#### Vol. 301, No. 1, 2019

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On the volume bound in the Dvoretzky–Rogers lemma

### Ferenc Fodor, Márton Naszódi and Tamás Zarnócz

Vol. 301 (2019), No. 1, 89–99
##### Abstract

The classical Dvoretzky–Rogers lemma provides a deterministic algorithm by which, from any set of isotropic vectors in Euclidean $d$-space, one can select a subset of $d$ vectors whose determinant is not too small. Pełczyński and Szarek improved this lower bound by a factor depending on the dimension and the number of vectors.

Pivovarov, on the other hand, determined the expectation of the square of the volume of parallelotopes spanned by $d$ independent random vectors in ${ℝ}^{d}$, each one chosen according to an isotropic measure. We extend Pivovarov’s result to a class of more general probability measures, which yields that the volume bound in the Dvoretzky–Rogers lemma is, in fact, equal to the expectation of the squared volume of random parallelotopes spanned by isotropic vectors. This allows us to give a probabilistic proof of the improvement of Pełczyński and Szarek, and provide a lower bound for the probability that the volume of such a random parallelotope is large.

##### Keywords
isotropic vectors, John's theorem, Dvoretzky–Rogers lemma, decomposition of the identity, volume
##### Mathematical Subject Classification 2010
Primary: 52A22, 52A38, 52A40, 52B11
##### Milestones
Received: 10 April 2018
Revised: 19 December 2018
Accepted: 19 December 2018
Published: 16 September 2019
##### Authors
 Ferenc Fodor Department of Geometry, Bolyai Institute University of Szeged Szeged Hungary Márton Naszódi Department of Geometry Eötvös University Budapest Hungary Tamás Zarnócz Bolyai Institute University of Szeged Szeged Hungary