Ordered algebra

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In mathematics, an ordered algebra is an algebra over the real numbers ${\displaystyle \mathbb {R} }$ with unit e together with an associated order such that e is positive (i.e. e ≥ 0), the product of any two positive elements is again positive, and when A is considered as a vector space over ${\displaystyle \mathbb {R} }$ then it is an Archimedean ordered vector space.

Let A be an ordered algebra with unit e and let C^* denote the cone in A^* (the algebraic dual of A) of all positive linear forms on A. If f is a linear form on A such that f(e) = 1 and f generates an extreme ray of C^* then f is a multiplicative homomorphism.^[1]

Stone's Algebra Theorem:^[1] Let A be an ordered algebra with unit e such that e is an order unit in A, let A^* denote the algebraic dual of A, and let K be the ${\displaystyle \sigma \left(A^{*},A\right)}$-compact set of all multiplicative positive linear forms satisfying f(e) = 1. Then under the evaluation map, A is isomorphic to a dense subalgebra of ${\displaystyle C_{\mathbb {R} }(X)}$. If in addition every positive sequence of type l¹ in A is order summable then A together with the Minkowski functional p_e is isomorphic to the Banach algebra ${\displaystyle C_{\mathbb {R} }(X)}$.

• Ordered vector space
• Riesz space

• Schaefer, Helmut H.; Wolff, Manfred P. (1999). Topological Vector Spaces. GTM. Vol. 3. New York, NY: Springer New York Imprint Springer. ISBN 978-1-4612-7155-0. OCLC 840278135.