从Sylvester-Gallai检验到秩界:改进的深度3电路黑盒恒等式检验
From Sylvester-Gallai Configurations to Rank Bounds: Improved Black-box Identity Test for Depth-3 Circuits
摘要:
本文研究了k阶和d阶的深度3电路的恒等式测试问题。我们给出了这类恒等式的一个新的结构定理。我们的定理的直接应用改进了已知的有理数上的确定性d^{k^k}-时间黑盒恒等式测试(Kayal-Saraf,FOCS 2009),使其需要d^{k^2}-时间。我们的结构定理本质上说,在一个真正的深度3单位的独立变量的数量是非常小的。这个定理肯定地解决了Dvir-Shpilka(STOC 2005)和Kayal-Saraf(FOCS 2009)提出的更强的秩问题。我们的技术提供了一个统一的框架,实际上击败了所有已知的排名界限,因此为黑盒身份测试提供了最佳的运行时间(对于每个字段)。我们的主要定理(几乎最优)钉在一个非常透明的方式高维西尔维斯特-Gallai定理和深度3身份证的秩之间的关系。Dvir-Shpilka(STOC 2005)暗示了这一点的存在,但Kayal-Saraf(FOCS 2009)首先证明了这一点。我们引入了Sylvester-Gallai秩界的概念,并证明了这与深度3恒等秩界之间的密切联系。我们还证明了第一个定理高维Sylvester-Gallai配置在任何领域。我们的证明和技术是非常不同的,从以前的结果和设计一个非常有趣的组合数学和代数系综。后者的概念是理想的理论和涉及一个新的中国剩余定理。我们的证明方法解释了任何深度为3的身份C的结构:有一个核的C,形成一个低秩的身份,而其余的是一个高维Sylvester-Gallai配置。
英文摘要:
We study the problem of identity testing for depth-3 circuits of top fanin k and degree d. We give a new structure theorem for such identities. A direct application of our theorem improves the known deterministic d^{k^k}-time black-box identity test over rationals (Kayal-Saraf, FOCS 2009) to one that takes d^{k^2}-time. Our structure theorem essentially says that the number of independent variables in a real depth-3 identity is very small. This theorem settles affirmatively the stronger rank conjectures posed by Dvir-Shpilka (STOC 2005) and Kayal-Saraf (FOCS 2009). Our techniques provide a unified framework that actually beats all known rank bounds and hence gives the best running time (for every field) for black-box identity tests. Our main theorem (almost optimally) pins down the relation between higher dimensional Sylvester-Gallai theorems and the rank of depth-3 identities in a very transparent manner. The existence of this was hinted at by Dvir-Shpilka (STOC 2005), but first proven, for reals, by Kayal-Saraf (FOCS 2009). We introduce the concept of Sylvester-Gallai rank bounds for any field, and show the intimate connection between this and depth-3 identity rank bounds. We also prove the first ever theorem about high dimensional Sylvester-Gallai configurations over any field. Our proofs and techniques are very different from previous results and devise a very interesting ensemble of combinatorics and algebra. The latter concepts are ideal theoretic and involve a new Chinese remainder theorem. Our proof methods explain the structure of any depth-3 identity C: there is a nucleus of C that forms a low rank identity, while the remainder is a high dimensional Sylvester-Gallai configuration.
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