4,335 research outputs found
The codes and the lattices of Hadamard matrices
It has been observed by Assmus and Key as a result of the complete
classification of Hadamard matrices of order 24, that the extremality of the
binary code of a Hadamard matrix H of order 24 is equivalent to the extremality
of the ternary code of H^T. In this note, we present two proofs of this fact,
neither of which depends on the classification. One is a consequence of a more
general result on the minimum weight of the dual of the code of a Hadamard
matrix. The other relates the lattices obtained from the binary code and from
the ternary code. Both proofs are presented in greater generality to include
higher orders. In particular, the latter method is also used to show the
equivalence of (i) the extremality of the ternary code, (ii) the extremality of
the Z_4-code, and (iii) the extremality of a lattice obtained from a Hadamard
matrix of order 48.Comment: 16 pages. minor revisio
Construction of quasi-cyclic self-dual codes
There is a one-to-one correspondence between -quasi-cyclic codes over a
finite field and linear codes over a ring . Using this correspondence, we prove that every
-quasi-cyclic self-dual code of length over a finite field
can be obtained by the {\it building-up} construction, provided
that char or , is a prime , and
is a primitive element of . We determine possible weight
enumerators of a binary -quasi-cyclic self-dual code of length
(with a prime) in terms of divisibility by . We improve the result of
[3] by constructing new binary cubic (i.e., -quasi-cyclic codes of length
) optimal self-dual codes of lengths (Type I), 54 and
66. We also find quasi-cyclic optimal self-dual codes of lengths 40, 50, and
60. When , we obtain a new 8-quasi-cyclic self-dual code
over and a new 6-quasi-cyclic self-dual code over
. When , we find a new 4-quasi-cyclic self-dual
code over and a new 6-quasi-cyclic self-dual code
over .Comment: 25 pages, 2 tables; Finite Fields and Their Applications, 201
Self-Dual Codes
Self-dual codes are important because many of the best codes known are of
this type and they have a rich mathematical theory. Topics covered in this
survey include codes over F_2, F_3, F_4, F_q, Z_4, Z_m, shadow codes, weight
enumerators, Gleason-Pierce theorem, invariant theory, Gleason theorems,
bounds, mass formulae, enumeration, extremal codes, open problems. There is a
comprehensive bibliography.Comment: 136 page
Coding Theory and Algebraic Combinatorics
This chapter introduces and elaborates on the fruitful interplay of coding
theory and algebraic combinatorics, with most of the focus on the interaction
of codes with combinatorial designs, finite geometries, simple groups, sphere
packings, kissing numbers, lattices, and association schemes. In particular,
special interest is devoted to the relationship between codes and combinatorial
designs. We describe and recapitulate important results in the development of
the state of the art. In addition, we give illustrative examples and
constructions, and highlight recent advances. Finally, we provide a collection
of significant open problems and challenges concerning future research.Comment: 33 pages; handbook chapter, to appear in: "Selected Topics in
Information and Coding Theory", ed. by I. Woungang et al., World Scientific,
Singapore, 201
On extremal self-dual ternary codes of length 48
All extremal ternary codes of length 48 that have some automorphism of prime
order are equivalent to one of the two known codes, the Pless code or
the extended quadratic residue code
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