Function Algebra
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Function Algebra

In functional analysis, a Banach function algebra on a compact Hausdorff space X is unital subalgebra, A, of the commutative C*-algebra C(X) of all continuous, complex-valued functions from X, together with a norm on A that makes it a Banach algebra.

A function algebra is said to vanish at a point p if f(p) = 0 for all . A function algebra separates points if for each distinct pair of points , there is a function such that .

For every define for . Then is a homomorphism (character) on , non-zero if does not vanish at .

Theorem: A Banach function algebra is semisimple (that is its Jacobson radical is equal to zero) and each commutative unital, semisimple Banach algebra is isomorphic (via the Gelfand transform) to a Banach function algebra on its character space (the space of algebra homomorphisms from A into the complex numbers given the relative weak* topology).

If the norm on is the uniform norm (or sup-norm) on , then is called a uniform algebra. Uniform algebras are an important special case of Banach function algebras.


  • Andrew Browder (1969) Introduction to Function Algebras, W. A. Benjamin
  • H.G. Dales (2000) Banach Algebras and Automatic Continuity, London Mathematical Society Monographs 24, Clarendon Press ISBN 0-19-850013-0
  • Graham Allan & H. Garth Dales (2011) Introduction to Banach Spaces and Algebras, Oxford University Press ISBN 978-0-19-920654-4

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