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LavaCircus (talk | contribs) Some results in OA are phrased analytically, and some theories use incredibly algebraic proofs. For example subfactor theory often uses fusion categories to prove results. I added "often" twice to the first sentence of the second paragraph. Tags: Mobile edit Mobile web edit |
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Though algebras of operators are studied in various contexts (for example, algebras of [[pseudo-differential operator]]s acting on spaces of [[Distribution (mathematics)|distributions]]), the term ''operator algebra'' is usually used in reference to algebras of [[bounded operator]]s on a [[Banach space]] or, even more specially in reference to algebras of operators on a [[Separable space|separable]] [[Hilbert space]], endowed with the [[operator norm]] topology.
In the case of operators on a Hilbert space, the [[Hermitian adjoint]] map on operators gives a natural [[Involution (mathematics)|involution]], which provides an additional algebraic structure that can be imposed on the algebra. In this context, the best studied examples are [[self-adjoint]] operator algebras, meaning that they are closed under taking adjoints. These include [[C*-algebra]]s, [[von Neumann algebra]]s, and [[AW*-algebra]]s. C*-algebras can be easily characterized abstractly by a condition relating the norm, involution and multiplication. Such abstractly defined C*-algebras can be identified to a certain closed [[Subalgebra#Subalgebras for algebras over a ring or field|subalgebra]] of the algebra of the continuous linear operators on a suitable Hilbert space. A similar result holds for von Neumann algebras.
[[commutative algebra|Commutative]] self-adjoint operator algebras can be regarded as the algebra of [[Complex numbers|complex]]-valued continuous functions on a [[locally compact space]], or that of [[measurable function]]s on a [[measurable space|standard measurable space]]. Thus, general operator algebras are often regarded as a noncommutative generalizations of these algebras, or the structure of the ''base space'' on which the functions are defined. This point of view is elaborated as the philosophy of [[noncommutative geometry]], which tries to study various non-classical and/or pathological objects by noncommutative operator algebras.
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