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Article . 1983
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Proceedings of the American Mathematical Society
Article . 1983 . Peer-reviewed
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Proceedings of the American Mathematical Society
Article . 1983 . Peer-reviewed
Data sources: Crossref
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A note on a problem of Robinson

Authors: Pearce, Kent;

A note on a problem of Robinson

Abstract

Let S \mathcal {S} be the usual class of univalent analytic functions on | z | > 1 \left | z \right | > 1 normalized by f ( 0 ) = 0 f(0) = 0 and f ′ ( 0 ) = 1 f’(0) = 1 . Let L \mathfrak {L} be the linear operator on S \mathcal {S} given by L f = 1 2 ( z f ) ′ \mathfrak {L}f = \tfrac {1}{2}(zf)’ and let r S t {r_{{\mathcal {S}_t}}} be the minimum radius of starlikeness of L f \mathfrak {L}f for f f in S \mathcal {S} . In 1947 R. M. Robinson initiated the study of properties of L \mathfrak {L} acting on S \mathcal {S} when he showed that r S t > .38 {r_{{\mathcal {S}_t}}} > .38 . Later, in 1975, R. W. Barnard gave an example which showed r S t > .445 {r_{{\mathcal {S}_t}}} > .445 . It is shown here, using a distortion theorem and Jenkin’s region of variability for z f ′ ( z ) / f ( z ) zf’(z)/f(z) , f f in S \mathcal {S} , that r S t > .435 {r_{{\mathcal {S}_t}}} > .435 . Also, a simple example, a close-to-convex half-line mapping, is given which again shows r S t > .445 {r_{{\mathcal {S}_t}}} > .445 .

Keywords

Special classes of univalent and multivalent functions of one complex variable (starlike, convex, bounded rotation, etc.), close-to-convex mapping, radius of starlikeness, distortion theorem, Robinson's one-half conjecture

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selected citations
These citations are derived from selected sources.
This is an alternative to the "Influence" indicator, which also reflects the overall/total impact of an article in the research community at large, based on the underlying citation network (diachronically).
BIP!Citations provided by BIP!
popularity
This indicator reflects the "current" impact/attention (the "hype") of an article in the research community at large, based on the underlying citation network.
BIP!Popularity provided by BIP!
influence
This indicator reflects the overall/total impact of an article in the research community at large, based on the underlying citation network (diachronically).
BIP!Influence provided by BIP!
impulse
This indicator reflects the initial momentum of an article directly after its publication, based on the underlying citation network.
BIP!Impulse provided by BIP!
2
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