Isometries for Ky-Fan norms on block triangular matrix algebras (Q1423775)

Characterizing isometries of spaces of matrices or operators under various norms has been a fruitful area of research for a long time. In this article, the authors restrict their attention to finite dimensional spaces and to block upper triangular algebras of matrices they characterize the linear isometries for Ky-Fan norms on the space of block triangular matrices. Section 1 contains the main theorem. Section 2 contains proofs and related questions. The authors' theorem shows that a similar conclusion holds for surjective isometries for certain unitarily invariant norms on some triangular algebras.