Uniformly Starlike and Uniformly Convex Functions
V.B.L. Chaurasia and Amber Srivastava vol. 9, iss. 1, art. 30, 2008
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UNIFORMLY STARLIKE AND UNIFORMLY CONVEX FUNCTIONS PERTAINING TO SPECIAL
FUNCTIONS
V.B.L. CHAURASIA AMBER SRIVASTAVA
Department of Mathematics Department of Mathematics
University of Rajasthan Swami Keshvanand Institute of Technology,
Jaipur-302004, India Management and Gramothan
Jagatpura, Jaipur-302025, India EMail:amber@skit.ac.in
Received: 04 September, 2006
Accepted: 14 July, 2007
Communicated by: H.M. Srivastava 2000 AMS Sub. Class.: 30C45.
Key words: Analytic functions, Univalent functions, Starlike functions, Convex functions, Integral operator, Fox-Wright function.
Abstract: The main object of this paper is to derive the sufficient conditions for the func- tionz{pψq(z)}to be in the classes of uniformly starlike and uniformly convex functions. Similar results using integral operator are also obtained.
Acknowledgements: The authors are grateful to Professor H.M. Srivastava, University of Victoria, Canada for his kind help and valuable suggestions in the preparation of this paper.
Uniformly Starlike and Uniformly Convex Functions
V.B.L. Chaurasia and Amber Srivastava
vol. 9, iss. 1, art. 30, 2008
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Contents
1 Introduction 3
2 Main Results 5
3 An Integral Operator 9
4 Particular Cases 12
Uniformly Starlike and Uniformly Convex Functions
V.B.L. Chaurasia and Amber Srivastava
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1. Introduction
LetAdenote the class of functions of the form
(1.1) f(z) = z+
∞
X
n=2
anzn, that are analytic in the open unit disk∆ ={z :|z|<1}.
Also letSdenote the subclass ofAconsisting of all functionsf(z)of the form
(1.2) f(z) = z−
∞
X
n=2
anzn, an≥0.
A function f ∈ A is said to be starlike of order α, 0 ≤ α < 1, if and only if Re
zf0(z) f(z)
> α, z ∈ ∆.Alsof of the form (1.1) is uniformly starlike, whenever f(z)−f
(ξ) (z−ξ)f0(z)
≥ 0,(z,ξ) ∈ ∆×∆.This class of all uniformly starlike functions is denoted byU ST [4] (see also [5], [10] and [14]).
The functionf of the form (1.1) is uniformly convex in∆whenever Re
1 + (z−ξ)f00(z) f0(z)
≥0, (z,ξ)∈∆×∆.
This class of all uniformly convex functions is denoted by U CV [3] (also refer [2], [6], [9] and [13]). Further it is said to be in the class U CV(α), α ≥ 0 if Re
1 + zff(z)0(z)
≥α
zf00(z) f0(z)
.
A functionf of the form (1.2) is said to be in the classU ST N(α),0≤α≤1, if Re
f(z)−f
(ξ) (z−ξ)f0(z)
≥α,(z,ξ)∈∆×∆.
Uniformly Starlike and Uniformly Convex Functions
V.B.L. Chaurasia and Amber Srivastava
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In the present paper, we shall use analogues of the lemmas in [8] and [7] respec- tively in the following form.
Lemma 1.1. A functionf of the form (1.1) is in the classU ST(α), if
∞
X
n=2
[(3−α)n−2]|an| ≤(1−α)M1,
whereM1 >0is a suitable constant. In particular,f ∈U ST whenever
∞
X
n=2
(3n−2)|an| ≤M1.
Lemma 1.2. A sufficient condition for a function f of the form (1.1) to be in the classU CV(α)is thatP∞
n=2n[(α+ 1)n−α]an≤M2,whereM2 >0is a suitable constant. In particular,f ∈U CV wheneverP∞
n=2n2an≤M2.
The Fox-Wright function [12, p. 50, equation 1.5] appearing in the present paper is defined by
(1.3) pψq(z) = pψq
(aj, αj)1,p; (bj, βj)1,q; z
=
∞
X
n=0
Qp
j=1Γ(aj +αjn)zn Qq
j=1Γ(bj +βjn)n!,
where αj (j = 1, . . . , p) and βj (j = 1, . . . , q) are real and positive and 1 + Pq
j=1βj >Pp j=1αj.
Uniformly Starlike and Uniformly Convex Functions
V.B.L. Chaurasia and Amber Srivastava
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2. Main Results
Theorem 2.1. If
q
X
j=1
|bj|>
p
X
j=1
|aj|+ 1, aj >0 and 1 +
q
X
j=1
βj >
p
X
j=1
αj,
then a sufficient condition for the functionz{ pψq(z)} to be in the classU ST(α), 0≤α <1, is
(2.1)
3−α 1−α
pψq
(|aj +αj|, αj)1,p; (|bj+βj|, βj)1,q; 1
+ pψq
(|aj|, αj)1,p; (|bj|, βj)1,q; 1
≤M1+ Qp
j=1Γaj Qq
j=1Γbj. Proof. Since
z{pψq(z)}= Qp
j=1Γaj
j=1Γbjz+
∞
X
n=2
Qp
j=1Γ[aj +αj(n−1)]zn Qq
j=1Γ[bj+βj(n−1)](n−1)!
so by virtue of Lemma1.1, we need only to show that (2.2)
∞
X
n=2
[(3−α)n−2]
Qp
j=1Γ[aj +αj(n−1)]
j=1Γ[bj+βj(n−1)](n−1)!
≤(1−α)M1. Now, we have
∞
X
n=2
[(3−α)n−2]
Qp
j=1Γ[aj+αj(n−1)]
j=1Γ[bj+βj(n−1)](n−1)!
Uniformly Starlike and Uniformly Convex Functions
V.B.L. Chaurasia and Amber Srivastava
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=
∞
X
n=0
[(3−α)(n+ 2)−2]
Qp
j=1Γ[aj+αj(n+ 1)]
j=1Γ[bj+βj(n+ 1)](n+ 1)!
= (3−α)
∞
X
n=0
Qp
j=1Γ[(aj+αj) +nαj] Qq
j=1Γ[(bj+βj) +nβj]n!
+ (1−α)
" ∞ X
n=0
Qp
j=1Γ(aj+αjn) Qq
j=1Γ(bj +βjn)
1 n! −
Qp j=1Γaj Qq
j=1Γbj
#
= (3−α) pψq
(|aj +αj|, αj)1,p; (|bj +βj|, βj)1,q; 1
+ (1−α) pψq
(|aj|, αj)1,p; (|bj|, βj)1,q; 1
−(1−α) Qp
j=1Γaj
Qq j=1Γbj
≤(1−α)M1
which in view of Lemma1.1gives the desired result.
Theorem 2.2. If
q
X
j=1
bj >
p
X
j=1
aj+ 1, aj >0 and 1 +
q
X
j=1
βj >
p
X
j=1
αj,
then a sufficient condition for the functionz{pψq(z)}to be in the classU ST N(α), 0≤α <1, is:
3−α 1−α
pψq
(aj +αj, αj)1,p; (bj+βj, βj)1,q; 1
+ pψq
(aj, αj)1,p; (bj, βj)1,q; 1
≤M1+ Qp
j=1Γaj Qq
j=1Γbj. Proof. The proof of Theorem2.2is a direct consequence of Theorem2.1.
Uniformly Starlike and Uniformly Convex Functions
V.B.L. Chaurasia and Amber Srivastava
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Theorem 2.3. If
q
X
j=1
bj >
p
X
j=1
aj + 2, aj >0 and 1 +
q
X
j=1
βj >
p
X
j=1
αj,
then a sufficient condition for the function z{pψq(z)} to be in the classU CV(α), 0≤α <1, is
(2.3) (1 +α)pψq
(aj+ 2αj, αj)1,p; (bj + 2βj, βj)1,q; 1
+ (2α+ 3) pψq
(aj+αj, αj)1,p; (bj +βj, βj)1,q; 1
+ pψq(1)≤M2+ Qp
j=1Γaj
j=1Γbj. Proof. By virtue of Lemma1.2, it suffices to prove that
(2.4)
∞
X
n=2
n[(α+ 1)n−α]
Qp
j=1Γ[aj +αj(n−1)]
j=1Γ[bj+βj(n−1)](n−1)! ≤M2. Now, we have
(2.5)
∞
X
n=2
n[(α+ 1)n−α]
Qp
j=1Γ[aj +αj(n−1)]
j=1Γ[bj +βj(n−1)](n−1)!
= (1 +α)
∞
X
n=1
(n+ 1)2 Qp
j=1Γ(aj +αjn) Qq
j=1Γ[(bj+βjn)n!
−α
∞
X
n=1
(n+ 1) Qp
j=1Γ(aj+αjn) Qq
j=1Γ(bj+βjn)n!.
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Using(n+ 1)2 =n(n+ 1) + (n+ 1), (2.5) may be expressed as (1+α)
∞
X
n=1
(n+ 1)
Qp
j=1Γ(aj +αjn) Qq
j=1Γ(bj +βjn)(n−1)!
(2.6)
+
∞
X
n=1
(n+ 1) Qp
j=1Γ(aj +αjn) Qq
j=1Γ(bj +βjn)n!
= (1 +α)
∞
X
n=2
Qp
j=1Γ(aj +αjn) Qq
j=1Γ(bj +βjn)(n−2)!
+ (2α+ 3)
∞
X
n=0
Qp
j=1Γ[(aj +αj) +αjn]
j=1Γ[(bj+βj) +βjn]n!
+
∞
X
n=1
Qp
j=1Γ(aj+αjn) Qq
j=1Γ(bj+βjn)n!
= (1 +α) pψq
(aj + 2αj, αj)1,p; (bj+ 2βj, βj)1,q; 1
+ (2α+ 3) pψq
(aj+αj, αj)1,p; (bj +βj, βj)1,q; 1
+ pψq(1)− Qp
j=1Γaj Qq
j=1Γbj, which is bounded above by M2 if and only if (2.3) holds. Hence the theorem is proved.
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3. An Integral Operator
In this section we obtain sufficient conditions for the function
pφq
(aj, αj)1,p; (bj, βj)1,q; z
= Z z
0
pψq(x)dx to be in the classesU ST andU CV.
Theorem 3.1. If
q
X
j=1
bj >
p
X
j=1
aj, aj >0 and 1 +
q
X
j=1
βj >
p
X
j=1
αj,
then a sufficient condition for the functionpφq(z) = Rz
0 pψq(x)dxto be in the class U ST is
(3.1) 3 pψq(1)−2pψq
(aj−αj, αj)1,p; (bj −βj, βj)1,q; 1
+ 2 Qp
j=1Γ(aj −αj) Qq
j=1Γ(bj −βj) ≤M1+ Qp
j=1Γaj Qq
j=1Γbj. Proof. Since
pφq(z) = Z z
0
pψq(x)dx (3.2)
= Qp
j=1Γaj Qq
j=1Γbjz+
∞
X
n=2
Qp
j=1Γ[(aj −αj) +αjn]
j=1Γ[(bj−βj) +βjn]
zn n!,
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V.B.L. Chaurasia and Amber Srivastava
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we have
∞
X
n=2
(3n−2) Qp
j=1Γ[(aj −αj) +αjn]
j=1Γ[(bj −βj) +βjn]n!
(3.3)
= 3
∞
X
n=1
Qp
j=1Γ(aj+αjn) Qq
j=1Γ(bj+βjn)n! −2
" ∞ X
n=0
Qp
j=1Γ[(aj −αj) +αjn]
j=1Γ[(bj−βj) +βjn]n!
− Qp
j=1Γ(aj−αj) Qq
j=1Γ(bj−βj) − Qp
j=1Γaj Qq
j=1Γbj
#
= 3 pψq(1)−2 pψq
(aj −αj, αj)1,p; (bj−βj, βj)1,q; 1
+ 2 Qp
j=1Γ(aj −αj) Qq
j=1Γ(bj −βj) − Qp
j=1Γaj Qq
j=1Γbj. In view of Lemma1.1, (3.3) leads to the result (3.1).
Theorem 3.2. If
q
X
j=1
bj >
p
X
j=1
aj, aj >0 and 1 +
q
X
j=1
βj >
p
X
j=1
αj,
then a sufficient condition for the functionpφq(z) = Rz
0 pψq(x)dxto be in the class U CV is
(3.4) pψq
(aj +αj, αj)1,p; (bj+βj, βj)1,q; 1
+ pψq(1) ≤M2+ Qp
j=1Γaj Qq
j=1Γbj.
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Proof. Sincepφq(z)has the form (3.2), then
∞
X
n=2
n2 Qp
j=1Γ[(aj −αj) +αjn]
j=1Γ[(bj−βj) +βjn]n!
(3.5)
=
∞
X
n=1
(n+ 1) Qp
j=1Γ(aj +αjn) Qq
j=1Γ(bj +βjn)n!
=
∞
X
n=0
Qp
j=1Γ[(aj +αj) +αjn]
j=1Γ[(bj+βj) +βjn]n! +
∞
X
n=0
Qp
j=1Γ(aj +αjn) Qq
j=1Γ(bj +βjn)n!− Qp
j=1Γaj Qq
j=1Γbj
= pψq
(aj+αj, αj)1,p; (bj +βj, βj)1,q; 1
+ pψq(1)− Qp
j=1Γaj Qq
j=1Γbj, which in view of Lemma1.2gives the desired result (3.4).
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4. Particular Cases
4.1. By settingα1 =α2 =· · ·=αp = 1;β1 =β2 =· · ·=βq= 1and M1 =M2 =M3 =
Qp j=1Γaj Qq
j=1Γbj,
Theorems 2.1, 2.3, 3.1 and 3.2 reduce to the results recently obtained by Shan- mugam, Ramachandran, Sivasubramanian and Gangadharan [11].
4.2. By specifying the parameters suitably, the results of this paper readily yield the results due to Dixit and Verma [1].
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References
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[2] A. GANGADHARAN, T.N. SHANMUGAMANDH.M. SRIVASTAVA, Gen- eralized hypergeometric functions associated with k-uniformly convex func- tions, Comput. Math. Appl., 44 (2002), 1515–1526.
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Uniformly Starlike and Uniformly Convex Functions
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[13] H.M. SRIVASTAVA AND A.K. MISHRA, Applications of fractional calculus to parabolic starlike and uniformly convex functions, Computer Math. Appl., 39 (2000), 57–69.
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