Научная статья на тему 'Hankel determinant of third kind for Certain subclass of multivalent analytic functions'

Hankel determinant of third kind for Certain subclass of multivalent analytic functions Текст научной статьи по специальности «Математика»

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P-VALENT ANALYTIC FUNCTION / UPPER BOUND / THIRD HANKEL DETERMINANT / POSITIVE REAL FUNCTION

Аннотация научной статьи по математике, автор научной работы — Vamshee Krishna D., Shalini D.

The objective of this paper is to obtain an upper bound (not sharp) to the third order Hankel determinant for certain subclass of multivalent (p-valent) analytic functions, defined in the open unit disc E. Using the Toeplitz determinants, we may estimate the Hankel determinant of third kind for the normalized multivalent analytic functions belongng to this subclass. But, using the technique adopted by Zaprawa [1], i.e., grouping the suitable terms in order to apply Lemmas due to Hayami [2], Livingston [3] and Pommerenke [4], we observe that, the bound estimated by the method adopted by Zaprawa is more refined than using upon applying the Toeplitz determinants.

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ОПРЕДЕЛИТЕЛЬ ГАНКЕЛЯ ТРЕТЬЕГО РОДА ДЛЯ НЕКОТОРОГО ПОДКЛАССА МНОГОВАЛЕНТНЫХ АНАЛИТИЧЕСКИХ ФУНКЦИЙ

Целью данной статьи является получение (не точной) верхней границы для определителя Ганкеля третьего порядка для некоторого подкласса многовалентных (p-валентных) аналитических функций, определенных на открытом единичном диске E. Используя определители Теплица, мы можем оценить определитель Ганкеля третьего рода для нормированных многовалентных аналитических функций, принадлежащих этому подклассу. Однако, используя технику, принятую Саправой [1], т. е. группируя подходящие члены для применения лемм Хаями [2], Ливингстона [3] и Померенке [4], мы видим, что оценка методом Саправы точнее, чем при применении определителей Теплица.

Текст научной работы на тему «Hankel determinant of third kind for Certain subclass of multivalent analytic functions»

Vladikavkaz Mathematical Journal 2020, Volume 22, Issue 1, P. 43-48

YAK 512.643.86+517.546 DOI 10.23671/VNC.2020.1.57538

HANKEL DETERMINANT OF THIRD KIND FOR CERTAIN SUBCLASS OF MULTIVALENT ANALYTIC FUNCTIONS

D. Vamshee Krishna1 and D. Shalini2

1 GITAM Institute of Science, Visakhapatnam 530045, Andhra Pradesh, India; 2 Dr. B. R. Ambedkar University, Srikakulam 532410, Andhra Pradesh, India E-mail: vamsheekrishna1972@gmail.com, shaliniraj1005@gmail.com

Abstract. The objective of this paper is to obtain an upper bound (not sharp) to the third order Hankel determinant for certain subclass of multivalent (p-valent) analytic functions, defined in the open unit disc E. Using the Toeplitz determinants, we may estimate the Hankel determinant of third kind for the normalized multivalent analytic functions belongng to this subclass. But, using the technique adopted by Zaprawa [1], i. e., grouping the suitable terms in order to apply Lemmas due to Hayami [2], Livingston [3] and Pommerenke [4], we observe that, the bound estimated by the method adopted by Zaprawa is more refined than using upon applying the Toeplitz determinants.

Key words: p-valent analytic function, upper bound, third Hankel determinant, positive real function. Mathematical Subject Classification (2010): 30C45, 30C50.

For citation: Vamshee Krishna, D. and Shalini, D. Hankel Determinant of Third Kind for Certain Subclass of Multivalent Analytic Functions, Vladikavkaz Math. J., 2019, vol. 21, no. 3, pp. 43-48. DOI: 10.23671/VNC.2020.1.57538.

1. Introduction

Let Ap (p is a fixed integer ^ 1) denotes the class of functions f of the form

f (z) = zpJ2 ap+nzn

(1.1)

n=0

in the open unit disc E = {z : |z| < 1} with p e N = {1,2,3,...}. Let S be the subclass of A\ = A, consisting of univalent functions. In 1985, Louis de Branges de Bourcia proved the Bieberbach conjecture also called as Coefficient conjecture, which states that for a univalent function its nth-Taylor's coefficient is bounded by n (see [5]). The bounds for the coefficients of these functions give information about their geometric properties. In particular, the growth and distortion properties of a normalized univalent function are determined by the bound of its second coefficient. The Hankel determinant of f given in (1.1) (when p = 1), for q,n e N was defined by Pommerenke [6] as follows and has been extensively studied by many authors:

(1.2)

(in an+1 ' O-ra+ç— 1

Hq{n) = öra+l an+2 ' O-ra+ç

an+q-1 an+q ' dn+2q-2

© 2020 Vamshee Krishna, D. and Shalini, D.

One can easily observe that the Fekete-Szego functional is H2(1). In recent years, the research on Hankel determinants has focused on the estimation of |H2(2)|, where

H2(2) =

a2

0>3 (I4

(12U4

known as the second Hankel determinant obtained for q = 2 and n = 2 in (1.2). Many authors obtained upper bound to the functional |a2a4 — a31 for various subclasses of univalent and multivalent analytic functions. The exact (sharp) estimates of |H2(2)| for the subclasses of S namely, bounded turning, starlike and convex functions denoted by R, S* and K respectively in the open unit disc E, that is, functions satisfying the conditions Re f '(z) > 0, Re |Zf(z) } > 0 and Re |l + } > 0 were proved by Janteng et al. [7, 8] and obtained the bounds as 4/9, 1, and 1/8 respectively. For the class S*(^) of Ma-Minda starlike functions, the exact bound of the second Hankel determinant was obtained by Lee et al. [9]. Choosing q = 2 and n = p + 1 in (1.2), we obtain the second Hankel determinant for the p-valent function (see [10]), namely

H2(p + 1) =

ap+1 ap+2 ap+2 ap+3

ap+1ap+3 — ap+2-

The case q = 3 appears to be much more difficult than the case q = 2. Very few papers have been devoted to the third Hankel determinant denoted by H3(1), obtained by choosing q = 3 and n = 1 in (1.2). Babalola [11] is the first one, who tried to estimate an upper bound to |H3(1)| for the classes R, S* and K. Following this paper, Raza and Malik [12] obtained an upper bound for the third Hankel determinant for a class of analytic functions related with lemniscate of Bernoulli. Sudharsan et al. [13] derived an upper bound to H3(1) for a subclass of analytic functions. Bansal et al. [14] modified the upper bound for |H3(1)| for some of the classes estimated by Babalola [11] to some extent. Recently, Zaprawa [1] improved the results obtained by Babalola [11]. Further, Orhan and Zaprawa [15] obtained an upper bound for third Hankel determinant for the classes S* and K functions of order alpha. Very recently, Kowalczyk et al. [16] estimated sharp upper bound to |H3(1)| for the class of convex functions Jf and showed as |ii3(l)| ^ j^, which is far better than the bound obtained by Zaprawa [1]. Lecko et al. [17] calculated sharp bound for Hankel determinant of the third kind for starlike functions of order 1/2. For our discussion in this paper, we consider H3(p) for the values q = 3 and n = p in (1.2), called as Hankel determinant of third order for the p-valent function given in (1.1), namely

H3(p) =

ap ap+1 ap+2 ap+1 ap+2 ap+3 ap+2 ap+3 ap+4

((p = 1).

Expanding the determinant, we have

H3(p) = [ap(ap+2(p+4 — ap+3)

equivalently

+ (p+1 (ap+2ap+3 — ap+1(p+4) + ap+2(ap+1(p+3 — ap+2 )], (1.3)

H3(p) = H2 (p + 2) + flp+1 Jp+1 + (p+2H2(p + 1),

where Jp+1 = (ap+2ap+3 — ap+1ap+4) and H2(p + 2) = (ap+2ap+4 — a^).

Motivated by the results obtained by different authors mentioned above and who are working in this direction (see [18, 19]), in particular the result obtained by Zaprawa [1] in finding an upper bound to the Hankel determinant of third kind for the subclass R of S, consisting of functions whose derivative has a positive real part (also called as bounded turning functions), introduced by Alexander in 1915 and a systematic study of properties of these functions was conducted by MacGregor [20], who indeed referred to numerous earlier investigations involving functions whose derivative has a positive real part. In the present paper, we are making an attempt to obtain an upper bound to |H3(p)|, for the function f given in (1.1), when it belongs to certain subclass of analytic functions, defined as follows.

Definition 1.1. A function f e Ap is said to be in the class Ip(ft) (ft is real) (see [21]), if it satisfies the condition

¿€£-{0}. (1.4)

1. Choosing ft = 1 and p = 1, we obtain I1(1) = R.

2. Selecting ft = 1, we get Ip(1) = Rp, denotes the class of multivalent bounded turning functions.

In proving our result, we require a few sharp estimates in the form of Lemmas valid for functions with positive real part.

Let P denote the class of functions consisting of g, such that

<x

g(z) = 1 + ciz + C2Z2 + C3Z3 + ... = 1 + Y^ CnZn, (1.5)

n=1

which are analytic in E and Reg(z) > 0 for z e E. Here g is called the Caratheodory function [22].

Lemma 1.1 [2]. If g e P, then the sharp estimate |ck — ¡ckcn-k| ^ 2, holds for n,k e N, with n > k and i e [0,1].

Lemma 1.2 [3]. If g e P, then the sharp estimate |ck — ckcn-k| ^ 2, holds for n,k e N, where n > k.

Lemma 1.3 [4]. If g e P then |c^ | ^ 2, for each k ^ 1 and the inequality is sharp for the function g(z) = j^, z £ E.

In order to obtain our result, we referred to the classical method devised by Libera and Zlotkiewicz [23, 24], used by several authors in the literature.

2. Main Result

Theorem 2.1. If f e Ip(ß) (ß ^ 1 is real ) with p € N, then

"4p2(6p6 + 60p5ß + 227p4ß2 + 426p3ß3 + 437p2 ß4 + 252pß5 + 68ß6)

|H3(p)| <

(p + ß)2(p + 2ß)3 (p + 3ß)2(p + 4ß)

< For the function f(z) = zp + anzn e Ip(ft), by virtue of Definition 1.1, there

exists an analytic function g e P in the open unit disc E with g(0) = 1 and Re g(z) > 0 such that

(1 - + ft^Q = g(z) & [(1 - I3)pf(z) + Pf'(z) = pzpg(z)]. (2.1)

pzp

Replacing f' and g with their series expressions in (2.1), upon simplification, we obtain

pC™ RJ

aP+n = —;—q, n,pG N. p + np

(2.2)

Substituting the values of ap+1, ap+2, ap+3 and ap+4 from (2.2) in the functional given in (1.3), it simplifies to

|H3(p)| = p2

C2C4

3

pc2

c2

c3

(p + 2P)(p + 4P) (p + 2P)3 (p + 3P)2

2

pcfc4

+

2pC1C2C3

(p + p)2(p + 4P) (p + p)(p + 2P)(p + 3P) On grouping the terms in (2.3), in order to apply Lemmas, we have

(2.3)

|H3(p)1 = p2

pC4(C2 — C2)

_(p + P)2(p + 4P) (p + 3P)2

C3 C3 —

6pC1C2

(p + P)(p + 2P)

1

+

pc2(c4 - c|) _ 2p2c2(c4 - C1C3) (p + 2/?)3 (p + /?)(p + 2/?)(p + 3/?)2

+

(p6 + 6p5p + 3p4p2 — 30p3p3 — 36p2p4 + 24pP5 + 36P6)C2C4

(p + P)2(p + 2P)3(p + 3P)2(p + 4P) Applying the triangle inequality in (2.4), we obtain

|H3(p)| < p2

+

1

p|c4||c2 - c\ I (p + /?)2(p + 4/?) ' (p + 3/?)2

|C3|

C3 —

6pC1C2

(p + P)(p + 2P)

p\c2\\c4~4\

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~r / /">\ Q i-

2p21C21| C4 — C1C3|

+

(p + 2P)3 (p + p)(p + 2P)(p + 3P)2

(p6 + 6P5f3 + 3p4/?2 - 30p3/?3 - 36p2/?4 + 24p(35 + 36/?6)|c2||c4| (p + /?)2(p + 2/?)3(p + 3/?)2(p + 4/?)

H3(p)

< 4p2

p

(p + P)2(p + 4P) 1

+

+

p

+

2p2

(p + 3P)2 (p + 2P)3 (p + P)(p + 2P)(p + 3P)2

+

(p + dp (3 + 3p /? - 30p3/?3 - 36p /? + 2Ap/3 + 36/?b)c2c4 (p + /?)2(p + 2/?)3(p + 3/?)2(p + 4/?)

Further simplification, we obtain

I" 4p2 (6p6 + 60p5f3 + 227p4/?2 + 426p3/?3 + 437p2/?4 + 252p/?5 + 68 f36) 1 3(P)I ^ [ (p + /?)2(p + 2/?)3(p + 3/?)2(p + 4/?)

This completes the proof of our Theorem. >

(2.4)

(2.5)

Upon using the Lemmas given in 1.2, 1.3 and 1.4 in the inequality (2.5), it reduces to

(2.6)

(2.7)

Remark 2.1. Choosing p = 1 and ft = 1 in the inequality (2.7), it coincides with the result obtained by Zaprawa [1].

Acknowledgement. The authors are extremely grateful to the esteemed Reviewers for a careful reading of the manuscript and making valuable suggestions leading to a better presentation of the paper.

References

1. Zaprawa, P. Third Hankel Determinants for Subclasses of Univalent Functions, Mediterranean Journal of Mathematics, 2017, vol. 14, no. 1, article 19. DOI: 10.1007/s00009-016-0829-y.

2. Hayami, T. and Owa, S. Generalized Hankel Determinant for Certain Classes, International Journal of Mathematical Analysis, 2010, vol. 4, no. 52, pp. 2573-2585.

3. Livingston, A. E. The Coefficients of Multivalent Close-to-Convex Functions, Proceedings of the American Mathematical Society, 1969, vol. 21, no. 3, pp. 545-552.

4. Pommerenke, Ch. Univalent Functions, Gottingen, Vandenhoeck and Ruprecht, 1975.

5. De Branges de Bourcia Louis. A Proof of Bieberbach Conjecture, Acta Math., 1985, vol. 154, no. 1-2, pp. 137-152.

6. Pommerenke, Ch. On the Coefficients and Hankel Determinants of Univalent Functions, Journal of the London Mathematical ¡Society, 1966, vol. 41 (s-1), pp. 111-122.

7. Janteng, A., Halim, S. A. and Darus, M. Hankel Determinant for Starlike and Convex Functions, International Journal of Mathematical Analysis, 2007, vol. 1, no. 13, pp. 619-625.

8. Janteng, A., Halim S. A. and Darus M. Coefficient Inequality for a Function Whose Derivative has a Positive Real Part, Journal of Inequalities in Pure and Applied Mathematics, vol. 7, no. 2, article 50.

9. Lee, S. K., Ravichandran, V. and Supramaniam, S. Bounds for the Second Hankel Determinant of Certain Univalent Functions, Journal of Inequalities and Applications, 2013, article 281. DOI: 10.1186/1029-242X-2013-281.

10. Vamshee Krishna, D. Coefficient Inequality for Certain p-Valent Analytic Functions, Rocky Mountain Journal of Mathematics, 2014, vol. 44, no. 6, pp. 1941-1959.

11. Babalola, K. O. On H3( 1) Hankel Determinant for Some Classes of Univalent Functions, Inequality Theory and Applications / ed. Y. J. Cho, J. K. Kim, S. S. Dragomir, New York, Nova Science Publishers, 2010, vol. 6, pp. 1-7.

12. Raza, M. and Malik, S. N. Upper Bound of Third Hankel Determinant for a Class of Analytic Functions Related with Lemniscate of Bernoulli, Journal of Inequalities and Applications, 2013, article 412. DOI: 10.1186/1029-242X-2013-412.

13. Sudharsan, T. V., Vijayalakshmi, S. P. and Stephen, B. A. Third Hankel Determinant for a Subclass of Analytic Functions, Malaya Journal of Matematik, 2014, vol. 2, no. 4, pp. 438-444.

14. Bansal, D, Maharana, S. and Prajapat, J. K. Third Order Hankel Determinant for Certain Univalent Functions, Journal of the Korean Mathematical Society, 2015, vol. 52, no. 6, pp. 1139-1148.

15. Orhan, H. and Zaprawa, P. Third Hankel Determinants for Starloke and Convex Funxtions of Order Alpha, Bulletin of the Korean Mathematical Society, 2018, vol. 55, no. 1, pp. 165-173.

16. Kowalczyk, B., Lecko, A. and Sim, Y. J. The Sharp Bound for the Hankel Determinant of the Third Kind for Convex Functions, Bulletin of the Australian Mathematical Society, 2018, vol. 97, no. 3, pp. 435-445. DOI: 10.1017/S0004972717001125.

17. Lecko, A., Sim, Y. J. and Smiarowska, B. The Sharp Bound of the Hankel Determinant of the Third Kind for Starlike Functions of Order 1/2, Complex Analysis and Operator Theory, 2019, vol. 13, no. 5, pp. 2231-2238. DOI: 10.1007/s11785-018-0819-0.

18. Cho, N. E., Kowalczyk B., Kwon, O. S. at al. The Bounds of Some Determinants for Starlike Functions of Order Alpha, Bulletin of the Malaysian Mathematical Sciences Society, 2018, vol. 41, no. 1, pp. 523-535. DOI: 10.1007/s40840-017-0476-x.

19. Vamshee Krishna, D. and Shalini, D. Bound on H3( 1) Hankel Determinant for Pre-Starlike Functions of Order a, Proyecciones Journal of Math., 2018, vol. 37, no. 2, pp. 305-315. DOI: 10.4067/S0716-09172018000200305.

20. MacGregor, T. H. Functions Whose Derivative Have a Positive Real Part, Transactions of the American Mathematical Society, 1962, vol. 104, no. 3, pp. 532-537. DOI: 10.1090/S0002-9947-1962-0140674-7.

21. Kilic, O. O. Sufficient Conditions for Subordination of Multivalent Functions, Journal of Inequalities and Applications, 2008, article ID 374756. DOI: 10.1155/2008/374756.

22. Duren, P. L. Univalent Functions, Grundlehren der Mathematischen Wissenschaften, vol. 259, New York, Springer-Verlag, 1983.

23. Libera, R. J. and Zlotkiewicz, E. J. Coefficient Bounds for the Inverse of a Function with Derivative in P, Proceedings of the American Mathematical Society, 1983, vol. 87, no. 2, pp. 251-257. DOI: 10.1090/S0002-9939-1983-0681830-8.

24. Libera, R. J. and Zlotkiewicz E. J. Early Coefficients of the Inverse of a Regular Convex Function, Proceedings of the American Mathematical ¡Society, 1982, vol. 85, no. 2, pp. 225-230. DOI: 10.1090/ S0002-9939-1982-0652447-5.

Received 26 November, 2018

Deekonda Vamshee Krishna GITAM Institute of Science, Visakhapatnam 530045, Andhra Pradesh, India, Assistant Professor

E-mail: vamsheekrishna1972@gmail. com

https://orcid.org/0000-0002-3334-9079;

D. Shalini

Dr. B. R. Ambedkar University, Srikakulam 532410, Andhra Pradesh, India, Teaching Assistant E-mail: shaliniraj 1005@gmail. com https://orcid.org/0000-0003-4059-8900

Владикавказский математический журнал 2020, Том 22, Выпуск 1, С. 43-48

ОПРЕДЕЛИТЕЛЬ ГАНКЕЛЯ ТРЕТЬЕГО РОДА ДЛЯ НЕКОТОРОГО ПОДКЛАССА МНОГОВАЛЕНТНЫХ АНАЛИТИЧЕСКИХ ФУНКЦИЙ

Вамши Кришна Д.1, Шалини Д.2

1 Университет ГИТАМ, Вишакхапатнам 530045, Андхра-Прадеш, Индия; 2 Университет доктора Б. Р. Амбедкэра, Шрикакулам, 532410, Андхра-Прадеш, Индия E-mail: vamsheekriskna1972@gmail.com, shaliniraj1005@gmail.com

Аннотация. Целью данной статьи является получение (не точной) верхней границы для определителя Ганкеля третьего порядка для некоторого подкласса многовалентных (p-валентных) аналитических функций, определенных на открытом единичном диске E. Используя определители Теплица, мы можем оценить определитель Ганкеля третьего рода для нормированных многовалентных аналитических функций, принадлежащих этому подклассу. Однако, используя технику, принятую Саправой [1], т. е. группируя подходящие члены для применения лемм Хаями [2], Ливингстона [3] и Померенке [4], мы видим, что оценка методом Саправы точнее, чем при применении определителей Теплица.

Ключевые слова: p-валентная аналитическая функция, верхняя граница, третий определитель Ганкеля, положительная вещественная функция.

Mathematical Subject Classification (2010): 30C45, 30C50.

Образец цитирования: Vamshee Krishna, D. and Shalini, D. Hankel Determinant of Third Kind for Certain Subclass of Multivalent Analytic Functions // Владикавк. мат. журн.—2019.—Т. 21, № 3.—C. 43-48 (in English). DOI: 10.23671/VNC.2020.1.57538.

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