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arXiv · 1105.4150

A Non-commutative Real Nullstellensatz Corresponds to a Non-commutative Real Ideal; Algorithms

Jaka Cimpric·Bill Helton·Scott McCullough·Christopher Nelson
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Abstract

This article takes up the challenge of extending the classical Real Nullstellensatz of Dubois and Risler to left ideals in a *-algebra A. After introducing the notions of non-commutative zero sets and real ideals, we develop three themes related to our basic question: does an element p of A having zero set containing the intersection of zero sets of elements from a finite set S of A belong to the smallest real ideal containing S? Firstly, we construct some general theory which shows that if a canonical topological closure of certain objects are permitted, then the answer is yes, while at the purely algebraic level it is no. Secondly for every finite subset S of the free *-algebra R of polynomials in g indeterminates and their formal adjoints, we give an implementable algorithm which computes the smallest real ideal containing S and prove that the algorithm succeeds in a finite number of steps. Lastly we provide examples of noncommutative real ideals for which a purely algebraic non-commutative real Nullstellensatz holds. For instance, this includes the real (left) ideals generated by a finite sets S in the *-algebra of n by n matrices whose entries are polynomials in one-variable. Further, explicit sufficient conditions on a left ideal in R are given which cover all the examples of such ideals of which we are aware and significantly more.

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Jaka Cimpric, Bill Helton, Scott McCullough, Christopher Nelson. 2012-02-11. A Non-commutative Real Nullstellensatz Corresponds to a Non-commutative Real Ideal; Algorithms. https://doi.org/10.1112/plms%2Fpds060

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