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arXiv 1507.05136cs.DScs.CC
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四次SOS计划中种植团的紧下界

Tight Lower Bounds for Planted Clique in the Degree-4 SOS Program

Prasad Raghavendra, Tselil Schramm

摘要:

我们给出了种植集团问题的4阶平方和SDP松弛的$\tildeΩ(\sqrt{n})$的下界。具体来说,我们表明,在一个Erdös-Rényi图$G(n,\tfrac{1}{2})$,有很高的概率有一个可行的点的度-4 SOS放松的集团问题的目标值$\tildeΩ(\sqrt{n})$,使程序无法区分随机图和随机图与种植集团的大小$\tilde{O}(\sqrt{n})$。这个界限很紧.我们以Deshpande、Montanari和Meka等人的作品为基础,分别给出了$\tildeΩ(n^{1/3})$和$\tildeΩ(n^{1/4})$的下界。我们通过对他们工作中提出的SDP解决方案进行扰动来改进他们的结果,然后表明这种扰动仍然是PSD,因为目标值接近$\tildeΩ(n^{1/2})$。在一项独立的工作中,Hopkins、Kothari和Potechin [HKP 15]获得了$4$ SOS松弛度的类似下限。

英文摘要:

We give a lower bound of $\tildeΩ(\sqrt{n})$ for the degree-4 Sum-of-Squares SDP relaxation for the planted clique problem. Specifically, we show that on an Erdös-Rényi graph $G(n,\tfrac{1}{2})$, with high probability there is a feasible point for the degree-4 SOS relaxation of the clique problem with an objective value of $\tildeΩ(\sqrt{n})$, so that the program cannot distinguish between a random graph and a random graph with a planted clique of size $\tilde{O}(\sqrt{n})$. This bound is tight. We build on the works of Deshpande and Montanari and Meka et al., who give lower bounds of $\tildeΩ(n^{1/3})$ and $\tildeΩ(n^{1/4})$ respectively. We improve on their results by making a perturbation to the SDP solution proposed in their work, then showing that this perturbation remains PSD as the objective value approaches $\tildeΩ(n^{1/2})$. In an independent work, Hopkins, Kothari and Potechin [HKP15] have obtained a similar lower bound for the degree-$4$ SOS relaxation.

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