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Eigenvalues, singular values, and Littlewood-Richardson coefficients

Sergey Fomin·William Fulton·Chi-Kwong Li·Yiu-Tung Poon
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Abstract

We characterize the relationship between the singular values of a complex Hermitian (resp., real symmetric, complex symmetric) matrix and the singular values of its off-diagonal block. We also characterize the eigenvalues of an Hermitian (or real symmetric) matrix C=A+B in terms of the combined list of eigenvalues of A and B. The answers are given by Horn-type linear inequalities. The proofs depend on a new inequality among Littlewood-Richardson coefficients.

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Sergey Fomin, William Fulton, Chi-Kwong Li, Yiu-Tung Poon. 2003-09-21. Eigenvalues, singular values, and Littlewood-Richardson coefficients. https://arxiv.org/abs/math/0301307

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