1,195 research outputs found
Schubert Varieties, Linear Codes and Enumerative Combinatorics
We consider linear error correcting codes associated to higher dimensional
projective varieties defined over a finite field. The problem of determining
the basic parameters of such codes often leads to some interesting and
difficult questions in combinatorics and algebraic geometry. This is
illustrated by codes associated to Schubert varieties in Grassmannians, called
Schubert codes, which have recently been studied. The basic parameters such as
the length, dimension and minimum distance of these codes are known only in
special cases. An upper bound for the minimum distance is known and it is
conjectured that this bound is achieved. We give explicit formulae for the
length and dimension of arbitrary Schubert codes and prove the minimum distance
conjecture in the affirmative for codes associated to Schubert divisors.Comment: 12 page
Linear Codes associated to Determinantal Varieties
We consider a class of linear codes associated to projective algebraic
varieties defined by the vanishing of minors of a fixed size of a generic
matrix. It is seen that the resulting code has only a small number of distinct
weights. The case of varieties defined by the vanishing of 2 x 2 minors is
considered in some detail. Here we obtain the complete weight distribution.
Moreover, several generalized Hamming weights are determined explicitly and it
is shown that the first few of them coincide with the distinct nonzero weights.
One of the tools used is to determine the maximum possible number of matrices
of rank 1 in a linear space of matrices of a given dimension over a finite
field. In particular, we determine the structure and the maximum possible
dimension of linear spaces of matrices in which every nonzero matrix has rank
1.Comment: 12 pages; to appear in Discrete Mat
Decomposable Subspaces, Linear Sections of Grassmann Varieties, and Higher Weights of Grassmann Codes
Given a homogeneous component of an exterior algebra, we characterize those
subspaces in which every nonzero element is decomposable. In geometric terms,
this corresponds to characterizing the projective linear subvarieties of the
Grassmann variety with its Plucker embedding. When the base field is finite, we
consider the more general question of determining the maximum number of points
on sections of Grassmannians by linear subvarieties of a fixed (co)dimension.
This corresponds to a known open problem of determining the complete weight
hierarchy of linear error correcting codes associated to Grassmann varieties.
We recover most of the known results as well as prove some new results. In the
process we obtain, and utilize, a simple generalization of the Griesmer-Wei
bound for arbitrary linear codes.Comment: 16 page
Equidistant Codes in the Grassmannian
Equidistant codes over vector spaces are considered. For -dimensional
subspaces over a large vector space the largest code is always a sunflower. We
present several simple constructions for such codes which might produce the
largest non-sunflower codes. A novel construction, based on the Pl\"{u}cker
embedding, for 1-intersecting codes of -dimensional subspaces over \F_q^n,
, where the code size is is
presented. Finally, we present a related construction which generates
equidistant constant rank codes with matrices of size
over \F_q, rank , and rank distance .Comment: 16 page
Problems on q-Analogs in Coding Theory
The interest in -analogs of codes and designs has been increased in the
last few years as a consequence of their new application in error-correction
for random network coding. There are many interesting theoretical, algebraic,
and combinatorial coding problems concerning these q-analogs which remained
unsolved. The first goal of this paper is to make a short summary of the large
amount of research which was done in the area mainly in the last few years and
to provide most of the relevant references. The second goal of this paper is to
present one hundred open questions and problems for future research, whose
solution will advance the knowledge in this area. The third goal of this paper
is to present and start some directions in solving some of these problems.Comment: arXiv admin note: text overlap with arXiv:0805.3528 by other author
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