A Near-cubic Lower Bound for 3-query Locally Decodable Codes

Date: October 6, 2022
Time: 4:00 pm
Room: DBH 4011
Speaker: Venkatesan Guruswami 
(UC Berkeley)

Locally decodable codes (LDCs) allow for ultra-efficient recovery of
any single message symbol by querying a very few codeword symbols. In
addition to their appeal for storage and cryptographic applications,
locality is a fundamental concept in coding theory with many
ramifications across computational complexity. An outstanding
challenge concerning LDCs is their optimal encoding length for a
desired number q of queries. For q=2, it is known that exponential
blow-up in encoding length is necessary (and the simple Hadamard code
achieves this). For q > 2, however, there are significant gaps in our
understanding. For instance, for 3-query LDCs, the best constructions
require sub-exponential encoding length, and the best known lower
bound, that has stood for two decades, was only quadratic.

In this talk, we will describe a near-cubic lower bound on the
encoding length of 3-query LDCs. The approach is inspired by and
borrows from recent advances in refuting semi-random instances of
constraint satisfaction problems.

Based on joint work with Omar Alrabiah, Pravesh Kothari, and Peter Manohar.


Venkatesan Guruswami is a Professor of Computer Science at UC Berkeley
and senior scientist at the Simons Institute for the Theory of
Computing. Venkat received his Bachelor’s degree from the Indian
Institute of Technology, Madras, and his Ph.D. from MIT.

Venkat’s research interests include coding theory, approximability of
optimization problems, and computational complexity. He is the
Editor-in-Chief of JACM, and was previously Editor-in-Chief of the ACM
Transactions on Computation Theory and the president of the
Computational Complexity Foundation. Venkat was a co-winner of the
2012 Presburger Award, and his other honors include a Simons
Investigator award, Packard and Sloan Fellowships, the ACM Doctoral
Dissertation Award, and an IEEE Information Theory Society Paper
Award. He is a fellow of the ACM and the IEEE.

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