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Convolution conditions for two subclasses of analytic functions defined by Jackson q-difference operator
Journal of the Egyptian Mathematical Society volume 30, Article number: 7 (2022)
Abstract
By using Jackson q-derivative, some characterizations in terms of convolutions for two classes of analytic functions in the open unit disc are given. Also, coefficient conditions and inclusion properties for functions in these classes are found.
Introduction
Let A be the class of functions of the form:
which are analytic in the open unit disc
Jackson q-derivative of a function f is given by (see [1, 2])
If \(\ f(z)=z^{n}\), then
where
Using the observation
we have
If the function f defined by (1), then
Also, we have the following q-derivative rules
and
The q-difference operator \(D_{q}\) has been extensively investigated in the field of geometric function theory by many authors. For some recent works related to this operator on the classes of analytic functions, we refer to [3,4,5,6,7].
The Hadamard product (or convolution) of two functions \(f,g\in A,\) denoted by \(f*g,\) is
where f is given by (1) and \(g(z)=z+\sum \limits _{k=2}^{\infty }b_{k}z^{k}\). Govindaraj and Sivasubramanian [8] defined the differential operator \(S_{q}^{n}f(z):A\rightarrow A\) by:
and for \(n\in N_{0}=\{0,1,\ldots \}\)
where
The differential operator \(S_{q}^{n}\) is called Salagean q-differential operator.
Definition 1
For \(f\in A\), we say f belongs to class \(S_{\lambda ,\zeta }^{*}(A,B)\), if and only if
where \(0<\zeta<1,0\le \lambda \le 1,-1\le B<A\le 1,D_{\zeta }\) is Jackson q-derivative with \(q=\zeta\) and \(\prec\) denotes the usual subordination (see [9,10,11]).
It is noticed that, by giving specific values to A, B and \(\lambda\) we obtain the following important subclasses studied by various authors in earlier works:
-
1.
\(S_{0,q}^{*}(1-2\alpha ,-1)\equiv S_{q}^{*}(\alpha )\) and \(S_{1,q}^{*}(1-2\alpha ,-1)\equiv C_{q}(\alpha )\) are, respectively, the classes of q-starlike and q-convex functions (see Seoudy and Aouf [12] and Ramachandran et al. [13])
-
2.
\(S_{0,q}^{*}(A,B)\equiv S_{q}^{*}[A,B]\) and \(S_{1,q}^{*}(A,B)\equiv C[A,B]\) the classes of q-starlike and q-convex functions which are associated with the Janowski functions (see Srivastava et al. [14])
-
3.
\(S_{0,q}^{*}(\frac{b^{2}-a^{2}+a}{b},\frac{1-a}{b})\equiv S_{q}^{*}(\alpha ),\) where \(a=\frac{1-\alpha q}{1-q}\) and \(b=\frac{ 1-\alpha }{1-q}\) (see Polatoglu et al. [15])
-
4.
\(\underset{\zeta \rightarrow 1^{-}}{\lim }S_{\alpha ,\zeta }^{*}([b(1+m)-m],-m)\equiv S_{M}^{*}(\alpha ,b),\)where \(b\in {\mathbb {C}},m=1- \frac{1}{M}\) and \(M>\frac{1}{2}\) (see Lashin [16])
-
5.
\(\underset{\zeta \rightarrow 1^{-}}{\lim }S_{0,\zeta }^{*}([b(1+m)-m],-m)\equiv F^{*}(b,M),\)where \(m=1-\frac{1}{M}\) and \(M>\frac{1 }{2}\) (see Nasr and Aouf [17])
-
6.
\(\underset{\zeta \rightarrow 1^{-}}{\lim }S_{0,\zeta }^{*}(1-2\alpha ,-1)\equiv S^{*}(\alpha )\) and \(\underset{\zeta \rightarrow 1^{-}}{\lim }S_{1,\zeta }^{*}(1-2\alpha ,-1)\equiv C(\alpha )(0\le \alpha <1)\) the classes of starlike and convex functions of order \(\alpha\) (see Robertson [18] ).
-
7.
\(\underset{\zeta \rightarrow 1^{-}}{\lim }S_{0,\zeta }^{*}(1,-1)\equiv S^{*}\) and \(\underset{\zeta \rightarrow 1^{-}}{\lim } S_{1,\zeta }^{*}(1,-1)\equiv C\) the usual classes of starlike, convex and spirallike functions (see Goodman [19]).
With the help of the Salagean \(\zeta\)-differential operator \(S_{\zeta }^{n}\) given by (3), we say that a function \(f\in A\) is in the class \(S_{\lambda ,\zeta }^{*}(n,A,B)\) if and only if
where \(0<\zeta <1,\) \(-1\le B<A\le 1,0\le \lambda \le 1\) and \(n\in N_{0}.\)
We note that
-
1.
\(\underset{\zeta \rightarrow 1^{-}}{\lim }S_{\lambda ,\zeta }^{*}(n,1-2\alpha ,-1)\) \(\equiv S_{n}(\lambda ,\alpha )\) (see Wang and Aghalary [20]).
-
2.
\(\underset{\zeta \rightarrow 1^{-}}{\lim }S_{\lambda ,\zeta }^{*}(0,1-2\alpha ,-1)\equiv T(\lambda ,\alpha )\) (see Altintas [21])
-
3.
\(\underset{\zeta \rightarrow 1^{-}}{\lim }S_{\lambda ,\zeta }^{*}(1,1-2\alpha ,-1)\equiv C(\lambda ,\alpha )\) (see Kamali and Akbulut [22])
Methods
The aim of the present paper is to obtain convolution properties, necessary and sufficient conditions, coefficient estimates, and inclusion properties of functions belonging to the class \(S_{\lambda ,\zeta }^{*}(n,A,B)\) with techniques similar to those used by Silverman et al. [23].
Results and discussion
Proposition 2
If \(f\in A,\) then
and
Proof
To prove the first part, we write
It is well Known that
then
To prove the second part, we write
Now, we will prove that \(\mu _{k}=\frac{[k]_{\zeta }[k+1]_{\zeta }}{ [2]_{\zeta }},\) where \(\mu _{k}\) is the coefficient of \(z^{k}\) i.e. will prove
From (8), we find that \([2]_{\zeta }\mu _{1}=[1]_{\zeta }[2]_{\zeta }.\) Next assume that (8) is true for \(k=m.\) Then
Hence, by induction, the result is valid for all k, which ends the proof. \(\square\)
Theorem 3
A function f of the form (1) in the class \(S_{\lambda ,\zeta }^{*}(A,B)\) if and only if
where \(C=C_{\theta }=\tfrac{{\mathrm{e}}^{-i\theta }+A}{A-B},\ \theta \in [0,2\pi ).\)
Proof
The function f belongs to the class \(S_{\lambda ,\zeta }^{*}(A,B)\) if and only if
Thus f \(\in S_{\lambda ,\zeta }^{*}(A,B)\) is equivalent to
This simplifies to
Since
From (6), It follows that
(see also Piejko et al. [24]). Using (11) and (12), we obtain
Using the identity \(zD_{\zeta }(f*g)=f*zD_{\zeta }g,\) we conclude that
Substituting (13) and (14) into (10), we get
So that the left hand side of (15) may be expressed as
or, equivalently,
Then (15) can be rewritten as the following
where \(z\in {\mathbb {U}},\ \theta \in [0,2\pi ).\) Hence the proof of Theorem 3 is complete. \(\square\)
Taking \(\lambda =0\) in Theorem 3, we get the following corollary
Corollary 4
A function f of the form (1) in the class \(S_{\zeta }^{*}(A,B)\) if and only if
where \(C=C_{\theta }=\tfrac{{\mathrm{e}}^{-i\theta }+A}{A-B},\ \theta \in [0,2\pi ).\)
Remark 5
Letting \(A=b(1+m)-m\) and \(B=-m\) with \(m=1-\frac{1}{M}\) and \(M>\frac{1}{2}\) in Corollary 4 we get the result obtained by Aouf and Seoudy [25, Theorem 2.1].
Taking \(\lambda =1\) in Theorem 3, we get the following corollary
Corollary 6
A function f of the form (1) is in the class \(C_{\zeta }(A,B)\) if and only if  \(\frac{1}{z}\left[ {f(z)*\frac{{z + \zeta [1 - (1 + \zeta )C]{z^2}}}{{(1 - z)(1 - \zeta z)(1 - {\zeta ^2}z)}}} \right] \ne 0\quad (z \in {\mathbb{U}})\)
where \(C=C_{\theta }=\tfrac{{\mathrm{e}}^{-i\theta }+A}{A-B},\ \theta \in [0,2\pi ).\)
Remark 7
Letting \(A=b(1+m)-m\) and \(B=-m\) with \(m=1-\frac{1}{M}\) and \(M>\frac{1}{2}\) in Corollary 6 we get the result obtained by Aouf and Seoudy [25, Theorem 2.4].
Remark 8
-
1
Letting \(\zeta \rightarrow 1^{-1},A=[b(1+m)-m]\) and \(B=-m\) with \(m=1- \frac{1}{M}\) and \(M>\frac{1}{2}\) in Theorem 3, we obtain the result obtained by Lashin [16].
-
2
Letting \(\zeta \rightarrow 1^{-1},A=[b(1+m)-m]\) and \(B=-m\) with \(m=1- \frac{1}{M}\) and \(M>\frac{1}{2}\) in Corollaries 4 and 6, respectively, we obtain the results obtained by El-Ashwah [26, Theorem 2.1 and Theorem 2.4].
-
3
Taking \(\zeta \rightarrow 1^{-1},A=1-2\alpha ,B=-1\) and \({\mathrm{e}}^{i\theta }=x(\left| x\right| =1)\) in Corollaries 4 and 6, we obtain the results obtained by Silverman et al. [23, Theorems 1,2].
-
4
Taking \(\zeta \rightarrow 1^{-1}\)and \({\mathrm{e}}^{i\theta }=x(\left| x\right| =1)\) in Corollaries 4 and 6, respectively, we obtain the results obtained by Padmanabhan and Ganesan [27, Theorem 1,2].
Theorem 9
A necessary and sufficient condition for the function f of the form (1) to be in the class \(S_{\lambda ,\zeta }^{*}(n,A,B)\) is
for all \(\theta \in [0,2\pi )\) and \(z\in U.\)
Proof
From Theorem 3, we have \(f(z)\in\)\(S_{\lambda ,\zeta }^{*}(n,A,B)\)if and only if
where \(C=C_{\theta }=\tfrac{{\mathrm{e}}^{-i\theta }+A}{A-B},\ \theta \in [0,2\pi ).\) Now, we can easily deduce that
Using Proposition 2 and the relation \(\frac{z}{(1-z)} =z+\sum \nolimits _{k=2}^{\infty }z^{k}\), (18) can be written as
Setting \([k]_{\zeta }=\frac{1-\zeta ^{k}}{1-\zeta }\) and \([k+1]_{\zeta }= \frac{1-\zeta ^{k+1}}{1-\zeta },\) (19) gives
which is equivalent to
Thus (17) together with (20) lead to (16). This completes the proof of Theorem 9. \(\square\)
Theorem 10
If the function f defined by (1) satisfies the inequality
then \(f(z) \in S_{{\lambda ,\zeta }}^{*} (n,A,B).\)
Proof
Since
then
Thus (16) holds, which ends the proof. \(\square\)
Theorem 11
\(S_{\lambda ,\zeta }^{*}(n+1,A,B)\subset S_{\lambda ,\zeta }^{*}(n,A,B).\)
Proof
Since \(f(z)\in S_{\lambda ,\zeta }^{*}(n+1,A,B),\)It follows from Theorem 9, that
(22) can be written as
(23) gives
which means that \(f(z)\in S_{\lambda ,\zeta }^{*}(n,A,B).\) This completes the proof of Theorem 11. \(\square\)
Conclusions
q- Derivatives and q-integrals play an important and significant role in the study of quantum groups and q-deformed super-algebras. Recently, q-calculus has attracted the attention of many researchers in the field of geometric function theory. In this paper, we have used q-calculus to define and study some new sub-classes of analytic functions. Using the convolution technique some interesting properties of these new classes have been derived. Also, Coefficient conditions and inclusion properties of functions in these classes are found. Some special cases have been discussed as applications of our main results.
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El-Emam, F.Z. Convolution conditions for two subclasses of analytic functions defined by Jackson q-difference operator. J Egypt Math Soc 30, 7 (2022). https://doi.org/10.1186/s42787-022-00141-2
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DOI: https://doi.org/10.1186/s42787-022-00141-2
Keywords
- Jackson q-derivative
- q-starlike and convex functions
- Convolution
- Inclusion relations
- Salagean q-differential operator
Mathematics Subject Classification
- Primary 30C45
- 30C55