Jan 25 2007 - 2:30pm
Jan 25 2007 - 3:30pm
Erin McNicholas
Willamette University
EA 295
We examine a certain class of three-regular graphs used to represent
one-face maps. Numerical studies have revealed that the eigenvalue
statistics of these graphs are the same as those of much larger and more
widely studied classes of random matrices. If we limit our studies to
three-regular graphs representing genus zero one-face maps, the
eigenvalue statistics are strikingly different. The embedded graph of a
genus zero one-face map is a tree, and there is a correlation between
its vertices and the primitive cycles of the associated three-regular
graph. In this talk, we examine the structure and eigenvalue statistics
of these embedded planar trees. In particular, we show how the Dyck
path representation can be used to recast questions about the
probabilistic structure of random planar trees into straightforward
counting problems. Using this Dyck path approach, we find:
1. the expected number of degree k vertices adjacent to j degree d
vertices in a random planar tree,
2. the structure of the planar tree's adjacency matrix under a natural
labeling of the vertices, and
3. an explanation for the existence of eigenvalues with multiplicity
greater than one in the tree's spectrum.