1,021 research outputs found
Association schemes related to universally optimal configurations, Kerdock codes and extremal Euclidean line-sets
H. Cohn et. al. proposed an association scheme of 64 points in R^{14} which
is conjectured to be a universally optimal code. We show that this scheme has a
generalization in terms of Kerdock codes, as well as in terms of maximal real
mutually unbiased bases. These schemes also related to extremal line-sets in
Euclidean spaces and Barnes-Wall lattices. D. de Caen and E. R. van Dam
constructed two infinite series of formally dual 3-class association schemes.
We explain this formal duality by constructing two dual abelian schemes related
to quaternary linear Kerdock and Preparata codes.Comment: 16 page
Optimality and uniqueness of the Leech lattice among lattices
We prove that the Leech lattice is the unique densest lattice in R^24. The
proof combines human reasoning with computer verification of the properties of
certain explicit polynomials. We furthermore prove that no sphere packing in
R^24 can exceed the Leech lattice's density by a factor of more than
1+1.65*10^(-30), and we give a new proof that E_8 is the unique densest lattice
in R^8.Comment: 39 page
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
Semidefinite programming, multivariate orthogonal polynomials, and codes in spherical caps
We apply the semidefinite programming approach developed in
arxiv:math.MG/0608426 to obtain new upper bounds for codes in spherical caps.
We compute new upper bounds for the one-sided kissing number in several
dimensions where we in particular get a new tight bound in dimension 8.
Furthermore we show how to use the SDP framework to get analytic bounds.Comment: 15 pages, (v2) referee comments and suggestions incorporate
Note on cubature formulae and designs obtained from group orbits
In 1960, Sobolev proved that for a finite reflection group G, a G-invariant
cubature formula is of degree t if and only if it is exact for all G-invariant
polynomials of degree at most t. In this paper, we find some observations on
invariant cubature formulas and Euclidean designs in connection with the
Sobolev theorem. First, we give an alternative proof of theorems by Xu (1998)
on necessary and sufficient conditions for the existence of cubature formulas
with some strong symmetry. The new proof is shorter and simpler compared to the
original one by Xu, and moreover gives a general interpretation of the
analytically-written conditions of Xu's theorems. Second, we extend a theorem
by Neumaier and Seidel (1988) on Euclidean designs to invariant Euclidean
designs, and thereby classify tight Euclidean designs obtained from unions of
the orbits of the corner vectors. This result generalizes a theorem of Bajnok
(2007) which classifies tight Euclidean designs invariant under the Weyl group
of type B to other finite reflection groups.Comment: 18 pages, no figur
Unitary designs and codes
A unitary design is a collection of unitary matrices that approximate the
entire unitary group, much like a spherical design approximates the entire unit
sphere. In this paper, we use irreducible representations of the unitary group
to find a general lower bound on the size of a unitary t-design in U(d), for
any d and t. We also introduce the notion of a unitary code - a subset of U(d)
in which the trace inner product of any pair of matrices is restricted to only
a small number of distinct values - and give an upper bound for the size of a
code of degree s in U(d) for any d and s. These bounds can be strengthened when
the particular inner product values that occur in the code or design are known.
Finally, we describe some constructions of designs: we give an upper bound on
the size of the smallest weighted unitary t-design in U(d), and we catalogue
some t-designs that arise from finite groups.Comment: 25 pages, no figure
Bounds on sets with few distances
We derive a new estimate of the size of finite sets of points in metric
spaces with few distances. The following applications are considered:
(1) we improve the Ray-Chaudhuri--Wilson bound of the size of uniform
intersecting families of subsets;
(2) we refine the bound of Delsarte-Goethals-Seidel on the maximum size of
spherical sets with few distances;
(3) we prove a new bound on codes with few distances in the Hamming space,
improving an earlier result of Delsarte.
We also find the size of maximal binary codes and maximal constant-weight
codes of small length with 2 and 3 distances.Comment: 11 page
Inversion of Toeplitz operators, Levinson equations, and Gohberg-Krein factorization—A simple and unified approach for the rational case
AbstractThe problem of the inversion of the Toeplitz operator TΦ, associated with the operator-valued function Φ defined on the unit circle, is known to involve the associated Levinson system of equations and the Gohberg-Krein factorization of Φ. A simplified and self-contained approach, making clear the connections between these three problems, is presented in the case where Φ is matrix-valued and rational. The key idea consists in looking at the Levinson system of equations associated with Φ−1(z−1), rather than that associated with Φ(z). As a consequence, a new invertibility criterion for Toeplitz operators with rational matrix-valued symbols is derived
Szego asymptotics for matrix-valued measures with countably many bound states
Let be a matrix-valued measure with the essential spectrum a single
interval and countably many point masses outside of it. Under the assumption
that the absolutely continuous part of satisfies Szego's condition and
the point masses satisfy a Blaschke-type condition, we obtain the asymptotic
behavior of the orthonormal polynomials on and off the support of the measure.
The result generalizes the scalar analogue of Peherstorfer-Yuditskii and the
matrix-valued result of Aptekarev-Nikishin, which handles only a finite number
of mass points
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
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