15 research outputs found
Perfect single error-correcting codes in the Johnson Scheme
Delsarte conjectured in 1973 that there are no nontrivial pefect codes in the
Johnson scheme. Etzion and Schwartz recently showed that perfect codes must be
k-regular for large k, and used this to show that there are no perfect codes
correcting single errors in J(n,w) for n <= 50000. In this paper we show that
there are no perfect single error-correcting codes for n <= 2^250.Comment: 4 pages, revised, accepted for publication in IEEE Transactions on
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Some Bounds for the Number of Blocks III
Let be a pair of point set and
a set consists of point subsets of which are called
blocks. Let be the maximal cardinality of the intersections between the
distinct two blocks in . The triple is called the
parameter of . Let be the number of the blocks in .
It is shown that inequality
holds for each satisfying , in the paper: Some Bounds for
the Number of Blocks, Europ. J. Combinatorics 22 (2001), 91--94, by R. Noda. If
achieves the upper bound, is called a design. In
the paper, an upper bound and a lower bound, , for of a design are
given. In the present paper we consider the cases when does not achieve the
upper bound or lower bound given above, and get new more strict bounds for
respectively. We apply this bound to the problem of the perfect -codes in
the Johnson scheme, and improve the bound given by Roos in 1983.Comment: Stylistic corrections are made. References are adde
New Constant-Weight Codes from Propagation Rules
This paper proposes some simple propagation rules which give rise to new
binary constant-weight codes.Comment: 4 page
Cocyclic simplex codes of type alpha over Z4 and Z2s
Over the past decade, cocycles have been used to construct Hadamard and generalized Hadamard matrices. This, in turn, has led to the construction of codes-self-dual and others. Here we explore these ideas further to construct cocyclic complex and Butson-Hadamard matrices, and subsequently we use the matrices to construct simplex codes of type /spl alpha/ over Z(4) and Z(2/sup s/), respectively
On the binary linear constant weight codes and their autormorphism groups
We give a characterization for the binary linear constant weight codes by
using the symmetric difference of the supports of the codewords. This
characterization gives a correspondence between the set of binary linear
constant weight codes and the set of partitions for the union of supports of
the codewords. By using this correspondence, we present a formula for the order
of the automorphism group of a binary linear constant weight code in terms of
its parameters. This formula is a key step to determine more algebraic
structures on constant weight codes with given parameters. Bonisoli [Bonisoli,
A.: Every equidistant linear code is a sequence of dual Hamming codes. Ars
Combinatoria 18, 181--186 (1984)] proves that the -ary linear constant
weight codes with the same parameters are equivalent (for the binary case
permutation equivalent). We also give an alternative proof for Bonisoli's
theorem by presenting an explicit permutation on symmetric difference of the
supports of the codewords which gives the permutation equivalence between the
binary linear constant weight codes.Comment: 12 page