scholarly journals Certain classes of univalent functions with negative coefficients II

1976 ◽  
Vol 15 (3) ◽  
pp. 467-473 ◽  
Author(s):  
V.P. Gupta ◽  
P.K. Jain
Keyword(s):  
Univalent Functions ◽  
Arithmetic Mean ◽  
Distortion Theorem ◽  
Linear Combinations ◽  
Radius Of Convexity ◽  
Image Position ◽  
Class Of Functions

Let P*(α, β) denote the class of functionsanalytic and univalent in |z| < 1 for whichwhere α є [0, 1), β є (0, 1].Sharp results concerning coefficients, distortion theorem and radius of convexity for the class P*(α, β) are determined. A comparable theorem for the classes C*(α, β) and P*(α, β) is also obtained. Furthermore, it is shown that the class P*(α, ß) is closed under ‘arithmetic mean’ and ‘convex linear combinations’.

scholarly journals K-Fold symmetric starlike univalent functions

1985 ◽  
Vol 32 (3) ◽  
pp. 419-436 ◽  
Author(s):  
V. V. Anh
Keyword(s):  
Unit Disc ◽  
Univalent Functions ◽  
Coefficient Bounds ◽  
Radius Of Convexity ◽  
Covering Theorems ◽  
Image Position

This paper establishes the radius of convexity, distortion and covering theorems for the classwhere−1 ≤ B < A ≤ 1, w(0) = 0, |w (z)| < 1 in the unit disc. Coefficient bounds for functions in are also derived.

scholarly journals Univalent functions with univalent Gelfond-Leontev derivatives

1984 ◽  
Vol 29 (3) ◽  
pp. 329-348 ◽  
Author(s):  
O.P. Juneja ◽  
S.M. Shah
Keyword(s):  
Unit Disk ◽  
Shift Operator ◽  
Univalent Functions ◽  
Nondecreasing Sequence ◽  
Growth Properties ◽  
Linear Invariant ◽  
Definition Of ◽  
Image Position ◽  
Linear Invariant Family ◽  
Class Of Functions

Let be a nondecreasing sequence of positive numbers. We consider Gelfond-Leontev derivative Df(z), of a function , defined by for univalence and growth properties, and extend some results of Shah and Trimble. Set en = {d1d2 … dn), n≥l, e0 = 1, . Let r be the radius of convergence of p(z). We state parts of Theorem 1 and Corollaries. Let f and all Dkf, k = 1, 2,…, be analytic and univalent in the unit disk U. Then(iii) if p is entire and of growth (ρ, T) then f must be entire and of growth not exceeding (ρ, 2d2T),(iv) if D corresponds to the shift operator (dn ≡ l), then .Another class of functions is defined by a condition of the form |an+1/an| ≤ bn+1/dn+1, where is a sequence of positive numbers satisfying and inequality, and it is shown that all functions in this class along with all their Gelfond–Leontev successive derivatives are regular and univalent in U. An extension of the definition of a linear invariant family is given and results analogous to (i) and (ii) are stated.

scholarly journals Meromorphic starlike univalent functions

1984 ◽  
Vol 30 (3) ◽  
pp. 395-410 ◽  
Author(s):  
V. V. Anh ◽  
P. D. Tuan
Keyword(s):  
Univalent Functions ◽  
Upper Bounds ◽  
Lower And Upper Bounds ◽  
Geometric Properties ◽  
Image Position ◽  
Class Of Functions

Let B be the class of functions ω(z) regular in |z| < 1 and satisfying ω(0) = 0, |ω(z)|<1 in |z|<1. We denote by P(A, B), −1 ≤ B < A ≤1, the class of functions p(z) = l+p1z+… regular in |z| < 1 and such that p(z) = [1+Aω(z)]/[1+Bω(z)] for some ω(z) ∈ Β. This paper establishes sharp lower and upper bounds on |z| = r<1 for the functionalwhere p(z) varies in P(A, B). The results are then used to study certain geometric properties of the corresponding class of meromorphic starlike univalent functions

Linear Combinations of Univalent Functions with Complex Coefficients

1971 ◽  
Vol 23 (4) ◽  
pp. 712-717 ◽  
Author(s):  
Robert K. Stump
Keyword(s):  
Linear Combination ◽  
Convex Domain ◽  
Analytic Functions ◽  
Univalent Functions ◽  
Linear Combinations ◽  
Radius Of Starlikeness ◽  
Complex Constant ◽  
Complex Functions ◽  
Image Position ◽  
Complex Coefficients

Let U be the class of all normalized analytic functionswhere z ∈ E = {z : |z| < 1} and ƒ is univalent in E. Let K denote the sub-class of U consisting of those members that map E onto a convex domain. MacGregor [2] showed that if ƒ1 ∈ K and ƒ2 ∈ K and if1then F ∉ K when λ is real and 0 < λ < 1, and the radius of univalency and starlikeness for F is .In this paper, we examine the expression (1) when ƒ1 ∈ K, ƒ2 ∈ K and λ is a complex constant and find the radius of starlikeness for such a linear combination of complex functions with complex coefficients.

scholarly journals Certain classes of univalent functions with negative coefficients

1976 ◽  
Vol 14 (3) ◽  
pp. 409-416 ◽  
Author(s):  
V.P. Gupta ◽  
P.K. Jain
Keyword(s):  
Univalent Functions ◽  
Representation Formula ◽  
Arithmetic Mean ◽  
Linear Combinations ◽  
Analytic And Univalent Functions

The subclasses S*(α, β) and C*(α, β) of T, the class of analytic and univalent functions of the form have been considered. Sharp results concerning coefficients, distortion of functions belonging to S*(α, β) and C*(α, β) are determined along with a representation formula for the functions in S*(α, β). Furthermore, it is shown that the classes S*(α, β) and C*(α,.β) are closed under arithmetic mean and convex linear combinations.

scholarly journals On the radii of starlikeness and convexity of certain classes of regular functions

1972 ◽  
Vol 13 (2) ◽  
pp. 208-218
Author(s):  
Pran Nath Chichra
Keyword(s):  
Positive Root ◽  
Open Disc ◽  
Regular Functions ◽  
Radius Of Convexity ◽  
Image Position ◽  
Class Of Functions ◽  
Radius Of Univalence

Let Rn denote the class of functions f(z) = z+anzn+ … (n ≧ 2) which are regular in the open disc|z| < 1 (hereafter called E) and satisfy for all z in E. Rnis a subclass of the class of close-to-star function in E [9, p. 61]. MacGregor showed that the radius of univalence and starlikeness of Rn is , see [4,5]. The radius of convexity of R = R2 is r0 = 0.179 …, where r0 is the smallest positive root of the equation 1−5r−3r2−r3 = 0, see [8].

Means and coefficients of functions which omit a sequence of values

1977 ◽  
Vol 81 (1) ◽  
pp. 47-57
Author(s):  
Albert Baernstein ◽  
Richard Rochberg
Keyword(s):  
Unit Disk ◽  
Univalent Functions ◽  
Maximum Modulus ◽  
Distortion Theorem ◽  
Principle Of Subordination ◽  
Image Position ◽  
Simply Connected

Suppose that f is analytic in the unit disk D. If its range f(D) is contained in a simply connected proper subdomain of the plane, then the principle of subordination and the distortion theorem for univalent functions show thatwhere M(r, f) denotes the maximum modulus of f. Cartwright (2) studied functions which, instead of omitting all values on a continuum stretching to infinity, omit only a sequence of values. She assumed that the sequence {wn} satisfiesandand proved that if f(D) contains none of the points {wn} thenmfor every ε > 0. Cartwright's proof was based on the Ahlfors Distortion Theorem, and is quite complicated. A much simpler proof was given by Pommerenke in (10). The key idea in his proof will also be used in the present paper.

A Class of Harmonic Starlike Functions defined by Multiplier Transformation

2020 ◽  
pp. 455-469
Author(s):  
Deepali Khurana ◽  
Raj Kumar ◽  
Sibel Yalcin
Keyword(s):  
Convex Combination ◽  
Univalent Functions ◽  
Extreme Points ◽  
Starlike Functions ◽  
Harmonic Mappings ◽  
Distortion Bounds ◽  
Radius Of Convexity ◽  
Univalent Harmonic Mappings ◽  
Harmonic Starlike ◽  
Multiplier Transformation

We define two new subclasses, $HS(k, \lambda, b, \alpha)$ and \linebreak $\overline{HS}(k, \lambda, b, \alpha)$, of univalent harmonic mappings using multiplier transformation. We obtain a sufficient condition for harmonic univalent functions to be in $HS(k,\lambda,b,\alpha)$ and we prove that this condition is also necessary for the functions in the class $\overline{HS} (k,\lambda,b,\alpha)$. We also obtain extreme points, distortion bounds, convex combination, radius of convexity and Bernandi-Libera-Livingston integral for the functions in the class $\overline{HS}(k,\lambda,b,\alpha)$.

Radius problems for univalent functions

2020 ◽  
Vol 26 (1) ◽  
pp. 111-115
Author(s):  
Janusz Sokół ◽  
Katarzyna Trabka-Wiȩcław
Keyword(s):  
Unit Disk ◽  
Univalent Functions ◽  
Radius Problems ◽  
Radius Of Convexity

AbstractThis paper considers the following problem: for what value r, {r<1} a function that is univalent in the unit disk {|z|<1} and convex in the disk {|z|<r} becomes starlike in {|z|<1}. The number r is called the radius of convexity sufficient for starlikeness in the class of univalent functions. Several related problems are also considered.

Third Hankel determinants for two classes of analytic functions with real coefficients

2021 ◽  
Vol 33 (4) ◽  
pp. 973-986
Author(s):  
Young Jae Sim ◽  
Paweł Zaprawa
Keyword(s):  
Analytic Functions ◽  
Univalent Functions ◽  
Upper Bounds ◽  
Hankel Determinant ◽  
Lower And Upper Bounds ◽  
Hankel Determinants ◽  
The Third ◽  
Typically Real ◽  
Class Of Functions ◽  
Typically Real Functions

Abstract In recent years, the problem of estimating Hankel determinants has attracted the attention of many mathematicians. Their research have been focused mainly on deriving the bounds of H 2 , 2 {H_{2,2}} or H 3 , 1 {H_{3,1}} over different subclasses of 𝒮 {\mathcal{S}} . Only in a few papers third Hankel determinants for non-univalent functions were considered. In this paper, we consider two classes of analytic functions with real coefficients. The first one is the class 𝒯 {\mathcal{T}} of typically real functions. The second object of our interest is 𝒦 ℝ ⁢ ( i ) {\mathcal{K}_{\mathbb{R}}(i)} , the class of functions with real coefficients which are convex in the direction of the imaginary axis. In both classes, we find lower and upper bounds of the third Hankel determinant. The results are sharp.

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