• Title/Summary/Keyword: doubly commuting

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A DOUBLY COMMUTING PAIR OF HYPONORMAL OPERATORS

  • Kim, Yong-Tae
    • Bulletin of the Korean Mathematical Society
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    • v.36 no.2
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    • pp.351-355
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    • 1999
  • If ($H_1$, $H_2$) is a doubly commuting pair of hyponormal operators on a Hilbert spaces H, then there exists a commuting pair ($T_1$,$T_1$) of contractions on H such that $H_i$=$H_i^*$$T_i$ for each i=1,2.

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ON THE JOINT WEYL AND BROWDER SPECTRA OF HYPONORMAL OPERTORS

  • Lee, Young-Yoon
    • Communications of the Korean Mathematical Society
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    • v.16 no.2
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    • pp.235-241
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    • 2001
  • In this paper we study some properties of he joint Weyl and Browder spectra for the slightly larger classes containing doubly commuting n-tuples of hyponormal operators.

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ON JOINT WEYL AND BROWDER SPECTRA

  • Kim, Jin-Chun
    • Bulletin of the Korean Mathematical Society
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    • v.37 no.1
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    • pp.53-62
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    • 2000
  • In this paper we explore relations between joint Weyl and Browder spectra. Also, we give a spectral characterization of the Taylor-Browder spectrum for special classes of doubly commuting n-tuples of operators and then give a partial answer to Duggal's question.

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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.