<p>Inverse logarithmic coefficients play an important role in the theory of univalent functions. In this paper, we obtain sharp bounds for the inverse logarithmic coefficients associated with the class <InlineEquation ID="IEq3"> <EquationSource Format="TEX">\(\mathcal {S}_e^*\)</EquationSource> <EquationSource Format="MATHML"><math> <msubsup> <mi mathvariant="script">S</mi> <mi>e</mi> <mo>∗</mo> </msubsup> </math></EquationSource> </InlineEquation> of starlike functions defined by the subordination condition <Equation ID="Equ41"> <EquationSource Format="TEX">\( \mathcal {S}_e^*:= \left\{ f \in \mathcal {S} : \frac{z f'(z)}{f(z)} \prec e^z,\; z \in \mathbb {D} \right\} . \)</EquationSource> <EquationSource Format="MATHML"><math display="block"> <mrow> <msubsup> <mi mathvariant="script">S</mi> <mi>e</mi> <mo>∗</mo> </msubsup> <mo>:</mo> <mo>=</mo> <mfenced close="}" open="{"> <mi>f</mi> <mo>∈</mo> <mi mathvariant="script">S</mi> <mo>:</mo> <mfrac> <mrow> <mi>z</mi> <msup> <mi>f</mi> <mo>′</mo> </msup> <mrow> <mo stretchy="false">(</mo> <mi>z</mi> <mo stretchy="false">)</mo> </mrow> </mrow> <mrow> <mi>f</mi> <mo stretchy="false">(</mo> <mi>z</mi> <mo stretchy="false">)</mo> </mrow> </mfrac> <mo>≺</mo> <msup> <mi>e</mi> <mi>z</mi> </msup> <mo>,</mo> <mspace width="0.277778em" /> <mi>z</mi> <mo>∈</mo> <mi mathvariant="double-struck">D</mi> </mfenced> <mo>.</mo> </mrow> </math></EquationSource> </Equation>We further derive sharp estimates for the Hankel determinants constructed from these inverse logarithmic coefficients for functions in the class <InlineEquation ID="IEq4"> <EquationSource Format="TEX">\(\mathcal {S}_e^*\)</EquationSource> <EquationSource Format="MATHML"><math> <msubsup> <mi mathvariant="script">S</mi> <mi>e</mi> <mo>∗</mo> </msubsup> </math></EquationSource> </InlineEquation>. In addition, we investigate the inverse logarithmic coefficient difference problem for this class. In each case, the obtained bounds are shown to be sharp, and the corresponding extremal functions are explicitly determined.</p>

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Sharp bounds for inverse logarithmic coefficients and Hankel determinants for the class \(\mathcal {S}_e^*\)

  • Pradip Das,
  • Nabadwip Sarkar

摘要

Inverse logarithmic coefficients play an important role in the theory of univalent functions. In this paper, we obtain sharp bounds for the inverse logarithmic coefficients associated with the class \(\mathcal {S}_e^*\) S e of starlike functions defined by the subordination condition \( \mathcal {S}_e^*:= \left\{ f \in \mathcal {S} : \frac{z f'(z)}{f(z)} \prec e^z,\; z \in \mathbb {D} \right\} . \) S e : = f S : z f ( z ) f ( z ) e z , z D . We further derive sharp estimates for the Hankel determinants constructed from these inverse logarithmic coefficients for functions in the class \(\mathcal {S}_e^*\) S e . In addition, we investigate the inverse logarithmic coefficient difference problem for this class. In each case, the obtained bounds are shown to be sharp, and the corresponding extremal functions are explicitly determined.