Sharp error bounds for Ritz vectors and approximate singular vectors

Yuji Nakatsukasa

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arXiv · 1810.02532

Sharp error bounds for Ritz vectors and approximate singular vectors

Yuji Nakatsukasa

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Abstract

We derive sharp bounds for the accuracy of approximate eigenvectors (Ritz vectors) obtained by the Rayleigh-Ritz process for symmetric eigenvalue problems. Using information that is available or easy to estimate, our bounds improve the classical Davis-Kahan $\sin\theta$ theorem by a factor that can be arbitrarily large, and can give nontrivial information even when the $\sin\theta$ theorem suggests that a Ritz vector might have no accuracy at all. We also present extensions in three directions, deriving error bounds for invariant subspaces, singular vectors and subspaces computed by a (Petrov-Galerkin) projection SVD method, and eigenvectors of self-adjoint operators on a Hilbert space.

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Yuji Nakatsukasa. 2018-10-05. Sharp error bounds for Ritz vectors and approximate singular vectors. https://arxiv.org/abs/1810.02532

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