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.

scholarly journals Coefficient Problems in a Class of Functions with Bounded Turning Associated with Sine Function

2021 ◽  
Vol 14 (1) ◽  
pp. 53-64
Author(s):  
Muhammad Ghaffar Khan ◽  
Bakhtiar Ahmad ◽  
Janusz Sokol ◽  
Zubair Muhammad ◽  
Wali Khan Mashwani ◽  
...  
Keyword(s):  
Power Series ◽  
Univalent Functions ◽  
Upper Bounds ◽  
Sine Function ◽  
Hankel Determinant ◽  
Hankel Determinants ◽  
The Third ◽  
Coefficient Problems ◽  
Bounded Turning ◽  
Class Of Functions

The Hankel determinant for a function having power series was first defined by Pommerenke. The growth of Hankel determinant has been evaluated for different subcollections of univalent functions. Many subclasses with bounded turning are several interesting geometric properties. In this paper, some classes of functions with bounded turning which connect to the sine function are studied in the region of the unit disc in order. Our purpose is to obtain some upper bounds for the third and fourth Hankel determinants related to such classes.

scholarly journals Bounds on the Third Order Hankel Determinant for Certain Subclasses of Analytic Functions

2017 ◽  
Vol 25 (3) ◽  
pp. 199-214
Author(s):  
S.P. Vijayalakshmi ◽  
T.V. Sudharsan ◽  
Daniel Breaz ◽  
K.G. Subramanian
Keyword(s):  
Series Expansion ◽  
Taylor Series ◽  
Analytic Functions ◽  
Unit Disc ◽  
Taylor Series Expansion ◽  
Upper Bounds ◽  
Hankel Determinant ◽  
Third Order ◽  
The Third

Abstract Let A be the class of analytic functions f(z) in the unit disc ∆ = {z ∈ C : |z| < 1g with the Taylor series expansion about the origin given by f(z) = z+ ∑n=2∞ anzn, z ∈∆ : The focus of this paper is on deriving upper bounds for the third order Hankel determinant H3(1) for two new subclasses of A.

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

scholarly journals A note on successive coefficients of spirallike functions

Filomat ◽  
2018 ◽  
Vol 32 (4) ◽  
pp. 1199-1207 ◽  
Author(s):  
Ming Li
Keyword(s):  
Unit Disk ◽  
Univalent Functions ◽  
Starlike Functions ◽  
Upper Bounds ◽  
Extremal Functions ◽  
Lower And Upper Bounds ◽  
Bieberbach Conjecture ◽  
Precise Form ◽  
Spirallike Functions ◽  
Class Of Functions

Even there were several facts to show that ||an+1(f)|-|an(f)|| ? 1 is not true for the whole class of normalised univalent functions in the unit disk with with the form f(z) = z + ??,k=2 akzk. In 1978, Leung[7] proved ||an+1(f)|-|an(f)|| is actually bounded by 1 for starlike functions and by this result it is easy to get the conclusion |an| ? n for starlike functions. Since ||an+1(f)|-|an(f)|| ? 1 implies the Bieberbach conjecture (now the de Brange theorem), so it is still interesting to investigate the bound of ||an+1(f)|-|an(f)|| for the class of spirallike functions as this class of functions is closely related to starlike functions. In this article we prove that this functional is bounded by 1 and equality occurs only for the starlike case. We are also able to give a precise form of extremal functions. Furthermore we also try to find the sharp bound of ||an+1(f)|-|an(f)|| for non-starlike spirallike functions. By using the Carath?odory-Toeplitz theorem, we obtain the sharp lower and upper bounds of |an+1(f)|-|an(f)| for n = 1 and n = 2. These results disprove the expected inequality ||an+1(f)|-|an(f)||? cos ? for ?-spirallike functions.

Application of subordination for estimating the Hankel determinant for subclass of univalent functions

2021 ◽  
Vol 30 (1) ◽  
pp. 69-74
Author(s):  
SH. NAJAFZADEH ◽  
H. RAHMATAN ◽  
H. HAJI
Keyword(s):  
Convex Functions ◽  
Univalent Functions ◽  
Hankel Determinant ◽  
Hankel Determinants ◽  
The Third

By using subordination structure, a new subclass of convex functions is introduced. The estimate of the third Hankel determinants is also investigated.

scholarly journals Upper Bound of Second Hankel Determinant for Certain Subclasses of Analytic Functions

2014 ◽  
Vol 2014 ◽  
pp. 1-10 ◽  
Author(s):  
Ming-Sheng Liu ◽  
Jun-Feng Xu ◽  
Ming Yang
Keyword(s):  
Upper Bound ◽  
Analytic Functions ◽  
Univalent Functions ◽  
Upper Bounds ◽  
Hankel Determinant ◽  
Second Hankel Determinant ◽  
Work Done

In this present investigation, we first give a survey of the work done so far in this area of Hankel determinant for univalent functions. Then the upper bounds of the second Hankel determinant|a2a4−a32|for functions belonging to the subclassesS(α,β),K(α,β),Ss∗(α,β), andKs(α,β)of analytic functions are studied. Some of the results, presented in this paper, would extend the corresponding results of earlier authors.

scholarly journals Coefficient Problem for Certain Classes of Analytic Functions using Hankel Determinant

2019 ◽  
Vol 8 (10S) ◽  
pp. 301-307
Keyword(s):  
Analytic Functions ◽  
Unit Disc ◽  
Univalent Functions ◽  
Upper Bounds ◽  
Hankel Determinant ◽  
Coefficient Problem

In this paper, we introduce some classes of analytic-univalent functions and for any real µ, determine the sharp upper bounds of the functional for the functions of the form k=2 belonging to such classes in the unit disc E = {z : |z| <1}

SHARP BOUNDS OF SOME COEFFICIENT FUNCTIONALS OVER THE CLASS OF FUNCTIONS CONVEX IN THE DIRECTION OF THE IMAGINARY AXIS

2019 ◽  
Vol 100 (1) ◽  
pp. 86-96 ◽  
Author(s):  
NAK EUN CHO ◽  
BOGUMIŁA KOWALCZYK ◽  
ADAM LECKO
Keyword(s):  
Analytic Functions ◽  
Imaginary Axis ◽  
Schwarz Lemma ◽  
Hankel Determinant ◽  
Sharp Estimates ◽  
The Third ◽  
Carathéodory Functions ◽  
Unit Polydisk ◽  
Class Of Functions ◽  
The Schwarz Lemma

We apply the Schwarz lemma to find general formulas for the third coefficient of Carathéodory functions dependent on a parameter in the closed unit polydisk. Next we find sharp estimates of the Hankel determinant $H_{2,2}$ and Zalcman functional $J_{2,3}$ over the class ${\mathcal{C}}{\mathcal{V}}$ of analytic functions $f$ normalised such that $\text{Re}\{(1-z^{2})f^{\prime }(z)\}>0$ for $z\in \mathbb{D}:=\{z\in \mathbb{C}:|z|<1\}$, that is, the subclass of the class of functions convex in the direction of the imaginary axis.

scholarly journals Second Hankel Determinants for the Class of Typically Real Functions

2016 ◽  
Vol 2016 ◽  
pp. 1-7 ◽  
Author(s):  
Paweł Zaprawa
Keyword(s):  
Unit Disk ◽  
Lower Bounds ◽  
Analytic Functions ◽  
Upper And Lower Bounds ◽  
Hankel Determinants ◽  
Real Functions ◽  
Typically Real ◽  
Typically Real Functions

We discuss the Hankel determinantsH2(n)=anan+2-an+12for typically real functions, that is, analytic functions which satisfy the conditionIm ⁡z Im⁡f(z)≥0in the unit disk Δ. Main results are concerned withH2(2)andH2(3). The sharp upper and lower bounds are given. In general case, forn≥4, the results are not sharp. Moreover, we present some remarks connected with typically real odd functions.

Coefficient inequalities related with typically real functions

2020 ◽  
Vol 70 (4) ◽  
pp. 829-838
Author(s):  
Saqib Hussain ◽  
Shahid Khan ◽  
Khalida Inayat Noor ◽  
Mohsan Raza
Keyword(s):  
Unit Disk ◽  
Real Functions ◽  
Coefficient Inequalities ◽  
Typically Real ◽  
Class Of Functions ◽  
Typically Real Functions

AbstractIn this paper, we are mainly interested to study the generalization of typically real functions in the unit disk. We study some coefficient inequalities concerning this class of functions. In particular, we find the Zalcman conjecture for generalized typically real functions.

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