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Region of variability for functions with positive real part

Saminathan Ponnusamy, Allu Vasudevarao (2010)

Annales Polonici Mathematici

For γ ∈ ℂ such that |γ| < π/2 and 0 ≤ β < 1, let γ , β denote the class of all analytic functions P in the unit disk with P(0) = 1 and R e ( e i γ P ( z ) ) > β c o s γ in . For any fixed z₀ ∈ and λ ∈ ̅, we shall determine the region of variability V ( z , λ ) for 0 z P ( ζ ) d ζ when P ranges over the class ( λ ) = P γ , β : P ' ( 0 ) = 2 ( 1 - β ) λ e - i γ c o s γ . As a consequence, we present the region of variability for some subclasses of univalent functions. We also graphically illustrate the region of variability for several sets of parameters.

Region of variability for spiral-like functions with respect to a boundary point

S. Ponnusamy, A. Vasudevarao, M. Vuorinen (2009)

Colloquium Mathematicae

For μ ∈ ℂ such that Re μ > 0 let μ denote the class of all non-vanishing analytic functions f in the unit disk with f(0) = 1 and R e ( 2 π / μ z f ' ( z ) / f ( z ) + ( 1 + z ) / ( 1 - z ) ) > 0 in . For any fixed z₀ in the unit disk, a ∈ ℂ with |a| ≤ 1 and λ ∈ ̅, we shall determine the region of variability V(z₀,λ) for log f(z₀) when f ranges over the class μ ( λ ) = f μ : f ' ( 0 ) = ( μ / π ) ( λ - 1 ) a n d f ' ' ( 0 ) = ( μ / π ) ( a ( 1 - | λ | ² ) + ( μ / π ) ( λ - 1 ) ² - ( 1 - λ ² ) ) . In the final section we graphically illustrate the region of variability for several sets of parameters.

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