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Electronic Colloquium on Computational Complexity

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All reports by Author Prahladh Harsha:

TR17-181 | 26th November 2017
Irit Dinur, Yuval Filmus, Prahladh Harsha

Agreement tests on graphs and hypergraphs

Agreement tests are a generalization of low degree tests that capture a local-to-global phenomenon, which forms the combinatorial backbone of most PCP constructions. In an agreement test, a function is given by an ensemble of local restrictions. The agreement test checks that the restrictions agree when they overlap, and the ... more >>>

TR17-180 | 26th November 2017
Irit Dinur, Yuval Filmus, Prahladh Harsha

Low degree almost Boolean functions are sparse juntas

Nisan and Szegedy showed that low degree Boolean functions are juntas. Kindler and Safra showed that low degree functions which are *almost* Boolean are close to juntas. Their result holds with respect to $\mu_p$ for every *constant* $p$. When $p$ is allowed to be very small, new phenomena emerge. ... more >>>

TR17-013 | 23rd January 2017
Abhishek Bhrushundi, Prahladh Harsha, Srikanth Srinivasan

On polynomial approximations over $\mathbb{Z}/2^k\mathbb{Z}$

We study approximation of Boolean functions by low-degree polynomials over the ring $\mathbb{Z}/2^k\mathbb{Z}$. More precisely, given a Boolean function F$:\{0,1\}^n \rightarrow \{0,1\}$, define its $k$-lift to be F$_k:\{0,1\}^n \rightarrow \{0,2^{k-1}\}$ by $F_k(x) = 2^{k-F(x)}$ (mod $2^k$). We consider the fractional agreement (which we refer to as $\gamma_{d,k}(F)$) of $F_k$ with ... more >>>

TR16-204 | 20th December 2016
Prahladh Harsha, Srikanth Srinivasan

Robust Multiplication-based Tests for Reed-Muller Codes

We consider the following multiplication-based tests to check if a given function $f: \mathbb{F}_q^n\to \mathbb{F}_q$ is the evaluation of a degree-$d$ polynomial over $\mathbb{F}_q$ for $q$ prime.

* $\mathrm{Test}_{e,k}$: Pick $P_1,\ldots,P_k$ independent random degree-$e$ polynomials and accept iff the function $fP_1\cdots P_k$ is the evaluation of a degree-$(d+ek)$ polynomial.

... more >>>

TR16-160 | 26th October 2016
Irit Dinur, Prahladh Harsha, Rakesh Venkat, Henry Yuen

Multiplayer parallel repetition for expander games

Revisions: 1

We investigate the value of parallel repetition of one-round games with any number of players $k\ge 2$. It has been an open question whether an analogue of Raz's Parallel Repetition Theorem holds for games with more than two players, i.e., whether the value of the repeated game decays exponentially ... more >>>

TR16-068 | 28th April 2016
Prahladh Harsha, Srikanth Srinivasan

On Polynomial Approximations to $\mathrm{AC}^0$

Revisions: 1

We make progress on some questions related to polynomial approximations of $\mathrm{AC}^0$. It is known, by works of Tarui (Theoret. Comput. Sci. 1993) and Beigel, Reingold, and Spielman (Proc. $6$th CCC 1991), that any $\mathrm{AC}^0$ circuit of size $s$ and depth $d$ has an $\varepsilon$-error probabilistic polynomial over the reals ... more >>>

TR15-199 | 7th December 2015
Prahladh Harsha, Rahul Jain, Jaikumar Radhakrishnan

Relaxed partition bound is quadratically tight for product distributions

Let $f : \{0,1\}^n \times \{0,1\}^n \rightarrow \{0,1\}$ be a 2-party function. For every product distribution $\mu$ on $\{0,1\}^n \times \{0,1\}^n$, we show that $${{CC}}^\mu_{0.49}(f) = O\left(\left(\log {{rprt}}_{1/4}(f) \cdot \log \log {{rprt}}_{1/4}(f)\right)^2\right),$$ where ${{CC}^\mu_\varepsilon(f)$ is the distributional communication complexity with error at most $\varepsilon$ under the distribution $\mu$ and ... more >>>

TR15-085 | 23rd May 2015
Irit Dinur, Prahladh Harsha, Guy Kindler

Polynomially Low Error PCPs with polyloglogn Queries via Modular Composition

We show that every language in NP has a PCP verifier that tosses $O(\log n)$ random coins, has perfect completeness, and a soundness error of at most $1/poly(n)$, while making at most $O(poly\log\log n)$ queries into a proof over an alphabet of size at most $n^{1/poly\log\log n}$. Previous constructions that ... more >>>

TR13-167 | 28th November 2013
Venkatesan Guruswami, Prahladh Harsha, Johan Håstad, Srikanth Srinivasan, Girish Varma

Super-polylogarithmic hypergraph coloring hardness via low-degree long codes

We prove improved inapproximability results for hypergraph coloring using the low-degree polynomial code (aka, the “short code” of Barak et. al. [FOCS 2012]) and the techniques proposed by Dinur and Guruswami [FOCS 2013] to incorporate this code for inapproximability results.

In particular, we prove quasi-NP-hardness of the following problems on ... more >>>

TR09-144 | 24th December 2009
Prahladh Harsha, Adam Klivans, Raghu Meka

An Invariance Principle for Polytopes

Let $X$ be randomly chosen from $\{-1,1\}^n$, and let $Y$ be randomly
chosen from the standard spherical Gaussian on $\R^n$. For any (possibly unbounded) polytope $P$
formed by the intersection of $k$ halfspaces, we prove that
$$\left|\Pr\left[X \in P\right] - \Pr\left[Y \in P\right]\right| \leq \log^{8/5}k ... more >>>

TR09-042 | 5th May 2009
Irit Dinur, Prahladh Harsha

Composition of low-error 2-query PCPs using decodable PCPs

The main result of this paper is a simple, yet generic, composition theorem for low error two-query probabilistically checkable proofs (PCPs). Prior to this work, composition of PCPs was well-understood only in the constant error regime. Existing composition methods in the low error regime were non-modular (i.e., very much tailored ... more >>>

TR07-127 | 22nd November 2007
Arie Matsliah, Eli Ben-Sasson, Prahladh Harsha, Oded Lachish

Sound 3-query PCPPs are Long

We initiate the study of the tradeoff between the {\em length} of a
probabilistically checkable proof of proximity (PCPP) and the
maximal {\em soundness} that can be guaranteed by a $3$-query
verifier with oracle access to the proof. Our main observation is
that a verifier limited to querying a short ... more >>>

TR06-151 | 10th December 2006
Prahladh Harsha, Rahul Jain, David McAllester, Jaikumar Radhakrishnan

The communication complexity of correlation

We examine the communication required for generating random variables
remotely. One party Alice will be given a distribution D, and she
has to send a message to Bob, who is then required to generate a
value with distribution exactly D. Alice and Bob are allowed
to share random bits generated ... more >>>

TR04-021 | 23rd March 2004
Eli Ben-Sasson, Oded Goldreich, Prahladh Harsha, Madhu Sudan, Salil Vadhan

Robust PCPs of Proximity, Shorter PCPs and Applications to Coding

We continue the study of the trade-off between the length of PCPs
and their query complexity, establishing the following main results
(which refer to proofs of satisfiability of circuits of size $n$):
We present PCPs of length $\exp(\tildeO(\log\log n)^2)\cdot n$
that can be verified by making $o(\log\log n)$ Boolean queries.
more >>>

TR03-006 | 23rd January 2003
Eli Ben-Sasson, Prahladh Harsha, Sofya Raskhodnikova

3CNF Properties are Hard to Test

For a boolean formula \phi on n variables, the associated property
P_\phi is the collection of n-bit strings that satisfy \phi. We prove
that there are 3CNF properties that require a linear number of queries,
even for adaptive tests. This contrasts with 2CNF properties
that are testable with O(\sqrt{n}) ... more >>>

TR03-004 | 24th December 2002
Eli Ben-Sasson, Prahladh Harsha

Lower Bounds for Bounded-Depth Frege Proofs via Buss-Pudlack Games

We present a simple proof of the bounded-depth Frege lower bounds of
Pitassi et. al. and Krajicek et. al. for the pigeonhole
principle. Our method uses the interpretation of proofs as two player
games given by Pudlak and Buss. Our lower bound is conceptually
simpler than previous ones, and relies ... more >>>

TR00-061 | 14th August 2000
Prahladh Harsha, Madhu Sudan

Small PCPs with low query complexity

Most known constructions of probabilistically checkable proofs (PCPs)
either blow up the proof size by a large polynomial, or have a high
(though constant) query complexity. In this paper we give a
transformation with slightly-super-cubic blowup in proof size, with a
low query complexity. Specifically, the verifier probes the proof ... more >>>

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