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Noncoherence of some rings of functions. (English) Zbl 1123.46036

Let \({\mathbf f}=\left( f_1,\dots ,f_n\right)\) be an \(n\)-tuple of elements of a unital commutative ring \(R\) and define \({\mathbf f}^\perp\) to be the set of \(n\)-tuples \(\left( g_1,\dots,g_n\right)\) of elements of \(R\) such that \(g_1f_1+\cdots +g_nf_n=0\). The ring \(R\) is said to be coherent if, for each natural number \(n\) and each \(n\)-tuple \({\mathbf f}\), the set \({\mathbf f}^\perp\) is finitely generated in the sense that there exist elements \({\mathbf g}_1,\dots ,{\mathbf g}_d\) in \({\mathbf f}^\perp\) such that every element \({\mathbf g}\) in \({\mathbf f}^\perp\) has the form \({\mathbf g}= r_1{\mathbf g}_1 +\cdots +r_d{\mathbf g}_d\) for some elements \(r_1,\dots,r_d\) in \(R\). In [J. Funct.Anal.21, 76–87 (1976; Zbl 0317.46049)], W.S.McVoy and L.A.Rubel showed that \(H^\infty\) is coherent while the disk algebra \(A\) is not. More generally, if \(S\) is a subset of the circle \({\mathbf T}\), then the algebra \(A_S\) consisting of those functions that are analytic on the disk \({\mathbf D}\) and continuous and bounded on \({\mathbf D}\cup S\) lies between \(A=A_{\mathbf T}\) and \(H^\infty=A_\emptyset\). In this paper, the author uses similar techniques to show that, if the set \(S\) contains any of its limit points, then the algebra \(A_S\) is not coherent. It remains an open question whether the converse statement is true or not.

MSC:

46J15 Banach algebras of differentiable or analytic functions, \(H^p\)-spaces
46E25 Rings and algebras of continuous, differentiable or analytic functions
93C05 Linear systems in control theory
13E15 Commutative rings and modules of finite generation or presentation; number of generators

Citations:

Zbl 0317.46049
Full Text: DOI

References:

[1] Jacqueline Détraz, Étude du spectre d’algèbres de fonctions analytiques sur le disque unité, C. R. Acad. Sci. Paris Sér. A-B 269 (1969), A833 – A835 (French). · Zbl 0181.14401
[2] Sarah Glaz, Commutative coherent rings: historical perspective and current developments, Nieuw Arch. Wisk. (4) 10 (1992), no. 1-2, 37 – 56. · Zbl 0787.13001
[3] Kenneth Hoffman, Banach spaces of analytic functions, Dover Publications, Inc., New York, 1988. Reprint of the 1962 original. · Zbl 0734.46033
[4] Marjan Jerman, When is \?(\?) a po-coherent ring?, Comm. Algebra 30 (2002), no. 4, 1949 – 1959. · Zbl 1026.46034 · doi:10.1081/AGB-120013225
[5] W. S. McVoy and L. A. Rubel, Coherence of some rings of functions, J. Functional Analysis 21 (1976), no. 1, 76 – 87. · Zbl 0317.46049
[6] Charles W. Neville, When is \?(\?) a coherent ring?, Proc. Amer. Math. Soc. 110 (1990), no. 2, 505 – 508. · Zbl 0719.54019
[7] A. Quadrat, The fractional representation approach to synthesis problems: an algebraic analysis viewpoint. I. (Weakly) doubly coprime factorizations, SIAM J. Control Optim. 42 (2003), no. 1, 266 – 299. · Zbl 1035.93017 · doi:10.1137/S0363012902417127
[8] A. Quadrat, The fractional representation approach to synthesis problems: an algebraic analysis viewpoint. II. Internal stabilization, SIAM J. Control Optim. 42 (2003), no. 1, 300 – 320. · Zbl 1035.93018 · doi:10.1137/S0363012902417139
[9] Walter Rudin, Real and complex analysis, 3rd ed., McGraw-Hill Book Co., New York, 1987. · Zbl 0925.00005
[10] A.J. Sasane. Irrational transfer function classes, coprime factorization and stabilization. CDAM Research Report CDAM-LSE-2005-10, May 2005. Available electronically at http://www.cdam.lse.ac.uk/Reports/Files/cdam-2005-10.pdf
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