Abstract
Let A be an n × n random matrix with i.i.d. entries of zero mean, unit variance and a bounded sub-Gaussian moment. We show that the condition number \(s_{\max }(A)/s_{\min }(A)\) satisfies the small ball probability estimate
where c > 0 may only depend on the sub-Gaussian moment. Although the estimate can be obtained as a combination of known results and techniques, it was not noticed in the literature before. As a key step of the proof, we apply estimates for the singular values of A, \({\mathbb P}\big \{s_{n-k+1}(A)\leq ck/\sqrt {n}\big \}\leq 2 \exp (-c k^2), \quad 1\leq k\leq n,\) obtained (under some additional assumptions) by Nguyen.
AMS 2010 Classification 60B20, 15B52, 46B06, 15A18
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Acknowledgements
The authors are grateful to the anonymous referee for careful reading and valuable suggestions that have helped to improve the presentation. The second named author would like to thank the Department of Mathematical and Statistical Sciences, University of Alberta for ideal working conditions.
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Litvak, A.E., Tikhomirov, K., Tomczak-Jaegermann, N. (2020). Small Ball Probability for the Condition Number of Random Matrices. In: Klartag, B., Milman, E. (eds) Geometric Aspects of Functional Analysis. Lecture Notes in Mathematics, vol 2266. Springer, Cham. https://doi.org/10.1007/978-3-030-46762-3_5
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