87 research outputs found
Automorphisms of order 2p in binary self-dual extremal codes of length a multiple of 24
Let C be a binary self-dual code with an automorphism g of order 2p, where p is an odd prime, such that gp is a fixed point free involution. If C is extremal of length a multiple of 24, all the involutions are fixed point free, except the Golay Code and eventually putative codes of length 120. Connecting module theoretical properties of a self-dual code C with coding theoretical ones of the subcode C(gp) which consists of the set of fixed points of gp, we prove that C is a projective F2g module if and only if a natural projection of C(gp) is a self-dual code. We then discuss easy-to-handle criteria to decide if C is projective or not. As an application, we consider in the last part extremal self-dual codes of length 120, proving that their automorphism group does not contain elements of order 38 and 58. © 1963-2012 IEEE
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
Some new results on the self-dual [120,60,24] code
The existence of an extremal self-dual binary linear code of length 120 is a
long-standing open problem. We continue the investigation of its automorphism
group, proving that automorphisms of order 30 and 57 cannot occur. Supposing
the involutions acting fixed point freely, we show that also automorphisms of
order 8 cannot occur and the automorphism group is of order at most 120, with
further restrictions. Finally, we present some necessary conditions for the
existence of the code, based on shadow and design theory.Comment: 23 pages, 6 tables, to appear in Finite Fields and Their Application
Hadamard matrices of orders 60 and 64 with automorphisms of orders 29 and 31
A classification of Hadamard matrices of order with an automorphism of
order is given for and . The ternary self-dual codes spanned by
the newly found Hadamard matrices of order with an automorphism of order
are computed, as well as the binary doubly even self-dual codes of length
with generator matrices defined by related Hadamard designs. Several new
ternary near-extremal self-dual codes, as well as binary near-extremal doubly
even self-dual codes with previously unknown weight enumerators are found.Comment: 21 page
On the Structure of the Linear Codes with a Given Automorphism
The purpose of this paper is to present the structure of the linear codes
over a finite field with q elements that have a permutation automorphism of
order m. These codes can be considered as generalized quasi-cyclic codes.
Quasi-cyclic codes and almost quasi-cyclic codes are discussed in detail,
presenting necessary and sufficient conditions for which linear codes with such
an automorphism are self-orthogonal, self-dual, or linear complementary dual
Sobre automorfismos de códigos extremales de tipo II
En el presente artículo se muestran algunas técnicas para obtener tipos de automorfismos de los códigos binarios auto-duales, doblemente pares y extremales, también denominados extremales de tipo II, con parámetros [24, 12, 8], [48, 24, 12] y [120, 60, 24]. El objetivo central es obtener información sobre el correspondiente grupo de automorfismos a partir de la exclusión de algunos números primos de su orde
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