1,259 research outputs found
New proofs of the Assmus-Mattson theorem based on the Terwilliger algebra
We use the Terwilliger algebra to provide a new approach to the
Assmus-Mattson theorem. This approach also includes another proof of the
minimum distance bound shown by Martin as well as its dual.Comment: 15 page
A duality between pairs of split decompositions for a Q-polynomial distance-regular graph
AbstractLet Γ denote a Q-polynomial distance-regular graph with diameter D≥3 and standard module V. Recently, Ito and Terwilliger introduced four direct sum decompositions of V; we call these the (μ,ν)-split decompositions of V, where μ,ν∈{↓,↑}. In this paper we show that the (↓,↓)-split decomposition and the (↑,↑)-split decomposition are dual with respect to the standard Hermitian form on V. We also show that the (↓,↑)-split decomposition and the (↑,↓)-split decomposition are dual with respect to the standard Hermitian form on V
A -polynomial structure associated with the projective geometry
There is a type of distance-regular graph, said to be -polynomial. In this
paper we investigate a generalized -polynomial property involving a graph
that is not necessarily distance-regular. We give a detailed description of an
example associated with the projective geometry .Comment: 21 page
Commutative association schemes
Association schemes were originally introduced by Bose and his co-workers in
the design of statistical experiments. Since that point of inception, the
concept has proved useful in the study of group actions, in algebraic graph
theory, in algebraic coding theory, and in areas as far afield as knot theory
and numerical integration. This branch of the theory, viewed in this collection
of surveys as the "commutative case," has seen significant activity in the last
few decades. The goal of the present survey is to discuss the most important
new developments in several directions, including Gelfand pairs, cometric
association schemes, Delsarte Theory, spin models and the semidefinite
programming technique. The narrative follows a thread through this list of
topics, this being the contrast between combinatorial symmetry and
group-theoretic symmetry, culminating in Schrijver's SDP bound for binary codes
(based on group actions) and its connection to the Terwilliger algebra (based
on combinatorial symmetry). We propose this new role of the Terwilliger algebra
in Delsarte Theory as a central topic for future work.Comment: 36 page
Distance-regular graphs
This is a survey of distance-regular graphs. We present an introduction to
distance-regular graphs for the reader who is unfamiliar with the subject, and
then give an overview of some developments in the area of distance-regular
graphs since the monograph 'BCN' [Brouwer, A.E., Cohen, A.M., Neumaier, A.,
Distance-Regular Graphs, Springer-Verlag, Berlin, 1989] was written.Comment: 156 page
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