Oded Goldreich

We consider the problem of estimating the average of a huge set of values.

That is,

given oracle access to an arbitrary function $f:\{0,1\}^n\mapsto[0,1]$,

we need to estimate $2^{-n} \sum_{x\in\{0,1\}^n} f(x)$

upto an additive error of $\epsilon$.

We are allowed to employ a randomized algorithm which may ...
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Ziv Bar-Yossef, Oded Goldreich, Avi Wigderson

This paper initiates the study of deterministic amplification of space

bounded probabilistic algorithms. The straightforward implementations of

known amplification methods cannot be used for such algorithms, since they

consume too much space. We present a new implementation of the

Ajtai-Koml\'{o}s-Szemer\'{e}di method, that enables to amplify an $S$ ...
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Ran Raz, Omer Reingold, Salil Vadhan

We give explicit constructions of extractors which work for a source of

any min-entropy on strings of length n. These extractors can extract any

constant fraction of the min-entropy using O(log^2 n) additional random

bits, and can extract all the min-entropy using O(log^3 n) additional

random bits. Both of these ...
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Oded Goldreich

We suggest a candidate one-way function using combinatorial

constructs such as expander graphs. These graphs are used to

determine a sequence of small overlapping subsets of input bits,

to which a hard-wired random predicate is applied.

Thus, the function is extremely easy to evaluate:

all that is needed ...
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Omer Reingold, Salil Vadhan, Avi Wigderson

The main contribution of this work is a new type of graph product, which we call the zig-zag

product. Taking a product of a large graph with a small graph, the resulting graph inherits

(roughly) its size from the large one, its degree from the small one, and ...
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Luca Trevisan, Salil Vadhan, David Zuckerman

We study the compression of polynomially samplable sources. In particular, we give efficient prefix-free compression and decompression algorithms for three classes of such sources (whose support is a subset of {0,1}^n).

1. We show how to compress sources X samplable by logspace machines to expected length H(X)+O(1).

Our next ... more >>>

Omer Reingold, Luca Trevisan, Salil Vadhan

Motivated by Reingold's recent deterministic log-space algorithm for Undirected S-T Connectivity (ECCC TR 04-94), we revisit the general RL vs. L question, obtaining the following results.

1. We exhibit a new complete problem for RL: S-T Connectivity restricted to directed graphs for which the random walk is promised to have ... more >>>

Ronen Gradwohl, Guy Kindler, Omer Reingold, Amnon Ta-Shma

Optimal dispersers have better dependence on the error than

optimal extractors. In this paper we give explicit disperser

constructions that beat the best possible extractors in some

parameters. Our constructions are not strong, but we show that

having such explicit strong constructions implies a solution

to the Ramsey graph construction ...
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Eyal Rozenman, Salil Vadhan

We introduce a "derandomized" analogue of graph squaring. This

operation increases the connectivity of the graph (as measured by the

second eigenvalue) almost as well as squaring the graph does, yet only

increases the degree of the graph by a constant factor, instead of

squaring the degree.

One application of ... more >>>

Oded Goldreich

We highlight a common theme in four relatively recent works

that establish remarkable results by an iterative approach.

Starting from a trivial construct,

each of these works applies an ingeniously designed

sequence of iterations that yields the desired result,

which is highly non-trivial. Furthermore, in each iteration,

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Alexander Healy

We construct a randomness-efficient averaging sampler that is computable by uniform constant-depth circuits with parity gates (i.e., in AC^0[mod 2]). Our sampler matches the parameters achieved by random walks on constant-degree expander graphs, allowing us to apply a variety expander-based techniques within NC^1. For example, we obtain the following results:

... more >>>Yonatan Bilu, Nathan Linial

We introduce the notion of a stable instance for a discrete

optimization problem, and argue that in many practical situations

only sufficiently stable instances are of interest. The question

then arises whether stable instances of NP--hard problems are

easier to solve. In particular, whether there exist algorithms

that solve correctly ...
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Vikraman Arvind, Srikanth Srinivasan

Using $\epsilon$-bias spaces over F_2 , we show that the Remote Point Problem (RPP), introduced by Alon et al [APY09], has an $NC^2$ algorithm (achieving the same parameters as [APY09]). We study a generalization of the Remote Point Problem to groups: we replace F_n by G^n for an arbitrary fixed ... more >>>

Zeev Dvir, Avi Wigderson

The main purpose of this work is to formally define monotone expanders and motivate their study with (known and new) connections to other graphs and to several computational and pseudorandomness problems. In particular we explain how monotone expanders of constant degree lead to:

(1) Constant degree dimension expanders in finite ...
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Oded Goldreich

Contemplating the recently announced 1-local expanders of Viola and Wigderson (ECCC, TR16-129, 2016), one may observe that weaker constructs are well know. For example, one may easily obtain a 4-regular $N$-vertex graph with spectral gap that is $\Omega(1/\log^2 N)$, and similarly a $O(1)$-regular $N$-vertex graph with spectral gap $1/\tildeO(\log N)$.

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