Counting Spanning Trees on Fractal Graphs

Abstract

Using the method of spectral decimation and a modified version of Kirchhoffs Matrix-Tree Theorem, a closed form solution to the number of spanning trees on approximating graphs to a fully symmetric self-similar structure on a finitely ramified fractal is given in Theorem (3.4). Examples calculated include the Sierpinski Gasket, a non p.c.f. analog of the Sierpinski Gasket, the Diamond fractal, and the Hexagasket. For each example, the asymptotic complexity constant is found. Dropping the fully symmetry assumption, it is shown that the limsup and liminf of the asymptotic complexity constant exist.