# News for September 2017

Summer came and went, and Fall begins at full throttle with a (metric) ton of papers. Eight that we counted — if any was missed, please mention it in the comments!

Efficient Removal without Efficient Regularity, by Lior Gishboliner, Asaf Shapira (arXiv). Obtaining efficient removal lemmata for graphs pattern (such as triangle, to name the most famous), that is removal results with bounds on the number of copies of the pattern that is not mind-blowingly huge like a tower of $$\varepsilon$$, is a classic and longstanding problem. This work makes significant progress for the last remaining case, i.e. for the pattern $$C_4$$: providing bounds that are merely exponential in $$\varepsilon$$.

Local decoding and testing of polynomials over grids, by Srikanth Srinivasan, Madhu Sudan (arXiv, ECCC). In this work, the authors study the local decodability and local testability of error-correcting codes corresponding to low-degree polynomials on the grid $$\{0,1\}^n$$ (over a field $$\mathbb{F}\supseteq \{0,1\}$$). Obtaining both positive and negative results on these, a consequence of their results is a separation between local testability and local decodability for a natural family of codes.

Lower Bounds for Approximating Graph Parameters via Communication Complexity, by Talya Eden and Will Rosenbaum (arXiv). This paper establishes an analogue of the framework of Blais, Brody, and Matulef (2012), which enabled one to obtain property testing lower bounds by a reduction from communication complexity, for the setting of graph parameter estimation. The authors then leverage this technique to give new and simpler proofs of lower bounds for several such estimation tasks.

A Note on Property Testing Sum of Squares and Multivariate Polynomial Interpolation, by Aaron Potechin and Liu Yang (arXiv). The authors introduce and study the question of testing “sum-of-square-ness,” i.e. the property of a degree-$$d$$-polynomial being a sum of squares. Specifically, they show that one-sided sample-based testers cannot do much better than the trivial approach, that is that they require sample complexity $$n^{\Omega(d)}$$ — while learning the polynomial can be done with $$n^{O(d)}$$ samples.

Sharp Bounds for Generalized Uniformity Testing, by Ilias Diakonikolas, Daniel Kane, and Alistair Stewart (arXiv, ECCC). Remember the post from last month, which included a paper on “Generalized Uniformity Testing”? Well, this paper more or less settles the question, establishing tight bounds on the sample complexity of testing whether an (unknown) probability distribution over an (unknown) discrete domain is uniform on its support, or far from every uniform distribution. Specifically, the authors significantly strengthen the previous upper bound, by getting the right dependence on $$\varepsilon$$ for all regimes; and complement it by a matching worst-case lower bound.

Sample-Optimal Identity Testing with High Probability, by Ilias Diakonikolas, Themis Gouleakis, John Peebles, and Eric Price  (ECCC). Usually, in property testing we do not care too much about the error probability $$\delta$$: if one can achieve $$1/3$$, then simple repetition can bring it down to $$\delta$$ at the mild price of a $$\log(1/\delta)$$ factor in the query/sample complexity. Is that necessary, though? This paper shows that for uniformity and identity testing of distributions, the answer is “no”: for some regimes, this repetition trick is strictly suboptimal, as one can pay instead only a multiplicative $$\sqrt{\log(1/\delta)}$$. And quite interestingly, this improvement is achieved with the simplest algorithm one can think of: by considering the empirical distribution obtained from the samples.

A Family of Dictatorship Tests with Perfect Completeness for 2-to-2 Label Cover, by Joshua Brakensiek and Venkatesan Guruswami (ECCC). While I tried to paraphrase the original abstract, but my attempts only succeeded in making it less clear; and, for fear of botching the job, decided to instead quote said abstract: “[the authors] give a family of dictatorship tests with perfect completeness [that is, one-sided] and low-soundness for 2-to-2 constraints. The associated 2-to-2 conjecture has been the basis of some previous inapproximability results with perfect completeness. However, evidence towards the conjecture in the form of integrality gaps even against weak semidefinite programs has been elusive. [Their] result provides some indication of the expressiveness and non-triviality of 2-to-2 constraints, given the close connections between dictatorship tests and satisfiability and approximability of CSPs.”

A polynomial bound for the arithmetic $$k$$-cycle removal lemma in vector spaces, by Jacob Fox, László Miklós Lovász, and Lisa Sauermann (arXiv). And back to removal lemmata! This work proves a generalization of Green’s arithmetic $$k$$-cycle removal lemma, which held for any $$k\geq 3$$ and abelian group $$G$$; however, the bounds in this lemma were quite large — i.e., tower-ype. Here, the authors establish an efficient lemma (with polynomial bounds) for the case of the group $$\mathbb{F}_p^n$$ (where $$p\geq 2$$ is any fixed prime, and $$k\geq 3$$).

Update (10/04): Finally, a paper we covered last summerThe Dictionary Testing Problem, by Siddharth Barman, Arnab Bhattacharyya, and Suprovat Ghoshal, went under signficant changes. Now titled Testing Sparsity over Known and Unknown Bases, it now includes (in addition to the previous results) a testing algorithm for sparsity with regard to a specific basis: given a matrix $$A \in \mathbb{R}^{d \times m}$$ and unknown input vector $$y \in \mathbb{R}^d$$, does $$y$$ equal $$Ax$$ for some $$k$$-sparse vector $$x$$, or is it far from all such representations?

Update (10/5): we missed a recent paper of Benjamin Fish, Lev Reyzin, and Benjamin Rubinstein on Sublinear-Time Adaptive Data Analysis (arXiv). While not directly falling into the umbrella of property testing, this work considers sublinear-time algorithms for adaptive data analysis — similar in goal and spirit to property testing.