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Paper   IPM / M / 18021
School of Mathematics
  Title:   Combinatorial upper bounds for the smallest eigenvalue of a graph
  Author(s):  Sara Saeedi Madani (Joint with A. Esmailpour and D. Kiani)
  Status:   Published
  Journal: Archiv der Mathematik
  Vol.:  123
  Year:  2024
  Pages:   29-38
  Supported by:  IPM
  Abstract:
Let G be a graph, and let λ(G) denote the smallest eigenvalue of G. First, we provide an upper bound for λ(G) based on induced bipartite subgraphs of G. Consequently, we extract two other upper bounds, one relying on the average degrees of induced bipartite subgraphs and a more explicit one in terms of the chromatic number and the independence number of G. In particular, motivated by our bounds, we introduce two graph invariants that are of interest on their own. Finally, special attention goes to the investigation of the sharpness of our bounds in various classes of graphs as well as the comparison with an existing well-known upper bound.

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