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arXiv 2009.04553cs.ITcs.DMmath.COmath.IT
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随机码性质的阈值速率

Threshold rates for properties of random codes

Venkatesan Guruswami, Jonathan Mosheiff, Nicolas Resch, Shashwat Silas, Mary Wootters

AI总结:

本研究刻画了一类由对称码字集合包含关系定义的随机码性质的阈值速率,证明其等于一阶矩下界,同时确定了特定性质的阈值速率,给出列恢复的紧界与高效估计算法。

摘要:

假设$P$是随机码$C \subset Σ^n$可能满足的一种性质。例如,对于某个$p \in (0,1)$,$P$可以是“存在$C$中的三个元素落在某个半径为$pn$的汉明球内”的性质。我们称$R^*$是$P$的阈值速率,如果速率为$R^* + ε$的随机码极有可能满足$P$,而速率为$R^* - ε$的随机码极不可能满足$P$。尽管随机码在编码理论中已被广泛研究,但即便是上述这类相对简单的性质,其阈值速率也尚未得到充分理解。\n 我们刻画了一大类性质的阈值速率。这些性质与上述例子类似,通过包含特定的码字集合来定义,且这些码字集合具有适当的“对称性”。对于该类中的性质,我们证明其阈值速率实际上等于简单一阶矩计算得到的下界。我们的技术不仅确定了上述性质$P$的阈值速率,还给出了若干参数 regimes 下列恢复(list-recovery)阈值速率的紧界,以及一种用于估计一般下列恢复阈值速率的高效算法。

英文摘要:

Suppose that $P$ is a property that may be satisfied by a random code $C \subset Σ^n$. For example, for some $p \in (0,1)$, ${P}$ might be the property that there exist three elements of $C$ that lie in some Hamming ball of radius $pn$. We say that $R^*$ is the threshold rate for ${P}$ if a random code of rate $R^* + ε$ is very likely to satisfy ${P}$, while a random code of rate $R^* - ε$ is very unlikely to satisfy ${P}$. While random codes are well-studied in coding theory, even the threshold rates for relatively simple properties like the one above are not well understood. We characterize threshold rates for a rich class of properties. These properties, like the example above, are defined by the inclusion of specific sets of codewords which are also suitably "symmetric". For properties in this class, we show that the threshold rate is in fact equal to the lower bound that a simple first-moment calculation obtains. Our techniques not only pin down the threshold rate for the property ${P}$ above, they give sharp bounds on the threshold rate for list-recovery in several parameter regimes, as well as an efficient algorithm for estimating the threshold rates for list-recovery in general.

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