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We present a new method for obtaining norm bounds for random matrices, where each entry is a low-degree polynomial in an underlying set of independent real-valued random variables. Such matrices arise in a variety of settings in the analysis of spectral and optimization algorithms, which require understanding the spectrum of a random matrix depending on data obtained as independent samples. Using ideas of decoupling and linearization from analysis, we show a simple way of expressing norm bounds for such matrices, in terms of matrices of lower-degree polynomials corresponding to derivatives. Iterating this method gives a simple bound with an elementary proof, which can recover many bounds previously required more involved techniques.
@InProceedings{tulsiani_et_al:LIPIcs.ITCS.2025.91,
author = {Tulsiani, Madhur and Wu, June},
title = {{Simple Norm Bounds for Polynomial Random Matrices via Decoupling}},
booktitle = {16th Innovations in Theoretical Computer Science Conference (ITCS 2025)},
pages = {91:1--91:22},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-361-4},
ISSN = {1868-8969},
year = {2025},
volume = {325},
editor = {Meka, Raghu},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.ITCS.2025.91},
URN = {urn:nbn:de:0030-drops-227194},
doi = {10.4230/LIPIcs.ITCS.2025.91},
annote = {Keywords: Matrix Concentration, Decoupling, Graph Matrices}
}