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Fan, K. (1949) On a Theorem of Weyl Concerning Eigenvalues of Linear Transformations I. Proceedings of the National Academy of Sciences of the United States of America, 35, 652-655.
https://doi.org/10.1073/pnas.35.11.652

has been cited by the following article:

• TITLE: Maximum Principles for Normal Matrices

  AUTHORS: Achiya Dax

  KEYWORDS: Ky Fan Maximum Principle, Normal Matrices, Extended Maximum Principle, Unitarily Invariant Norms

  JOURNAL NAME: Advances in Linear Algebra & Matrix Theory, Vol.9 No.3, September 30, 2019

  ABSTRACT: Ky Fan maximum principle is a well-known observation about traces of certain hermitian matrices. In this note, we derive a powerful extension of this claim. The extension is achieved in three ways. First, traces are replaced with norms of diagonal matrices, and any unitarily invariant norm can be used. Second, hermitian matrices are replaced by normal matrices, so the rule applies to a larger class of matrices. Third, diagonal entries can be replaced with eigenvalues and singular values. It is shown that the new maximum principle is closely related to the problem of approximating one matrix by another matrix of a lower rank.