<p>Recently, the Wang et al. [<CitationRef CitationID="CR15">15</CitationRef>] proposed a coefficient conjecture for the family <InlineEquation ID="IEq1"> <EquationSource Format="TEX">\(\mathcal {S}_H^0(K)\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <msubsup> <mi mathvariant="script">S</mi> <mi>H</mi> <mn>0</mn> </msubsup> <mrow> <mo stretchy="false">(</mo> <mi>K</mi> <mo stretchy="false">)</mo> </mrow> </mrow> </math></EquationSource> </InlineEquation> of <i>K</i>-quasiconformal harmonic mappings <InlineEquation ID="IEq2"> <EquationSource Format="TEX">\(f = h + \overline{g}\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>f</mi> <mo>=</mo> <mi>h</mi> <mo>+</mo> <mover> <mi>g</mi> <mo>¯</mo> </mover> </mrow> </math></EquationSource> </InlineEquation> that are sense-preserving and univalent, where <InlineEquation ID="IEq3"> <EquationSource Format="TEX">\(h(z)=z+\sum _{k=2}^{\infty }a_kz^k\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>h</mi> <mrow> <mo stretchy="false">(</mo> <mi>z</mi> <mo stretchy="false">)</mo> </mrow> <mo>=</mo> <mi>z</mi> <mo>+</mo> <msubsup> <mo>∑</mo> <mrow> <mi>k</mi> <mo>=</mo> <mn>2</mn> </mrow> <mi>∞</mi> </msubsup> <msub> <mi>a</mi> <mi>k</mi> </msub> <msup> <mi>z</mi> <mi>k</mi> </msup> </mrow> </math></EquationSource> </InlineEquation> and <InlineEquation ID="IEq4"> <EquationSource Format="TEX">\(g(z)=\sum _{k=1}^{\infty }b_kz^k\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>g</mi> <mrow> <mo stretchy="false">(</mo> <mi>z</mi> <mo stretchy="false">)</mo> </mrow> <mo>=</mo> <msubsup> <mo>∑</mo> <mrow> <mi>k</mi> <mo>=</mo> <mn>1</mn> </mrow> <mi>∞</mi> </msubsup> <msub> <mi>b</mi> <mi>k</mi> </msub> <msup> <mi>z</mi> <mi>k</mi> </msup> </mrow> </math></EquationSource> </InlineEquation> are analytic in the unit disk <InlineEquation ID="IEq5"> <EquationSource Format="TEX">\(|z|&lt;1\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mo stretchy="false">|</mo> <mi>z</mi> <mo stretchy="false">|</mo> <mo>&lt;</mo> <mn>1</mn> </mrow> </math></EquationSource> </InlineEquation>, and the dilatation <InlineEquation ID="IEq6"> <EquationSource Format="TEX">\(\omega =g'/h'\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>ω</mi> <mo>=</mo> <msup> <mi>g</mi> <mo>′</mo> </msup> <mo stretchy="false">/</mo> <msup> <mi>h</mi> <mo>′</mo> </msup> </mrow> </math></EquationSource> </InlineEquation> satisfies the condition <InlineEquation ID="IEq7"> <EquationSource Format="TEX">\(|\omega (z)| \le k&lt;1\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mo stretchy="false">|</mo> <mi>ω</mi> <mo stretchy="false">(</mo> <mi>z</mi> <mo stretchy="false">)</mo> <mo stretchy="false">|</mo> <mo>≤</mo> <mi>k</mi> <mo>&lt;</mo> <mn>1</mn> </mrow> </math></EquationSource> </InlineEquation> for <InlineEquation ID="IEq8"> <EquationSource Format="TEX">\({\mathbb D}\)</EquationSource> <EquationSource Format="MATHML"><math> <mi mathvariant="double-struck">D</mi> </math></EquationSource> </InlineEquation>, with <InlineEquation ID="IEq9"> <EquationSource Format="TEX">\(K=\frac{1+k}{1-k}\ge 1\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mi>K</mi> <mo>=</mo> <mfrac> <mrow> <mn>1</mn> <mo>+</mo> <mi>k</mi> </mrow> <mrow> <mn>1</mn> <mo>-</mo> <mi>k</mi> </mrow> </mfrac> <mo>≥</mo> <mn>1</mn> </mrow> </math></EquationSource> </InlineEquation>. The main aim of this article is to provide an affirmative answer in support of this conjecture by proving this conjecture for every starlike function (resp. close-to-convex function) from <InlineEquation ID="IEq10"> <EquationSource Format="TEX">\(\mathcal {S}^0_H(K)\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <msubsup> <mrow> <mi mathvariant="script">S</mi> </mrow> <mi>H</mi> <mn>0</mn> </msubsup> <mrow> <mo stretchy="false">(</mo> <mi>K</mi> <mo stretchy="false">)</mo> </mrow> </mrow> </math></EquationSource> </InlineEquation>. In addition, we verify this conjecture also for typically real <i>K</i>-quasiconformal harmonic mappings. Also, we establish sharp coefficients estimate of convex <i>K</i>-quasiconformal harmonic mappings. By doing so, our work provides a document in support of the main conjecture of Wang et al..</p>

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On the coefficients estimate of K-quasiconformal harmonic mappings

  • Peijin Li,
  • Saminathan Ponnusamy

摘要

Recently, the Wang et al. [15] proposed a coefficient conjecture for the family \(\mathcal {S}_H^0(K)\) S H 0 ( K ) of K-quasiconformal harmonic mappings \(f = h + \overline{g}\) f = h + g ¯ that are sense-preserving and univalent, where \(h(z)=z+\sum _{k=2}^{\infty }a_kz^k\) h ( z ) = z + k = 2 a k z k and \(g(z)=\sum _{k=1}^{\infty }b_kz^k\) g ( z ) = k = 1 b k z k are analytic in the unit disk \(|z|<1\) | z | < 1 , and the dilatation \(\omega =g'/h'\) ω = g / h satisfies the condition \(|\omega (z)| \le k<1\) | ω ( z ) | k < 1 for \({\mathbb D}\) D , with \(K=\frac{1+k}{1-k}\ge 1\) K = 1 + k 1 - k 1 . The main aim of this article is to provide an affirmative answer in support of this conjecture by proving this conjecture for every starlike function (resp. close-to-convex function) from \(\mathcal {S}^0_H(K)\) S H 0 ( K ) . In addition, we verify this conjecture also for typically real K-quasiconformal harmonic mappings. Also, we establish sharp coefficients estimate of convex K-quasiconformal harmonic mappings. By doing so, our work provides a document in support of the main conjecture of Wang et al..