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arXiv 2008.07188cs.ITmath.IT
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通信复杂性的一个近优直和定理

A near-optimal direct-sum theorem for communication complexity

Rahul Jain

摘要:

我们证明了两方随机通信复杂性的一个近似最优直和定理。设$f\subseteq X \times Y\times Z$为关系,$\varepsilon> 0$和$k$为整数。我们证明了$$\mathrm{R}^{\mathrm{pub}}_\varepsilon(f^k) \cdot \log(\mathrm{R}^{\mathrm{pub}}_\varepsilon(f^k)) \ge Ω(k \cdot \mathrm{R}^{\mathrm{pub}}_\varepsilon(f)) \enspace,$$,其中$f^k= f \times \ldots \times f$($k$ -times)和$\mathrm{R}^{\mathrm{pub}}_\varepsilon(\cdot)$表示具有最坏情况错误$\varepsilon$的公共硬币随机通信复杂性。给出了一个具有通信代价$c \cdot k$和最坏错误$\varepsilon$的$f^k$的协议$\mathcal{P}$,给出了一个具有外部信息代价$O(c)$和最坏错误$\varepsilon$的$f$的协议$\mathcal{Q}$.然后,我们使用Barak,Braverman,Chen和Rao [2013]的消息压缩协议来模拟具有通信$O(c \cdot \log(c\cdot k))$的$\mathcal{Q}$,以得出我们的结果。为了显示这种减少,我们展示了一些新的链规则的能力,最大的信息,可以通过通信信道传输。我们使用博弈论中纳什均衡的强大概念,以及它在适当定义的博弈中的存在性,来得出容量的链式规则。这些链式规则是独立的利益。

英文摘要:

We show a near optimal direct-sum theorem for the two-party randomized communication complexity. Let $f\subseteq X \times Y\times Z$ be a relation, $\varepsilon> 0$ and $k$ be an integer. We show, $$\mathrm{R}^{\mathrm{pub}}_\varepsilon(f^k) \cdot \log(\mathrm{R}^{\mathrm{pub}}_\varepsilon(f^k)) \ge Ω(k \cdot \mathrm{R}^{\mathrm{pub}}_\varepsilon(f)) \enspace,$$ where $f^k= f \times \ldots \times f$ ($k$-times) and $\mathrm{R}^{\mathrm{pub}}_\varepsilon(\cdot)$ represents the public-coin randomized communication complexity with worst-case error $\varepsilon$. Given a protocol $\mathcal{P}$ for $f^k$ with communication cost $c \cdot k$ and worst-case error $\varepsilon$, we exhibit a protocol $\mathcal{Q}$ for $f$ with external-information-cost $O(c)$ and worst-error $\varepsilon$. We then use a message compression protocol due to Barak, Braverman, Chen and Rao [2013] for simulating $\mathcal{Q}$ with communication $O(c \cdot \log(c\cdot k))$ to arrive at our result. To show this reduction we show some new chain-rules for capacity, the maximum information that can be transmitted by a communication channel. We use the powerful concept of Nash-Equilibrium in game-theory, and its existence in suitably defined games, to arrive at the chain-rules for capacity. These chain-rules are of independent interest.

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