News for September 2021

A nice array of papers for this month, ranging from distribution testing, dense graph property testing, sublinear graph algorithms, and various mixtures of them. Let us now sample our spread! (Adding another semistreaming paper who achieved similar results to another posted paper. -Ed)

A Lower Bound on the Complexity of Testing Grained Distributions by Oded Goldreich and Dana Ron (ECCC). A discrete distribution is called \(m\)-grained if all probabilities are integer multiples of \(1/m\). This paper studies the complexity of testing this property of distributions. For simplicity, consider the property of being \(n/2\)-grained, where the support size is \(n\). The classic lower bound for testing uniformity shows that \(\Omega(\sqrt{n})\) samples are required to distinguish the uniform distribution from a distribution uniform on \(n/2\) elements. Thus, we get a lower bound of \(\Omega(\sqrt{n})\) for testing \(n/2\)-grainedness (if I am permitted to use that word). This paper proves a lower bound of \(\Omega(n^c)\), for all constant \(c < 1\). It is conjectured that the lower bound is actually \(\Omega(n/\log n)\), which would match the upper bound (for any label-invariant property).

Testing Distributions of Huge Objects by Oded Goldreich and Dana Ron (ECCC). This paper introduced a new model that marries distribution testing with property testing on strings. The “object” of interest is a distribution \(\mathcal{D}\) over strings of length \(n\). We wish to test if \(\mathcal{D}\) possesses some property. The tester can get a random string \(x\) from the distribution, and can query any desired index of \(x\). The distance between distributions is defined using the earthmover distance (where we use the Hamming distance between strings). This model is called the DoHO (Distributions of Huge Objects) model. There are many questions posed and connections drawn to classical property testing and distribution testing. What I find interesting is a compelling application: the distribution \(\mathcal{D}\) may represent noisy or perturbed versions of a single object. The DoHO model gives a natural generalization of standard property testing to noisy objects. This paper considers problems such as testing if \(\mathcal{D}\) is: a random perturbation of a string, or a random cyclic shift, or a random isomorphism of a graph.

Sublinear Time and Space Algorithms for Correlation Clustering via Sparse-Dense Decompositions by Sepehr Assadi and Chen Wang (arXiv). Correlation clustering is a classic problem where edges in a graph are labeled ‘+’ or ‘-‘, denoting whether these edges should be uncut or cut. The aim is to cluster the graph minimizing the total “disagreements” (cut ‘+’ edges or uncut ‘-‘ edges). This paper gives an \(O(1)\)-approximation algorithm that runs in \(O(n\log^2n)\) time; this is the first sublinear time approximation algorithm for this problem. Correlation clustering has seen results for the property testing/sublinear algorithms community, first by Bonchi, Garcia Soriano, and Kutzkov. But previous results were essentially on the dense graph model, giving \(O(\epsilon n^2)\) error assuming adjacency matrix input. This paper considers access to the adjacency list of ‘+’ edges. Interestingly (from a technical standpoint), the key tool is a new sparse-dense decomposition. Such decompositions emerged from the seminal work of Assadi-Chen-Khanna for sublinear \((\Delta+1)\)-colorings, and it is great to see applications beyond coloring.

Sublinear-Time Computation in the Presence of Online Erasures by Iden Kalemaj, Sofya Raskhodnikova, and Nithin Varma (arXiv). Can property testing be done when portions of the input are hidden? This question was first raised by Dixit-Raskhodnikova-Thakurta-Varma, who gave a model of erasure-resilient testing. There is an adversary who hides (erases) part of the input function; queries to those parts just yield a dummy symbol. This paper defines an online version of this model. There is an erasure parameter \(t\). On each query by the property tester, the adversary can erase \(t\) values of the function. Consider the property of classic linearity of functions \(f:\{0,1\}^d \rightarrow \{0,1\}\). The BLR tester queries triples of pairs \((x,y, x \oplus y)\). Observe how this tester is easily defeated by our adversary, by erasing the value \(f(x\oplus y)\). One of the main results of this paper is a \(O(1/\varepsilon)\)-query tester for linearity, that works for any constant erasure parameter \(t\). Note that this matches the bound for the standard setting. There are a number of results for other classic properties, such as monotonicity (sortedness) and Lipschitz.

Sublinear Time Eigenvalue Approximation via Random Sampling by Rajarshi Bhattacharjee, Cameron Musco, and Archan Ray (arXiv). Consider the problem of estimating all the eigenvalues of a real, symmetric \(n \times n\) matrix \(M\) with bounded entries, in sublinear time. The main result shows that the eigenvalues of a uniform random \(O(\epsilon^{-4}\log n)\) principal submatrix can be used to approximate all eigenvalues of \(M\) up to additive error \(\epsilon n\). One can think of this as a sort of concentration inequality for eigenvalues. This result follows (and builds upon) work of Bakshi-Chepurko-Jayaram on property testing semidefiniteness. The key idea is that eigenvectors corresponding to large eigenvalues have small infinity norm: intuitively, since all entries in \(M\) are bounded, such an eigenvector must have its mass spread out among many coordinates. Hence, we can get information about it by randomly sampling a few coordinates. The paper also shows that approach of taking principal submatrices requires taking \(\Omega(\epsilon^{-2})\) columns/rows.

Deterministic Graph Coloring in the Streaming Model by Sepehr Assadi, Andrew Chen, and Glenn Sun (arXiv). This is technically not a sublinear algorithms paper (well ok, streaming is sublinear, but we tend not to cover the streaming literature. Maybe we should? – Ed.) But, I think that the connections are of interest to our community of readers. The main tool of sublinear \((\Delta+1)\)-coloring algorithm of Assadi-Chen-Khanna is the palette sparsification lemma (\(\Delta\) is the maximum degree). This lemma shows that vertices can randomly shorten their ”palette” of colors, after which all colorings from these palettes lead to very few monochromatic edges. This is an immensely powerful tool, since one can get immediately sublinear complexity algorithms in many models: adjacency list, streaming, distributed. Is the randomness necessary? Note that these algorithms run in \(\Omega(n)\) time/space, so it is conceivable that deterministic sublinear algorithms exists. This paper shows that randomization is necessary in the semi-streaming model (space \(O(n poly(\log n))\)). Indeed, there exist no deterministic semi-streaming algorithms that can achieve even \(\exp(\Delta^{o(1)})\) colorings.

Adversarially Robust Coloring for Graph Stream by Amit Chakrabarti, Prantar Ghosh, and Manuel Stoeckl (arXiv). This paper studies the same problem as the above, but presents the results in a different way. In a randomized algorithm, we normally think of an adversary that fixes a (hard) input, and the algorithm then makes its random decisions. An adaptive adversary is one that changes the input (stream) based on the decisions of an algorithm. In this definition, a robust algorithm is one that can give correct answers, even for adversarially generated output. A deterministic algorithm is automatically robust. This paper show that there do not exist semi-streaming algorithms that can achieve \((\Delta+1)\)-colorings. The quantitative lower bound is weaker (\(\Omega(\Delta^2)\) colors), but it is against a stronger adversary.

News for August 2021

This month saw four papers. One on group testing, another on distribution testing, yet another which makes progress on testing problems on decision trees and the last one on graph property testing. Without further ado, let’s dive in.

Group Testing with Non-identical Infection Probabilities by Mustafa Doger, Sennur Ulukus (arXiv) Consider the classic group testing problem. Here the setup is the following. You are given a bunch of individuals from a population \(\mathcal{P}\). You have an infection vector which records the infection status of each individual in the population where the \(i\)-th individual is infected with probability \(p_i\). You want to recover all the infected individuals. You are allowed to group individuals together and you can test the entire group in a single shot. If the group tests negative, you are happy all the tested individuals are off the hook. Otherwise, if the group tests positive, you need more tests for further classification. This paper proposes a greedy way to build pools of individuals you would test. The pools are built adaptively: as in future pools are built using the knowledge of how the preceding tests fared. The key result in the paper upperbounds the number of tests performed in terms of the entropy of the infection vector.

Uniformity Testing in the Shuffle Model: Simpler, Better, Faster by Clément L. Canonne, Hongyi Lyu (arXiv) Differentially private distribution testing as a research area has been gathering momentum steadily over the last few years. If you read our last month’s post, you might recall there are a wide variety of models of DP each corresponding to a different “threat model”. The most stringent among the most explored models is the “local model”, the least stringent being the “central model” and there is an intermediate threat model, the so called “shuffle model“. This paper simplifies the analysis of uniformity testing algorithm under the shuffle model and presents an algorithm with sample complexity \(O(k^{3/4})\) for testing uniformity over a support of size \([k]\).

On Learning and Testing Decision Tree by Nader H. Bshouty, Catherine A. Haddad-Zaknoon (arXiv) In our December 2020 post, we covered a result of Blanc et al., which proves the following: Suppose you are given a boolean function \(f\) and the property \(\mathcal{P}\) of size-\(s\) decision trees. The result of Blanc et al gives you a function \(g \in \mathcal{P}\) with \(dist(f,g) = O(dist (f, \mathcal{P}))\) where \(g \in \) is guaranteed to have decision tree complexity \(s^{O(\log^2 s)}\). This result implies a bi-criteria tester for the following property: is \(f \in \mathcal{P}\) or is \(f\) \(\varepsilon\)-far from having decision tree complexity \(\phi(s) = s^{O(\log^3 s)}\). The current paper improves this result by presenting a property tester with \(\phi(s) = s^{O(\log^2 s)}\).

The complexity of testing all properties of planar graphs, and the role of isomorphism by Sabyasachi Basu, Akash Kumar, C. Seshadhri (arXiv) (Disclaimer: I am one of the authors of this paper). This paper presents a result that I, in my biased opinion, find interesting. So, here is the setup. You are given a bounded degree planar graph. And I cook up some God-forsaken property and ask you to test it. Turns out, no matter how devilishly I cooked up the property, you can test in with \(\exp(O(\varepsilon^{-2}))\) queries. The nice happenstance is that you also have a matching lower bound of \(\exp(\Omega(\varepsilon^{-2}))\) queries! And interestingly, this lower bound is witnessed by the very natural property of testing isomorphism to a fixed graph which means that isomorphism is the hardest property of planar graphs.

Workshop on Algorithms for Large Data: We found WALD(O), and so can you!

Ainesh Bakshi, Rajesh Jayaram, and Samson Zhou are organizing a 3-day Workshop on Algorithms for Large Data (nicely abbreviated as WALD(O), the O standing for Online), featuring many talks which should be of interest to the readers of this blog, as well as an open problems and a poster sessions, and a junior/senior lunch. As the organizers describe it:

This workshop aims to foster collaborations between researchers across multiple disciplines through a set of central questions and techniques for algorithm design for large data. We will focus on topics such as sublinear algorithms, randomized numerical linear algebra, streaming and sketching, and learning and testing.

The workshop will take place on August 23 — August 25 (ET). Attendance is free, but registration is required by August 20th. More details at https://waldo2021.github.io/

New for July 2021

This month saw three papers appear online, together covering a rather broad range of topics: testing of regular languages, distribution testing under differential privacy, and local testability from high-dimensional expanders. Let’s dive in!

Property Testing of Regular Languages with Applications to Streaming Property Testing of Visibly Pushdown Languages, by Gabriel Bathie and Tatiana Starikovskaya (paper). Let \(L\in \Sigma^\ast\) be a regular language recognized by an automation with \(m\) states and \(k\) connected components: given as input a word \(u\in \Sigma^n\), what is the query complexity to test membership to \(L\) in Hamming distance? Edit distance? Or, more generally, weighted edit distance, where each letter of the word \(u\) comes with a weight? In this paper, the authors focus on non-adaptive, one-sided errors testing algorithms, for which they show an upper bound of \(q=O(k m \log(m/\varepsilon)/\varepsilon)\) queries (with running time \(O(m^2 q)\)), which they complement by a query complexity lower bound of \(\Omega(\log(1/\varepsilon)/\epsilon)\), thus matching the upper bound for languages recognized by constant-size automata. The guarantee for the upper bound is with respected to weighted edit distance, and thus implies the same upper bound for testing with respect to Hamming distance.
To conclude, the authors use an existing connection to streaming property testing to obtain new algorithms for property testing of visibly pushdown languages (VPL) in the streaming model, along with a new lower bound in that model.

High dimensional expansion implies amplified local testability, by Tali Kaufman and Izhar Oppenheim (arXiv). This paper sets out to show that codes that arise from high-dimensional expanders are locally testable (membership to the code can be tested using very few queries). To do so, the authors define a new notion of high-dimensional expanding system (HDE system), as well as that of amplified local testability, a stronger notion than local testability; they then prove that a code based on a HDE system satisfies this stronger notion. Moreover, they show that many well-known families of codes are, in fact, HDE system codes, and therefore satisfy this stronger notion of local testability as well.

Finally, a survey on differential privacy, with a foray into distribution testing:

Differential Privacy in the Shuffle Model: A Survey of Separations, by Albert Cheu (arXiv). If you are familiar with differential privacy (DP), you may recall that there are several notions of DP, each meant to address a different “threat model” (depending on whom you trust with your data). Shuffle DP is one of them, intermediate between “central” DP and the more stringent “local” DP. Long story short: with shuffle DP, the tradeoff between privacy and accuracy can be strictly in-between what’s achievable in central and local DP, and that’s the case for one of the usual suspects of distribution testing, uniformity testing (“I want to test if the data uniformly distributed, but now, with privacy of that data in mind”). The survey discusses what is known about this in Sections 3.3 and 6, and what the implications are; but there are quite a few questions left unanswered… Long story short: a very good introduction to shuffle privacy, and to open problems in that area!

News for June 2021

A quieter month after last month’s bonanza. One (applied!) paper on distribution testing, a paper on tolerant distribution testing, and a compendium of open problems. (Ed: alas, I missed the paper on tolerant distribution testing, authored by one of our editors. Sorry, Clément!)

Learning-based Support Estimation in Sublinear Time by Talya Eden, Piotr Indyk, Shyam Narayanan, Ronitt Rubinfeld, Sandeep Silwal, and Tal Wagner (arXiv). A classic problem in distribution testing is that of estimating the support size \(n\) of an unknown distribution \(\mathcal{D}\). (Assume that all elements in the support have probability at least \(1/n\).) A fundamental result of Valiant-Valiant (2011) proves that the sample complexity of this problem is \(\Theta(n/\log n)\). A line of work has emerged in trying to reduce this complexity, with additional sources of information. Canonne-Rubinfeld (2014) showed that, if one can query the exact probabilities of elements, then the complexity can be made independent of \(n\). This paper studies a robust version of this assumption: suppose, we can get constant factor approximations to the probabilities. Then, the main result is that we can get a query complexity of \(n^{1-1/\log(\varepsilon^{-1})} \ll n/\log n\) (where the constant \(\varepsilon\) denotes the additive approximation to the support size). This paper also does empirical experiments to show that the new algorithm is indeed better in practice. Moreover, it shows that existing methods degraded rapidly with poorer probability estimates, while the new algorithm maintains its accuracy even with such estimates.

The Price of Tolerance in Distribution Testing by Clément L. Canonne, Ayush Jain, Gautam Kamath, and Jerry Li (arXiv). While we have seen many results in distribution testing, the subject of tolerance is one that hasn’t received as much attention. Consider the problem of testing if unknown distribution \(\mathcal{p}\) (over domain \([n]\)) is the same as known distribution \(\mathcal{q}\). We wish to distinguish \(\varepsilon_1\)-close from \(\varepsilon_2\)-far, under total variation distance. When \(\varepsilon_1\) is zero, this is the standard property testing setting, and classic results yield \(\Theta(\sqrt{n})\) sample complexity. If \(\varepsilon_1 = \varepsilon_2/2\), then we are looking for a constant factor approximation to the distance. And the complexity is \(\Theta(n/\log n)\). Surprisingly, nothing was known in better. Until this paper, that is. The main result gives a complete characterization of sample complexity (up to log factors), for all values of \(\varepsilon_1, \varepsilon_2\). Remarkably, the sample complexity has an additive term \((n/\log n) \cdot (\varepsilon_1/\varepsilon^2_2)\). Thus, when \(\varepsilon_1 > \sqrt{\varepsilon_2}\), the sample complexity is \(\Theta(n/\log n)\). When \(\varepsilon_1\) is smaller, the main result gives a smooth dependence on the sample complexity. One the main challenges is that existing results use two very different techniques for the property testing vs constant-factor approximation regimes. The former uses simpler \(\ell_2\)-statistics (e.g. collision counting), while the latter is based on polynomial approximations (estimating moments). The upper bound in this paper shows that simpler statistics based on just the first two moments suffice to getting results for all regimes of \(\varepsilon_1, \varepsilon_2\).

Open Problems in Property Testing of Graphs by Oded Goldreich (ECCC). As the title clearly states, this is a survey covering a number of open problems in graph property testing. The broad division is based on the query model: dense graphs, bounded degree graphs, and general graphs. A reader will see statements of various classic open problems, such as the complexity of testing triangle freeness for dense graphs and characterizing properties that can be tested in \(poly(\varepsilon^{-1})\) queries. Arguably, there are more open problems (and fewer results) for testing in bounded degree graphs, where we lack broad characterizations of testable properties. An important, though less famous (?), open problem is that of the complexity of testing isomorphism. It would appear that the setting of general graphs, where we know the least, may be the next frontier for graph property testing. A problem that really caught my eye: can we transform testers that work for bounded degree graphs into those that work for bounded arboricity graphs? The latter is a generalization of bounded degree that has appeared in a number of recent results on sublinear graph algorithms.

Looking back at WOLA’21: Videos available

The fifth Workshop on Local Algorithms (WOLA’21) took place earlier this month, and the recordings of the invited talks are now available on YouTube. If you missed the workshop, or want to refresh your memory, here are the recordings (ordered by the workshop schedule):

Thanks again to the speakers and organizers, and looking forward to WOLA’22!

News for May 2021

We hope you are all staying safe. With massive vaccination programs across the globe we hope you and your loved ones are getting back to what used to be normal. With that out of the way, let us circle back to Property Testing. This month was less sleepy as compared to the two preceding months and we saw six papers in total (two of them explore problems in quantum property testing). Without further ado, let us take a deeper dive.

GSF-locality is not sufficient for proximity-oblivious testing, by Isolde Adler, Noleen Kohler, Pan Peng (arXiv) The notion of proximity oblivious testers was made explicit in the seminal work of Goldreich and Ron in 2009 [GR09]. A proximity oblivious tester for a graph property is a constant query tester that rejects a graph with probability that monotonically increases with distance to the property. (Edit: Correction) A property is called proximity oblivious testable (or PO testable) if it has a one sided proximity oblivious tester. [GR09] gave a characterization of which properties \(\Pi\) are PO testable in the bounded degree model if and only if it is a “local” property of some kind which satisfies a certain non propagation condition. [GR09] conjectured that all such “local” properties satisfy this non propagation condition. This paper refutes the above conjecture from [GR09].

Coming up next. More action on triangle freeness.

Testing Triangle Freeness in the General Model in Graphs with Arboricity \(O(\sqrt n)\), by Reut Levi (arXiv) PTReview readers are likely to be aware that triangle freeness has been a rich source of problems for developing new sublinear time algorithms. This paper considers the classic problem of testing triangle freeness in general graphs. In the dense case, algorithms with running time depending only on \(\varepsilon\) are known thanks to the work of Alon, Fischer, Krivelevich and Szegedy. In the bounded degree case, Goldreich and Ron gave testers with query complexity \(O(1/\varepsilon)\). This paper explores the problem in general graph case and proves an upper bound of \(O(\Gamma/d_{avg} + \Gamma)\) where \(\Gamma\) is the arboricity of the graph. The author also shows that this upperbound is tight for graphs with arboricity at most \(O(\sqrt n)\). Curiously enough, the algorithm does not take arboricity of the graph as an input and yet \(\Gamma\) (the arboricity) shows up in the upper and lower bounds.

Testing Dynamic Environments: Back to Basics, by Yonatan Nakar and Dana Ron (arXiv) Goldreich and Ron introduced the problem of testing “dynamic environments” in 2014. Here is the setup for this problem. You are given an environment that evolves according to a local rule. Your goal is to query some of the states in the system at some point of time and determine if the system is evolving according to some fixed rule or is far from it. In this paper, the authors consider environments defined by elementary cellular automata which evolve according to threshold rules as one of the first steps towards understanding what makes a dynamic environment tested efficiently. The main result proves the following: if your local rules satisfy some conditions, you can use a meta algorithm with query complexity \(poly(1/\varepsilon)\) which is non adaptive and has one sided error. And all the threshold rules indeed satisfy these conditions which means they can be tested efficiently.

Identity testing under label mismatch, by Clement Canonne and Karl Wimmer (arXiv) This paper considers a classic problem distribution testing with the following twist. Let \(q\) denote a distribution supported on \([n]\). You are given access to samples from another distribution \(p\) where \(p = q \circ \pi\) where \(\pi\) is some unknown permutation. Thus, I relabel the data and I give you access to samples from the relabeled dataset. Under this promise, note that identity testing becomes a trivial problem if \(q\) is known to be uniform over \([n]\). The authors develop algorithms for testing and tolerant testing of distributions under this additional promise of \(p\) being a permutation of some known distribution \(q\). The main result shows as exponential gap between the sample complexity of testing and tolerant testing under this promise. In particular, identity testing under the promise of permutation has sample complexity \(\Theta(\log^2 n)\) whereas tolerant identity testing under this promise has sample complexity \(\Theta(n^{1-o(1)})\).

Testing symmetry on quantum computers, by Margarite L. LaBorde and Mark M. Wilde (arXiv) This paper develops algorithms which test symmetries of a quantum states and changes generated by quantum circuits. These tests additionally also quantify how symmetric these states (or channels) are. For testing what are called “Bose states” the paper presents efficient algorithms. The tests for other kinds of symmetry presented in the paper rely on some aid from a quantum prover.

Quantum proofs of proximity, by Marcel Dall’Agnol, Tom Gur, Subhayan Roy Moulik, Justin Thaler (ECCC) The sublinear time (quantum) computation model has been gathering momentum steadily over the past several years. This paper seeks to understand the power of \({\sf QMA}\) proofs of proximity for property testing (recall \({\sf QMA}\) is the quantum analogue of \({\sf NP}\)). On the algorithmic front, the paper develops sufficient conditions for properties to admit efficient \({\sf QMA}\) proofs of proximity. On the complexity front, the paper demonstrates a property which admits an efficient \({\sf QMA}\) proof but does not admit a \({\sf MA}\) or an interactive proof of proximity.

Announcing WOLA’21 (Workshop on Local Algorithms)

The fifth WOLA (Workshop on Local Algorithms) will be virtual, and take place June 14-15. Registration is free, but required: please fill this form by June 10th to attend.

Local algorithms — that is, algorithms that compute and make decisions on parts of the output considering only a portion of the input — have been studied in a number of areas in theoretical computer science and mathematics. Some of the related areas include sublinear-time algorithms, distributed algorithms, streaming algorithms, (massively) parallel algorithms, inference in large networks, and graphical models. These communities have similar goals but a variety of approaches, techniques, and methods. This workshop is aimed at fostering dialogue and cross-pollination of ideas between the various communities.

This year, the workshop will include:

  • A poster session: Please submit your poster proposal (title and abstract) at by May 26th. Everyone is invited to contribute. This session will take place on gather.town.
  • Invited long talks: the tentative schedule is available, and features talks by James Aspnes, Jelani Nelson, Elaine Shi, Christian Sohler, Uri Stemmer, and Mary Wootters.
  • Junior-Senior social meetings
  • An AMA (Ask Me Anything) session, moderated by Merav Parter
  • A Slack channel
  • An Open Problems session

The Program Committee of WOLA 2021 is comprised of:

  • Venkatesan Guruswami (CMU)
  • Elchanan Mossel (MIT)
  • Merav Parter (Weizmann Institute of Science)
  • Sofya Raskhodnikova (chair) (Boston University)
  • Gregory Valiant (Stanford)

and the organizing committee:

  • Sebastian Brandt (ETH)
  • Yannic Maus (Technion)
  • Slobodan Mitrović (MIT)

For more detail, see the website; to stay up to date with the latest announcements concerning WOLA, join our mailing list!

News for April 2021

A somewhat “sublinear” month of April, as far as property testing is concerned, with only one paper. (We may have missed some; if so, please let us know in the comments!)

Graph Streaming Lower Bounds for Parameter Estimation and Property Testing via a Streaming XOR Lemma, by Sepehr Assadi and Vishvajeet N (arXiv). This paper establishes space vs. pass trade-offs lower bounds for streaming algorithms, for a variety of graph tasks: that is, of the sort “any \(m\)-pass-streaming algorithm for task \(\mathcal{T}\) must use memory at least \(f(m)\).” The tasks considered include graph property estimation (size of the maximum matching, of the max cut, of the weight of the MST) and property testing for sparse graphs (connectivity, bipartiteness, and cycle-freeness). The authors obtained exponentially improved lower bounds for those, via reductions to a relatively standard problem, (noisy) gap cycle counting, for which they establish their main lower bound. As a key component of their proof, they prove a general direct product result (XOR lemma) for the streaming setting, showing that the advantage for solving the XOR of \(\ell\) copies of a streaming predicate \(f\) decreases exponentially with \(\ell\).

News for March 2021

A somewhat quieter month by recent standards. Three Two papers: graph property testing and quantum distribution testing. (Ed: The distribution testing paper was a revision of a paper we already covered in Sept 2020.)

Robust Self-Ordering versus Local Self-Ordering by Oded Goldreich (ECCC). In Nov 2020, we covered a paper that uses a tool called self-ordered graphs, that transferred bit string function lower bounds to graph property testing. Consider a labeled graph. A graph is self-ordered if its automorphism group only contains the identity element (it has no non-trivial isomorphisms). A graph is robustly self-ordered, if every permutation of the vertices leads to a (labeled) graph that is sufficiently “far” according to edit distance. Given a self-ordered graph \(G\), a local self-ordering procedure is the following. Given access to a copy \(G’\) of \(G\) and a vertex \(v \in V(G’)\), this procedure determines the (unique) vertex in \(V(G)\) that corresponds to \(v\) with sublinear queries to \(G\). In other words, it can locally “label” the graph. Intuitively, one would think that more robustly self-ordered graphs will be easier to locally label. This paper studies the relation between robust and local self-ordering. Curiously, this paper refutes the above intuition for bounded-degree graphs, and (weakly) confirms it for dense graphs. Roughly speaking, there are bounded degree graphs that are highly robustly self-ordered, for which any local self-ordering procedure requires \(\omega(\sqrt{n})\) queries. Moreover, there are bounded degree graphs with \(O(\log n)\)-query local self-ordering procedures, yet are not robustly self-ordered even for weak parameters. For dense graphs, the existence of fast non-adaptive local self-ordering procedures implies robust self-ordering.

Testing identity of collections of quantum states: sample complexity analysis by Marco Fanizza, Raffaele Salvia, and Vittorio Giovannetti (arXiv). This paper takes identity testing to the quantum setting. One should think of a \(d\)-dimensional quantum state as a \(d \times d\) density matrix (with some special properties). To learn the state entirely up to error \(\varepsilon\) would require \(O(\varepsilon^{-2} d^2)\) samples/measurements. A recent result of Badescu-O’Donnell-Wright proves that identity testing to a known state can be done significantly faster using \(O(\varepsilon^{-2} d)\) measurements. This paper takes this result a step further by consider a set of \(N\) quantum states. A “sample” is like a classical sample, where one gets a sample from a distribution of quantum states. The YES (“uniform”) case is when all the states are identical. The NO (“far from uniform”) case is when they are “far” from being the same state. This paper proves that \(O(\varepsilon^{-2}\sqrt{N}d)\) samples suffices for distinguishing these cases.