Approximation by Unimodular Functions
The theorems in this paper are all concerned with either pointwise or uniform approximation by functions which have unit modulus or by convex combinations of such functions. The results are related to, and are outgrowths of, the theorems in [4; 5; 10]. In § 1, we show that a function bounded by 1, w...
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| Veröffentlicht in: | Canadian journal of mathematics Jg. 23; H. 2; S. 257 - 269 |
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| 1. Verfasser: | |
| Format: | Journal Article |
| Sprache: | Englisch |
| Veröffentlicht: |
Cambridge, UK
Cambridge University Press
01.04.1971
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| ISSN: | 0008-414X, 1496-4279 |
| Online-Zugang: | Volltext |
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| Zusammenfassung: | The theorems in this paper are all concerned with either pointwise or uniform approximation by functions which have unit modulus or by convex combinations of such functions. The results are related to, and are outgrowths of, the theorems in [4; 5; 10]. In § 1, we show that a function bounded by 1, which is analytic in the open unit disc Δ and continuous on may be approximated uniformly on the set where it has modulus 1 (subject to certain restrictions; see Theorem 1) by a finite Blaschke product; that is, by a function of the form
*
where |λ| = 1 and |αi
| < 1, i = 1, …, N. In § 1 we also discuss pointwise approximation by Blaschke products with restricted zeros. |
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| ISSN: | 0008-414X 1496-4279 |
| DOI: | 10.4153/CJM-1971-025-4 |