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arXiv 1609.06355cs.CCmath.COmath.PR
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非法分布和局部可解码码

Outlaw distributions and locally decodable codes

Jop Briët, Zeev Dvir, Sivakanth Gopi

摘要:

局部可解码码(LDC)是允许使用对损坏的编码的少量查询来解码单个消息位的纠错码。尽管几十年的研究,查询复杂度和码字长度之间的最佳权衡是远远没有理解。在这项工作中,我们给出了一个新的特征的最不发达国家使用分布的布尔函数的期望是很难近似(在~ $L_\infty$ ~范数)与少量的样本。我们为这样的分布创造了“非法分布”这个术语,因为它们“无视”大数定律。我们表明,不法分布的存在,充分“光滑”的功能意味着存在的恒定查询最不发达国家,反之亦然。我们从有限域关联几何、加法组合数学和超图(非)展开子等方面给出了光滑函数上非法分布的几种候选形式。我们还证明了一个有用的引理表明,(光滑)最不发达国家只需要平均工作在一个随机消息和随机消息索引可以变成真正的最不发达国家的成本只有常数因子的参数。

英文摘要:

Locally decodable codes (LDCs) are error correcting codes that allow for decoding of a single message bit using a small number of queries to a corrupted encoding. Despite decades of study, the optimal trade-off between query complexity and codeword length is far from understood. In this work, we give a new characterization of LDCs using distributions over Boolean functions whose expectation is hard to approximate (in~$L_\infty$~norm) with a small number of samples. We coin the term `outlaw distributions' for such distributions since they `defy' the Law of Large Numbers. We show that the existence of outlaw distributions over sufficiently `smooth' functions implies the existence of constant query LDCs and vice versa. We give several candidates for outlaw distributions over smooth functions coming from finite field incidence geometry, additive combinatorics and from hypergraph (non)expanders. We also prove a useful lemma showing that (smooth) LDCs which are only required to work on average over a random message and a random message index can be turned into true LDCs at the cost of only constant factors in the parameters.

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