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Let G be a simple connected graph with n vertices, and let d i be the degree of the vertex v i in G. The extended adjacency matrix of G is defined so that the ij-entry is 1 2if the vertices v i and v j are adjacent in G, and 0 otherwise. This matrix was originally introduced for developing novel topological indices used in the QSPR/QSAR studies. In this paper, we consider extremal problems of the largest eigenvalue of the extended adjacency matrix (also known as the extended spectral radius) of trees. We show that among all trees of order n ≥ 5, the path P n (resp., the star S n ) uniquely minimizes (resp., maximizes) the extended spectral radius. We also determine the first five trees with the maximal extended spectral radius.
Let G be a simple connected graph with n vertices, and let d i be the degree of the vertex v i in G. The extended adjacency matrix of G is defined so that the ij-entry is 1 2if the vertices v i and v j are adjacent in G, and 0 otherwise. This matrix was originally introduced for developing novel topological indices used in the QSPR/QSAR studies. In this paper, we consider extremal problems of the largest eigenvalue of the extended adjacency matrix (also known as the extended spectral radius) of trees. We show that among all trees of order n ≥ 5, the path P n (resp., the star S n ) uniquely minimizes (resp., maximizes) the extended spectral radius. We also determine the first five trees with the maximal extended spectral radius.
Topological indices are an important method for understanding the fundamental topology of chemical structures. Quantitative structure properties relationship (QSPR) is an analytical approach for breaking down a molecule into a sequence of numerical values that describe the chemical and physical characteristics of the molecule. In this article, we have developed the QSPR analysis between eigenvalue‐based topological indices and physical properties of COVID‐19 drugs to predict the significance level of eigenvalue based indices. We have to use MATLAB for the computation of indices and SPSS for analysis. We show that positive interia index, signless Laplacian Estrada index and Randić energy are the best predictors of molar reactivity, polar surface area and molecular weight, respectively.
Let G 1 ∘ G 2 be the corona of two graphs G 1 and G 2 which is the graph obtained by taking one copy of G 1 and V G 1 copies of G 2 and then joining the i th vertex of G 1 to every vertex in the i th copy of G 2 . The atom-bond connectivity index (ABC index) of a graph G is defined as A B C G = ∑ u v ∈ E G d G u + d G v − 2 / d G u d G v , where E G is the edge set of G and d G u and d G v are degrees of vertices u and v , respectively. For the ABC indices of G 1 ∘ G 2 with G 1 and G 2 being connected graphs, we get the following results. (1) Let G 1 and G 2 be connected graphs. The ABC index of G 1 ∘ G 2 attains the maximum value if and only if both G 1 and G 2 are complete graphs. If the ABC index of G 1 ∘ G 2 attains the minimum value, then G 1 and G 2 must be trees. (2) Let T 1 and T 2 be trees. Then, the ABC index of T 1 ∘ T 2 attains the maximum value if and only if T 1 is a path and T 2 is a star.
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