Vojtech Dvorák

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2ranked-venue papers
2as first author
1since 2021 · last 2022
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Theory of computation · 2 · 2 first-author · 1 since 2021
YearPublicationVenuePosition
2022 Probability Mass of Rademacher Sums Beyond One Standard Deviation
abstract
Let $a_1, \ldots, a_n \in \mathbb{R}$ satisfy $\sum_i a_i^2 = 1$, and let $\varepsilon_1, \ldots, \varepsilon_n$ be uniformly random $\pm 1$ signs and $X = \sum_{i=1}^{n} a_i \varepsilon_i$. It is conjectured that $X = \sum_{i=1}^{n} a_i \varepsilon_i$ has $\Pr[X \geq 1] \geq 7/64$. The best lower bound so far is $1/20$, due to Oleszkiewicz. In this paper we improve this to $\Pr[X \geq 1] \geq 6/64$.
Vojtech Dvorák, Ohad Klein
SIAM J. Discret. Math.1
2020 Improved Bound for Tomaszewski's Problem
abstract
In 1986, Tomaszewski made the following conjecture. Given $n$ real numbers $a_{1},\ldots,a_{n}$ with $\sum_{i=1}^{n}a_{i}^{2}=1$, then of the $2^{n}$ signed sums $\pm a_{1} \pm \cdots \pm a_{n}$, at least half have absolute value at most 1. Hendriks and van Zuijlen [ An Improvement of the Boppana-Holzman Bound for Rademacher Random Variables}, arXiv:2003.02588, 2020] and Boppana, Hendriks, and van Zuijlen [ Tomaszewski's Problem on Randomly Signed Sums, Revisited, arXiv:2003.06433, 2020] independently proved that a proportion of at least 0.4276 of these sums has absolute value at most 1. Using different techniques, we improve this bound to 0.46.
Vojtech Dvorák, Peter van Hintum, Marius Tiba
SIAM J. Discret. Math.1