# Paper ID sheet UCL-INMA-2012.07

Title

## Low-rank matrix completion via preconditioned optimization on the Grassmann manifold

Authors
Nicolas Boumal, P.-A. Absil
Abstract
We address the numerical problem of recovering large matrices of low rank when most of the entries are unknown. We exploit the geometry of the low-rank constraint to recast the problem as an unconstrained optimization problem on a single Grassmann manifold. We then apply second-order Riemannian trust-region methods (RTRMC 2) and Riemannian conjugate gradient methods (RCGMC) to solve it. A preconditioner for the Hessian is introduced that helps control the conditioning of the problem and we detail preconditioned versions of Riemannian optimization algorithms. The cost of each iteration is linear in the number of known entries. The proposed methods are competitive with state-of-the-art algorithms on a wide range of problem instances. In particular, they perform well on rectangular matrices. We further note that second-order and preconditioned methods are well suited to solve badly conditioned matrix completion tasks.
Key words
low-rank matrix completion; optimization on manifolds; Grassmann manifold; preconditioned Riemannian trust-regions; preconditioned Riemannian conjugate gradient; second-order methods; fixed-rank geometry; RTRMC; RCGMC
Status
Linear Algebra and its Applications, 475, pp. 200-239, 2015
BibTeX entry

@Article{boumal2015rtrmcextended,
Title                    = {Low-rank matrix completion via preconditioned optimization on the {G}rassmann manifold},
Author                   = {Boumal, N. and Absil, P.-A.},
Journal                  = {Linear Algebra and its Applications},
Year                     = {2015},
Pages                    = {200--239},
Volume                   = {475},

Doi                      = {10.1016/j.laa.2015.02.027},
Url                      = {http://www.sciencedirect.com/science/article/pii/S0024379515001342}
}

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