• Title/Summary/Keyword: Aluthge transform

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OPERATORS A, B FOR WHICH THE ALUTHGE TRANSFORM ${\tilde{AB}}$ IS A GENERALISED n-PROJECTION

  • Bhagwati P. Duggal;In Hyoun Kim
    • Bulletin of the Korean Mathematical Society
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    • v.60 no.6
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    • pp.1555-1566
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    • 2023
  • A Hilbert space operator A ∈ B(H) is a generalised n-projection, denoted A ∈ (G-n-P), if A*n = A. (G-n-P)-operators A are normal operators with finitely countable spectra σ(A), subsets of the set $\{0\}\,{\cup}\,\{\sqrt[n+1]{1}\}.$ The Aluthge transform à of A ∈ B(H) may be (G - n - P) without A being (G - n - P). For doubly commuting operators A, B ∈ B(H) such that σ(AB) = σ(A)σ(B) and ${\parallel}A{\parallel}\,{\parallel}B{\parallel}\;{\leq}\;{\parallel}{\tilde{AB}}{\parallel},$ ${\tilde{AB}}\;{\in}\;(G\,-\,n\,-\,P)$ if and only if $A\;=\;{\parallel}{\tilde{A}}{\parallel}\,(A_{00}\,{\oplus}\,(A_0\,{\oplus}\,A_u))$ and $B\;=\;{\parallel}{\tilde{B}}{\parallel}\,(B_0\,{\oplus}\,B_u),$ where A00 and B0, and A0 ⊕ Au and Bu, doubly commute, A00B0 and A0 are 2 nilpotent, Au and Bu are unitaries, A*nu = Au and B*nu = Bu. Furthermore, a necessary and sufficient condition for the operators αA, βB, αà and ${\beta}{\tilde{B}},\;{\alpha}\,=\,\frac{1}{{\parallel}{\tilde{A}}{\parallel}}$ and ${\beta}\,=\,\frac{1}{{\parallel}{\tilde{B}}{\parallel}},$ to be (G - n - P) is that A and B are spectrally normaloid at 0.

On the Iterated Duggal Transforms

  • Cho, Muneo;Jung, Il-Bong;Lee, Woo-Young
    • Kyungpook Mathematical Journal
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    • v.49 no.4
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    • pp.647-650
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    • 2009
  • For a bounded operator T = $U{\mid}T{\mid}$ (polar decomposition), we consider a transform b $\widehat{T}$ = ${\mid}T{\mid}U$ and discuss the convergence of iterated transform of $\widehat{T}$ under the strong operator topology. We prove that such iteration of quasiaffine hyponormal operator converges to a normal operator under the strong operator topology.