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Quarterly of Applied Mathematics

Quarterly of Applied Mathematics

Online ISSN 1552-4485; Print ISSN 0033-569X

   
 
 

 

The conjugate gradient algorithm on well-conditioned Wishart matrices is almost deterministic


Authors: Percy Deift and Thomas Trogdon
Journal: Quart. Appl. Math. 79 (2021), 125-161
MSC (2010): Primary 65F10, 60B20
DOI: https://doi.org/10.1090/qam/1574
Published electronically: July 9, 2020
MathSciNet review: 4188626
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Abstract: We prove that the number of iterations required to solve a random positive definite linear system with the conjugate gradient algorithm is almost deterministic for large matrices. We treat the case of Wishart matrices $W = XX^*$ where $X$ is $n \times m$ and $n/m \sim d$ for $0 < d < 1$. Precisely, we prove that for most choices of error tolerance, as the matrix increases in size, the probability that the iteration count deviates from an explicit deterministic value tends to zero. In addition, for a fixed iteration count, we show that the norm of the error vector and the norm of the residual converge exponentially fast in probability, converge in mean, and converge almost surely.


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Additional Information

Percy Deift
Affiliation: New York University, Courant Institute of Mathematical Sciences, 251 Mercer St., New York, New York 10012
MR Author ID: 56085
Email: deift@cims.nyu.edu

Thomas Trogdon
Affiliation: Department of Applied Mathematics, University of Washington, Seattle, Washington 98195-3925
MR Author ID: 965414
ORCID: 0000-0002-6955-4154
Email: trogdon@uw.edu

Received by editor(s): April 27, 2020
Published electronically: July 9, 2020
Additional Notes: This work was supported in part by NSF DMS-1300965 (PD) and NSF DMS-1753185, DMS-1945652 (TT)
Article copyright: © Copyright 2020 Brown University