Trace-Class Operator
Let H be a Hilbert space and (e_i)_(i in I) an orthonormal basis for H. The set of all products of two Hilbert-Schmidt operators is denoted N(H), and its elements are called trace-class operators. This set is a self-adjoint two-sided ideal of B(H) and coincides with the set of those operators T for which sum_(i in I)<|T|e_i,e_i><infty where |T| is the absolute value of T in the C^*-algebra B(H). If ||T||_1=sum_(i in I)<|T|e_i,e_i>, then N(H) with this norm is a Banach algebra in which F(H) is dense. Furthermore, N(H) subset S(H) subset K(H).
See also
Hilbert-Schmidt OperatorThis entry contributed by Mohammad Sal Moslehian
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References
Gohberg, I. C. and Kreǐn, M. G. Introduction to the Theory of Linear Nonselfadjoint Operators. Providence, RI: Amer. Math. Soc., 1969.Murphy, G. J. C-*-Algebras and Operator Theory. New York: Academic Press, 1990.Referenced on Wolfram|Alpha
Trace-Class OperatorCite this as:
Moslehian, Mohammad Sal. "Trace-Class Operator." From MathWorld--A Wolfram Resource, created by Eric W. Weisstein. https://mathworld.wolfram.com/Trace-ClassOperator.html