MO1.R7.3

Explicit Good Codes Approaching Distance 1 in Ulam Metric

Elazar Goldenberg, The Academic College of Tel Aviv-Yaffo, Israel; Mursalin Habib, Karthik C. S., Rutgers University, United States

Session:
Combinatorial Coding Theory 1

Track:
1: Algebraic Aspects of Coding Theory

Location:
VIP

Presentation Time:
Mon, 8 Jul, 10:45 - 11:05

Session Chair:
Ago-Erik Riet,
Abstract
The Ulam distance of two permutations on [n] is n minus the length of their longest common subsequence. In this paper, we show that for every \varepsilon>0, there exists some \alpha>0, and an infinite set \Gamma \subseteq \mathbb{N}, such that for all n\in\Gamma, there is an explicit set C_n of (n!)^{\alpha} many permutations on [n], such that every pair of permutations in C_n has pairwise Ulam distance at least (1-\varepsilon) n. Moreover, we can compute the i^th permutation in C_n in poly(n) time and can also decode in poly(n) time, a permutation \pi on [n] to its closest permutation \pi^* in C_n, if the Ulam distance of \pi and \pi^* is less than (1-\varepsilon) n/4 . Previously, it was implicitly known by combining works of Goldreich and Wigderson [Israel Journal of Mathematics'23] and Farnoud, Skachek, and Milenkovic [IEEE Transactions on Information Theory'13] in a black-box manner, that it is possible to explicitly construct (n!)^{\Omega(1)} many permutations on [n], such that every pair of them have pairwise Ulam distance at least (1-\varepsilon) n/6, for any \varepsilon>0, and the bound on the distance can be improved to (1-\varepsilon) n/4 if the construction of Goldreich and Wigderson is directly analyzed in the Ulam metric.
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