On the number of independent subsets in trees with restricted degrees

  • Authors:
  • Eric Ould Dadah Andriantiana;Stephan Wagner

  • Affiliations:
  • -;-

  • Venue:
  • Mathematical and Computer Modelling: An International Journal
  • Year:
  • 2011

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Abstract

We study the number of independent vertex subsets (known as the Merrifield-Simmons index in mathematical chemistry) and the number of independent edge subsets (called the Hosoya index) for trees whose vertex degrees are restricted to 1 or d (for some d=3), a natural restriction in the chemical context. We find that the minimum of the Merrifield-Simmons index and the maximum of the Hosoya index are both attained for path-like trees; furthermore, one obtains the second-smallest value of the Merrifield-Simmons index and the second-largest value of the Hosoya index for generalized tripods. Analogous results are also found for a closely related parameter, the graph energy, which also plays an important role in mathematical chemistry.