Logarithmic residues, generalized idempotents, and sums of idempotents in Banach algebras |
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Authors: | H Bart T Ehrhardt B Silbermann |
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Institution: | (1) Econometrisch Instituut, Erasmus Universiteit Rotterdam, Postbus 1738, 3000 DR Rotterdam, The Netherlands;(2) Fakultät für Mathematik, Technische Universität Chemnitz, PSF 964, 09009 Chemnitz, Germany |
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Abstract: | In a commutative Banach algebraB the set of logarithmic residues (i.e., the elements that can be written as a contour integral of the logarithmic derivative of an analyticB-valued function), the set of generalized idempotents (i.e., the elements that are annihilated by a polynomial with non-negative integer simple zeros), and the set of sums of idempotents are all the same. Also, these (coinciding) sets consist of isolated points only and are closed under the operations of addition and multiplication. Counterexamples show that the commutativity condition onB is essential. The results extend to logarithmic residues of meromorphicB-valued functions. |
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Keywords: | Primary: 46J05 30G30 16A32 Secondary: 46H95 |
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