Hua, Hongbo; Zhang, Shenggui On the reciprocal degree distance of graphs. (English) Zbl 1242.05060 Discrete Appl. Math. 160, No. 7-8, 1152-1163 (2012). Summary: We study a new graph invariant named reciprocal degree distance (RDD), defined for a connected graph \(G\) as vertex-degree Wikipedia Wolfram MathWorld -weighted sum of the reciprocal distances, that is, \[ RDD(G)=\sum_{\{u,v\}\subset V(G)}(d_{G}(u)+d_{G}(v)) \frac {1}{d_{G}(u,v)} \] . The reciprocal degree distance is a weight version of the Harary index, just as the degree distance is a weight version of the Wiener index Wikipedia Wolfram MathWorld . Our main purpose is to investigate extremal properties of reciprocal degree distance. We first characterize among all nontrivial connected graphs of given order the graphs with the maximum and minimum reciprocal degree distance, respectively. Then we characterize the nontrivial connected graph with given order, size and the maximum reciprocal degree distance as well as the tree, unicyclic graph Wikipedia Wikipedia Wolfram MathWorld Wolfram MathWorld and cactus with the maximum reciprocal degree distance, respectively. Finally, we establish various lower and upper bounds for the reciprocal degree distance in terms of other graph invariants including the degree distance, Harary index, the first Zagreb index, the first Zagreb coindex, pendent vertices, independence number Wikipedia Wikipedia Wolfram MathWorld Wolfram MathWorld , chromatic number and vertex-, and edge-connectivity Wikipedia Wikipedia Wolfram MathWorld Wolfram MathWorld .© Elsevier B.V. Cited in 2 ReviewsCited in 35 Documents MSC: 05C07 Vertex degrees 05C12 Distance in graphs 05C35 Extremal problems in graph theory Keywords:distance (in graphs); degree distance; reciprocal degree distance; bounds; extremal graphs × Cite Format Result Cite Review PDF Full Text: DOI References: [1] Ashrafi, A. R.; Došlić, T.; Hamzeha, A., The Zagreb coindices of graph operations, Discrete Appl. Math., 158, 1571-1578, 2010 · Zbl 1201.05100 [2] Ashrafi, A. R.; Došlić, T.; Hamzeha, A., Extremal graphs with respect to the Zagreb coindices, MATCH Commun. Math. Comput. Chem., 65, 85-92, 2011 · Zbl 1265.05135 [3] Bondy, J. A.; Murty, U. S.R., Graph Theory with Applications, 1976, Macmillan London and Elsevier: Macmillan London and Elsevier New York · Zbl 1226.05083 [4] Bucicovschia, O.; Cioabaˇ, S. M., The minimum degree distance of graphs of given order and size, Discrete Appl. Math., 156, 3518-3521, 2008 · Zbl 1168.05308 [5] Dankelmann, P.; Gutman, I.; Mukwembi, S.; Swart, H. 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