Index of Hadamard multiplication by positive matrices II
For each n×n positive semidefinite matrix A we define the minimal index I(A)=max{λ≥0:A∘B≥λB for all B≥0} and, for each norm N, the N-index I<SUB>N</SUB>(A)=min{N(A∘B):B≥0 and N(B)=1}, where A ∘ B=[a<SUB>ij</SUB>b<SUB>ij</SUB>] is the Hadamard or Schur product of A...
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| Autores principales: | , |
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| Formato: | Articulo |
| Lenguaje: | Inglés |
| Publicado: |
2001
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| Materias: | |
| Acceso en línea: | http://sedici.unlp.edu.ar/handle/10915/84728 |
| Aporte de: |
| Sumario: | For each n×n positive semidefinite matrix A we define the minimal index I(A)=max{λ≥0:A∘B≥λB for all B≥0} and, for each norm N, the N-index I<SUB>N</SUB>(A)=min{N(A∘B):B≥0 and N(B)=1}, where A ∘ B=[a<SUB>ij</SUB>b<SUB>ij</SUB>] is the Hadamard or Schur product of A=[a<SUB>ij</SUB>] and B=[b<SUB>ij</SUB>] and B≥0 means that B is a positive semidefinite matrix. A comparison between these indexes is done, for different choices of the norm N. As an application we find, for each bounded invertible selfadjoint operator S on a Hilbert space, the best constant M(S) such that ∥STS+S<SUP>-1</SUP>TS<SUP>-1</SUP>∥≥M(S)∥T∥ for all T≥0. |
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