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arXiv 1811.09142cs.ITmath.COmath.IT
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最优局部可恢复码的构造及其与超图的联系

Construction of optimal locally recoverable codes and connection with hypergraph

Chaoping Xing, Chen Yuan

摘要:

最近,几位作者发现,$q$元最优局部可恢复代码,即,归档Singleton类型界限的本地可恢复代码可以具有比$q+1$大得多的长度。这与经典的$q$元MDS码有很大的不同,在经典的MDS码中,证明了码长的上界为$q+1$(或在某些特殊情况下为$q+2$)。这一发现启发了最近一些关于最佳本地可恢复代码长度的研究。\cite{LXY}证明了对于$d=3,4$,$q$元最优局部可恢复代码是无界的.随后证明了具有距离$d$和局部性$r$的$q$元最优局部可恢复码的长度为$Ω_{d,r}(q^{1 + 1/\lfloor(d-3)/2\rfloor})$。最近,在\cite{J18}和\cite{BCGLP}中给出了距离$d=5,6$的$q$元最优局部可恢复码的显式构造.在本文中,我们进一步研究构造最优局部可恢复码沿线使用奇偶校验矩阵。受经典的Reed-Solomon码和\cite{J18}的启发,我们给校验矩阵赋予了Vandermond结构。结果表明,具有Vandermond结构的校验矩阵产生的最优局部可恢复码必须满足$\mathbb{F}_q$子集的不交性。令我们惊讶的是,这个不相交条件等价于极值图论中一个研究得很好的问题。借助于极值图论,我们成功地将\cite{GXY}中的所有著名结果推广到了$d\geq 7$ .此外,对于$d=6$,我们能够去除在\cite{J18}中要求的$q$是偶数的约束。

英文摘要:

Recently, it was discovered by several authors that a $q$-ary optimal locally recoverable code, i.e., a locally recoverable code archiving the Singleton-type bound, can have length much bigger than $q+1$. This is quite different from the classical $q$-ary MDS codes where it is conjectured that the code length is upper bounded by $q+1$ (or $q+2$ for some special case). This discovery inspired some recent studies on length of an optimal locally recoverable code. It was shown in \cite{LXY} that a $q$-ary optimal locally recoverable code is unbounded for $d=3,4$. Soon after, it was proved that a $q$-ary optimal locally recoverable code with distance $d$ and locality $r$ can have length $Ω_{d,r}(q^{1 + 1/\lfloor(d-3)/2\rfloor})$. Recently, an explicit construction of $q$-ary optimal locally recoverable codes for distance $d=5,6$ was given in \cite{J18} and \cite{BCGLP}. In this paper, we further investigate construction optimal locally recoverable codes along the line of using parity-check matrices. Inspired by classical Reed-Solomon codes and \cite{J18}, we equip parity-check matrices with the Vandermond structure. It is turns out that a parity-check matrix with the Vandermond structure produces an optimal locally recoverable code must obey certain disjoint property for subsets of $\mathbb{F}_q$. To our surprise, this disjoint condition is equivalent to a well-studied problem in extremal graph theory. With the help of extremal graph theory, we succeed to improve all of the best known results in \cite{GXY} for $d\geq 7$. In addition, for $d=6$, we are able to remove the constraint required in \cite{J18} that $q$ is even.

机构、总结、中文摘要均由AI分析而来,可能存在错误,请以论文正文为准。

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