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On the complete boundedness of the Schur block product (1712.05285v3)
Published 14 Dec 2017 in math.OA, math-ph, math.MP, and math.QA
Abstract: We give a Stinespring representation of the Schur block product, say (), on pairs of square matrices with entries in a C-algebra as a completely bounded bilinear operator of the form: A:=(a_{ij}), B:= (b_{ij}): A () B := (a_{ij}b_{ij}) = V pi(A) F pi(B) V, such that V is an isometry, pi is a -representation and F is a self-adjoint unitary. This implies an inequality due to Livshits and two apparently new ones on diagonals of matrices. ||A () B|| \leq ||A||_r ||B||_c operator, row and column norm; - diag(A*A) \leq A* () A \leq diag(A*A), and for all vectors f, g: |<A()B f,g> |2 \leq < diag(AA*) g, g> <diag(B*B) f,f> .