
Let \(S\) be the class of functions \(f:f(z)= z+\sum^\infty_{k=2} a_kz^k\) that are analytic in the unit disc \(E\). Let \(S^*(\alpha)\) and \(K(\alpha)\), respectively, be the subclasses of \(S\) which consist of starlike and convex functions of order \(\alpha, 0\leq\alpha <1\). A sufficient condition for \(f\) to be in \(S^*(\alpha)\) is that \(\sum^\infty_{k=2} (k-\alpha) | a_k |\leq 1-\alpha\) and to be in \(K(\alpha)\) is that \(\sum^\infty_{k=2} K(k-\alpha) | a_k|\leq 1- \alpha.\) In this paper, the ratio of a function \(f\) to its sequence of partial sums \(f_n(z)= z+ \sum^n_{k=2} a_kz^k\) is studied when the coefficients of \(f\) are sufficiently small to satisfy one of these conditions. Sharp lower bounds for \(\text{Re} \left\{{f(z) \over f_n(z)}\right\}\), \(\text{Re} \left\{{f_n(z) \over f(z)}\right\}\), \(\text{Re} \left\{{f'(z) \over f_n'(z)}\right\}\) and \(\text{Re} \left\{ {f_n'(z) \over f'(z)}\right\}\) are determined when the coefficients \(\{a_k\}\) are small.
Special classes of univalent and multivalent functions of one complex variable (starlike, convex, bounded rotation, etc.), convex functions, partial sums, Applied Mathematics, starlike, Analysis
Special classes of univalent and multivalent functions of one complex variable (starlike, convex, bounded rotation, etc.), convex functions, partial sums, Applied Mathematics, starlike, Analysis
| 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). | 90 | |
| 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. | Top 1% | |
| influence This indicator reflects the overall/total impact of an article in the research community at large, based on the underlying citation network (diachronically). | Top 1% | |
| impulse This indicator reflects the initial momentum of an article directly after its publication, based on the underlying citation network. | Average |
