denote by μ1 ≥ μ2 ≥ ... ≥ μn-1 > μn = 0, γ1 ≥ γ2 ≥ ... ≥ γn, and ρ1 ≥ ρ2 ≥ ... ≥ ρn-1 > ρn = 0, respectively, the Laplacian, signless Laplacian, and normalized Laplacian eigenvalues of G. The Laplacian energy, signless Laplacian energy, and normalized Laplacian energy of G are defined as LE = Σn i=1/μi - 2m/n/, SLE = Σni=1/γi - 2m/n/, and NLE =Σni=1/ρi -1/, respectively. Lower bounds for LE, SLE, and NLE are obtained. [ABSTRACT FROM AUTHOR]

Let G = ( V , E ) be a simple graph of order n and size m , with vertex set V ( G ) = { v 1 , v 2 , … , v n } , without isolated vertices and sequence of vertex degrees Δ = d 1 ≥ d 2 ≥ ⋯ ≥ d n = δ > 0 , d i = d G ( v i ) . If the vertices v i and v j are adjacent, we denote it as v i v j ∈ E ( G ) or i ∼ j . With TI we denote a topological index that can be represented as T I = T I ( G ) = ∑ i ∼ j F ( d i , d j ) , where F is an appropriately chosen function with the property F ( x , y ) = F ( y , x ) . A general extended adjacency matrix A = ( a i j ) of G is defined as a i j = F ( d i , d j ) if the vertices v i and v j are adjacent, and a i j = 0 otherwise. Denote by f i , i = 1 , 2 , … , n the eigenvalues of A . The “energy” of the general extended adjacency matrix is defined as E T I = E T I ( G ) = ∑ i = 1 n | f i | . Lower and upper bounds on E T I are obtained. By means of the present approach a plethora of earlier established results can be obtained as special cases. [ABSTRACT FROM AUTHOR]

Two weighted inequalities for real non-negative sequences are proven. The first one represents a generalization of the Szőkefalvi Nagy inequality for the variance, and the second a generalization of the discrete Chebyshev inequality for two real sequences. Then, the obtained inequalities are used to determine lower bounds for some degree-based topological indices of graphs. [ABSTRACT FROM AUTHOR]