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arXiv 2008.00266cs.CC
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关于Fourier稀疏布尔函数的奇偶决策树

On parity decision trees for Fourier-sparse Boolean functions

Nikhil S. Mande, Swagato Sanyal

摘要:

我们研究布尔函数的奇偶决策树。我们研究的动机是异或函数的对数秩猜想及其与傅立叶分析和奇偶决策树复杂性的联系。设f是一个布尔函数,具有Fourier支撑S和Fourier稀疏度k. 1)我们证明了通过概率的方法,存在一个奇偶性决策树的深度为O(sqrt k),计算f。这与布尔函数的奇偶性决策树复杂度的最佳已知上限相匹配(Tsang,Wong,Xie,and Zhang,FOCS 2013)。此外,虽然先前的构造(Tsang等人,FOCS 2013,Shpilka,Tal和Volk,Comput.复杂. 2017)通过仔细选择在每一步中要查询的奇偶校验来构建树,我们的证明表明,奇偶校验的简单抽样就足够了。2)我们推广上述结果表明,如果布尔函数的傅立叶谱满足一个自然的“折叠属性”,那么上述证明可以适用于建立存在的树的复杂性多项式小于O(sqrt k)。在这方面,我们做出一个猜想,如果该猜想为真,则意味着XOR函数的通信复杂性由其通信矩阵的秩的四次方根限制,从而改进了先前已知的秩的平方根的上限(Tsang等人,FOCS 2013,Lovett,J. ACM. 2016年)。3)可以用初等技巧证明,对于任何布尔函数f和S中的所有奇偶对(alpha,beta),存在S中的另一对奇偶对(gamma,delta),使得alpha + beta = gamma + delta。我们证明了在F_2 ^n中一定存在多个gamma,使得在S中至少存在三对(alpha_1,alpha_2)宇称,其中alpha_1 + alpha_2 = gamma.

英文摘要:

We study parity decision trees for Boolean functions. The motivation of our study is the log-rank conjecture for XOR functions and its connection to Fourier analysis and parity decision tree complexity. Let f be a Boolean function with Fourier support S and Fourier sparsity k. 1) We prove via the probabilistic method that there exists a parity decision tree of depth O(sqrt k) that computes f. This matches the best known upper bound on the parity decision tree complexity of Boolean functions (Tsang, Wong, Xie, and Zhang, FOCS 2013). Moreover, while previous constructions (Tsang et al., FOCS 2013, Shpilka, Tal, and Volk, Comput. Complex. 2017) build the trees by carefully choosing the parities to be queried in each step, our proof shows that a naive sampling of the parities suffices. 2) We generalize the above result by showing that if the Fourier spectra of Boolean functions satisfy a natural "folding property", then the above proof can be adapted to establish existence of a tree of complexity polynomially smaller than O(sqrt k). We make a conjecture in this regard which, if true, implies that the communication complexity of an XOR function is bounded above by the fourth root of the rank of its communication matrix, improving upon the previously known upper bound of square root of rank (Tsang et al., FOCS 2013, Lovett, J. ACM. 2016). 3) It can be shown by elementary techniques that for any Boolean function f and all pairs (alpha, beta) of parities in S, there exists another pair (gamma, delta) of parities in S such that alpha + beta = gamma + delta. We show, among other results, that there must exist several gamma in F_2^n such that there are at least three pairs (alpha_1, alpha_2) of parities in S with alpha_1 + alpha_2 = gamma.

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