Norm Inequalities for Commutators of Normal Operators

  • Fuad Kittaneh
Conference paper
Part of the International Series of Numerical Mathematics book series (ISNM, volume 157)


Let S, T, and X be bounded linear operators on a Hilbert space. It is shown that if S and T are normal with the Cartesian decompositions S = A+iC and T = B+iD such that a1Aa2, b1Bb2, c1Cc2, and d1Dd2 for some real numbers a1, a2, b1, b2, c1, c2, d1, and d2, then for every unitarily invariant norm |||·|||, and
$$ \left\| {ST - TS} \right\| \leqslant \frac{1} {2}\sqrt {(a_2 - a_1 )^2 + (c_2 - c_1 )^2 } \sqrt {(b_2 - b_1 )^2 + (d_2 - d_1 )^2 } , $$
where ‖·‖ is the usual operator norm. Applications of these norm inequalities are given, and generalizations of these inequalities to a larger class of nonnormal operators are also obtained.


Commutator normal operator positive operator unitarily invariant norm norm inequality Cartesian decomposition 


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Copyright information

© Birkhäuser Verlag Basel/Switzerland 2008

Authors and Affiliations

  • Fuad Kittaneh
    • 1
  1. 1.Department of MathematicsUniversity of JordanAmmanJordan

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