A new approach to solving three combinatorial enumeration problems on planar graphs Original Research Article

The purpose of this paper is to show how the technique of delta-wye graph reduction provides an alternative method for solving three enumerative function evaluation problems on planar graphs. In particular, it is shown how to compute the number of spanning trees and perfect matchings, and how to evaluate energy in the Ising “spin glass” model of statistical mechanics. These alternative algorithms require O(n2) arithmetic operations on an n-vertex planar grapha, and are relatively easy to implement.