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A-Davis–Wielandt Radius Bounds of Semi-Hilbertian Space Operators

  • Messaoud Guesba,
  • Somdatta Barik,
  • Pintu Bhunia,
  • Kallol Paul

摘要

Consider \({\mathcal {H}}\) H is a complex Hilbert space and A is a positive operator on \({\mathcal {H}}.\) H . The mapping \(\langle \cdot ,\cdot \rangle _A: {\mathcal {H}}\times {\mathcal {H}} \rightarrow {\mathbb {C}}\) · , · A : H × H C , defined as \(\left\langle y,z\right\rangle _{A}=\left\langle Ay,z\right\rangle \) y , z A = A y , z for all yz \(\in \) \({{\mathcal {H}}}\) H , induces a seminorm \( \left\| \cdot \right\| _{A}\) · A . The A-Davis–Wielandt radius of an operator S on \({\mathcal {H}}\) H is defined as \(d\omega _{A}\left( S\right) =\sup \left\{ \sqrt{\left| \left\langle Sz,z\right\rangle _{A}\right| ^{2}+\left\| Sz\right\| _{A}^{4}} :\left\| z\right\| _{A}=1\right\} .\) d ω A S = sup S z , z A 2 + S z A 4 : z A = 1 . We investigate some new bounds for \(d\omega _{A}\left( S\right) \) d ω A S which refine the existing bounds. We also give some bounds for the \(2\times 2\) 2 × 2 off-diagonal block matrices.