2025/07/23 by Kinkar Chandra Das, Jayanta Bera, Das, Kinkar Chandra +1
Computer Science · Mathematics · #Combinatorics (math.CO) #Commutative Algebra and Its Applications #FOS: Mathematics #Mathematics and Applications #Polynomial and algebraic computation
paper · pdf · doi:10.48550/arxiv.2507.17246
openalex publication_date 2025/07/23 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/28
Recently, the Euler Sombor index (EUS) was introduced as a novel degree-based topological index. For a graph G, the Euler Sombor index is defined as EUS(G) = ∑vi vj ∈ E(G) √(di2 + dj2 + di dj), where di and dj denote the degrees of the vertices vi and vj, respectively. Very recently, Khanra and Das \textbf\bf [Euler Sombor index of trees, unicyclic and chemical graphs, MATCH Commun. Math. Comput. Chem. 94 (2025) 525--548] proposed several open problems concerning the Euler Sombor index. This paper completely resolves two of the most challenging problems posed therein. First, we determine the minimum value of the EUS index among all unicyclic graphs of a fixed order and prescribed girth, and we characterize the extremal graphs that attain this minimum. Building on this result, we further establish the minimum EUS index within the broader class of connected graphs of the same order and girth, and identify the corresponding extremal structures. In addition, we classify all connected graphs that attain the maximum Euler Sombor index (EUS) when both the order and the number of leaves are fixed.