Enumerating Perfect Matchings in Inductively-Defined Families of Graphs

J. C. George1, W. D. Wallis2
1Department of Mathematics and Natural Sciences, Gordon College, Barnesville, GA 30204 USA
2Department of Mathematics, Southern Illinois University, Carbondale, IL 62901 USA.

Abstract

In this paper, we look at families \(\{G_n\}\) of graphs (for \(n > 0\)) for which the number of perfect matchings of \(G_n\) is the \(n\)th term in a sequence of generalized Fibonacci numbers. A one-factor of a graph is a set of edges forming a spanning one-regular subgraph (a perfect matching). The generalized Fibonacci numbers are the integers produced by a two-term homogeneous linear recurrence from given initial values. We explore the construction of such families of graphs, using as our motivation the \emph{Ladder Graph} \(L_n\); it is well-known that \(L_n\) has exactly \(F_{n+1}\) perfect matchings, where \(F_n\) is the traditional Fibonacci sequence, defined by \(F_1 = F_2 = 1\), and \(F_{n+1} = F_n + F_{n-1}\).