1,717 research outputs found
Extensions of Barrier Sets to Nonzero Roots of the Matching Polynomials
In matching theory, barrier sets (also known as Tutte sets) have been studied
extensively due to its connection to maximum matchings in a graph. In this
paper, we first define -barrier sets. Our definition of a
-barrier set is slightly different from that of a barrier set. However
we show that -barrier sets and barrier sets have similar properties. In
particular, we prove a generalized Berge's Formula and give a characterization
for the set of all -special vertices in a graph
Average mixing of continuous quantum walks
If is a graph with adjacency matrix , then we define to be the
operator . The Schur (or entrywise) product is a
doubly stochastic matrix and, because of work related to quantum computing, we
are concerned the \textsl{average mixing matrix}. This can be defined as the
limit of C^{-1} \int_0^C H(t)\circ H(-t)\dt as . We establish
some of the basic properties of this matrix, showing that it is positive
semidefinite and that its entries are always rational. We find that for paths
and cycles this matrix takes on a surprisingly simple form, thus for the path
it is a linear combination of , (the all-ones matrix), and a permutation
matrix.Comment: 20 pages, minor fixes, added section on discrete walks; fixed typo
When can perfect state transfer occur?
Let be a graph on vertices with with adjacency matrix and let
denote the matrix-valued function . If and are
distinct vertices in , we say perfect state transfer from to occurs
if there is a time such that . Our chief problem
is to characterize the cases where perfect state transfer occurs. We show that
if perfect state transfer does occur in a graph, then the spectral radius is an
integer or a quadratic irrational; using this we prove that there are only
finitely many graphs with perfect state transfer and with maximum valency at
most 4K4. We also show that if perfect state transfer from to occurs,
then the graphs and are cospectral and any
automorphism of that fixes must fix (and conversely).Comment: 16 page
Bose-Mesner Algebras attached to Invertible Jones Pairs
In 1989, Vaughan Jones introduced spin models and showed that they could be
used to form link invariants in two different ways--by constructing
representations of the braid group, or by constructing partition functions.
These spin models were subsequently generalized to so-called 4-weight spin
models by Bannai and Bannai; these could be used to construct partition
functions, but did not lead to braid group representations in any obvious way.
Jaeger showed that spin models were intimately related to certain association
schemes. Yamada gave a construction of a symmetric spin model on vertices
from each 4-weight spin model on vertices.
In this paper we build on recent work with Munemasa to give a different proof
to Yamada's result, and we analyse the structure of the association scheme
attached to this spin model.Comment: 23 page
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