
doi: 10.1007/bf03323120
Set \(S_ \gamma^*\) denote the class of functions \(f(z)=z+\dots\) analytic in the unit disk \(\mathbb{D}\) such that \(\text{Re}[zf'(z)/f(z)]>\gamma\). The author shows that, if \(\alpha\geq 1\), \[ {{n+\alpha-1} \choose {n-1}}^{-1} \sum_{k=1}^ n {{n+\alpha-k} \choose {n-k}} {{2\gamma-2} \choose {k-1}}z^ k \in S_ \gamma^* \] for \(\gamma=(3-\alpha)/2\) but not for any smaller \(\gamma\). This result implies that, for any function \(f(z)=z+\dots\) analytic in \(\mathbb{D}\), \[ f\in S_{(3-\alpha)/2}^* \iff \forall n:\quad S_ n^ \alpha (z,f)\in S_{(3-\alpha)/2}^* \] where \(S_ n^ \alpha(z,f)\) is the Cesàro mean. It is conjectured that \[ \sigma_ n^ \alpha (z)={{n+\alpha} \choose n}^{-1} \sum_{k=0}^ n {{n+\alpha-k} \choose {n-k}}z^ k \] satisfies the subordination relation \(\sigma_ n^ \alpha(z)\prec \sigma_ n^ \beta (z)\) for \(2\leq\beta\leq\alpha\).
Special classes of univalent and multivalent functions of one complex variable (starlike, convex, bounded rotation, etc.), starlike, subordination, Cesàro means, Hadamard convolution
Special classes of univalent and multivalent functions of one complex variable (starlike, convex, bounded rotation, etc.), starlike, subordination, Cesàro means, Hadamard convolution
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