Abstract
The aim of this work is to discuss some conditions for Touchard polynomials to be in the classes and . Also, we obtain some connection between and . Also, we investigate several mapping properties involving these subclasses. Further, we discuss the geometric properties of an integral operator related to the Touchard polynomial. Additionally, briefly mentioned are specific instances of our primary results. Also, several particular examples are presented.
Keywords:
star-like functions of complex order b; analytic functions; convex functions of complex order b; differential equation; convolution; Touchard polynomials MSC:
30C45; 30C80
1. Introduction
We denote by the class of functions of the following form:
Additionally, we let T denote the subclass of , which consists of functions f with the following power series expansion:
For the function involved in (1) and the function given as follows:
the convolution (or, equivalently, the Hadamard product) of the functions and is defined below:
and the integral convolution is (see [1])
Definition 1
([2,3]). A function if it satisfies:
is called star-like of complex order b.
Definition 2
([4,5]). A function if it satisfies:
is called convex of complex order b.
Definition 3
([6,7]). A function if it satisfies:
is called close-to-convex of complex order b.
Definition 4
(with [8]). A function if it satisfies:
Definition 5
(with [8]). A function if it satisfies:
Further, we denote by
Note that:
(1) , was investigated by Altintas [9] with ] (see also [10] [with ]);
(2) , and (see [2,4,6]);
(3) (see [1]);
(4) , where is the class of spiral-like functions ( is the real value) (see [11]);
(5) (see [12]);
(6) , where is the class of spiral-like functions of order ( is the real value) (see [13]);
(7) (see [1]);
(8) , where is the class of Robertson-type functions ( is the real value) (see [14]);
(9) (see [12]);
(10) (see [6]);
(11) (see [6]);
(12) (see [6]);
(13) (see [15]);
(14) (see [16]).
Definition 6
([17]). A function if it satisfies:
Note that:
(1) (see [18]);
(2) (see [19]).
In 1939, Jacques Touchard [20] studied the Touchard polynomials, also called Bell polynomials [21,22,23], consisting of a binomial-type polynomial sequence defined by
where is a Stirling number of the second kind.
If X is a random variable with a Poisson distribution with an expected value , then its th moment is , leading to the definition:
In order to study the different inventory problems of the permutations when the cycles have specific features, Jacques Touchard studied these polynomials and generalized the Bell polynomials. In addition, he developed and researched a class of related polynomials. This new approach can be used to solve integral equations, both linear and nonlinear. Since it is difficult to solve integral equations analytically, we must often find approximations for the solutions. In this situation, the linear Volterra integro-differential equation is solved using the Touchard polynomial approach. Both linear and nonlinear Volterra integral equations have been solved using the Touchard polynomial method.
Lately, Murugusundaramoorthy and Porwal [24] introduced and defined a function as follows:
The above series convergence is infinite according to the ratio test. Also, they introduced as follows:
Next, we define the convolution operator for functions f given by (2) as follows
Also, we define the functions
and
Also, we define by the convolution as
and by the integral convolution as
Also, we define by the convolution as
and by the integral convolution as
Definition 7.
The moment of the Poisson distribution about the origin is
In our study, we will use the following lemmas.
Lemma 1
Lemma 2
Lemma 3
The important area of study is the use of special functions in geometric function theory. It is applied in fields including physics, engineering, and mathematics. Several types of special functions, including generalized hypergeometric Gaussian functions [25] and references, are cited therein. In fact, after the appearance of Porwal [26], several researchers familiarized themselves with the the Poisson distribution series [27,28], Mittag-Leffler-type Poisson distribution series [29], Pascal distribution series [30], generalized distribution series [31,32], and binomial distribution series [33], and provide applications for certain classes of univalent functions. In 1939, Jacques Touchard [20] studied the Touchard polynomials. Volterra integral equations, both linear and nonlinear, have been solved using the Touchard polynomial approach. In 2022, Porwal and Murugusundaramoorthy [23] investigated some conditions for Touchard polynomials to be in the subclasses of analytic functions.
The aim of this work is to discuss some conditions for Touchard polynomials to be in the classes and . Also, we obtain some connection between and and investigate several mapping properties involving these subclasses. Further, we discuss the geometric properties of an integral operator related to the Touchard polynomial. In addition, briefly mentioned are specific instances of our primary results and several particular examples are presented.
2. Main Results
Unless mentioned, let , and .
Theorem 1.
The function if and only if
Proof.
To prove that , from Lemma 1 and (6), we have to prove that
□
Corollary 1.
Let in Theorem 1, then if and only if
Remark 1.
Putting and in Corollary 1, we improve the result due to Porwal and Murugusundaramoorthy [23] [Theorem 2.2]
Corollary 2.
Let in Theorem 1, then if and only if
Corollary 3.
Let and in Theorem 1, then if and only if
Example 1.
(1) Let and in Corollary 3, then if and only if
(2) Let and in Corollary 3, then if
Corollary 4.
Let in Theorem 1, then if and only if
Corollary 5.
Let and in Theorem 1, then if and only if
Example 2.
(1) Let and in Corollary 5, then if and only if
(2) Let and in Corollary 5, then if
Theorem 2.
The function if and only if
Proof.
To prove that , from Lemma 2 and (6), we have to prove that
□
Corollary 6.
Let in Theorem 2, then if and only if
Corollary 7.
Let in Theorem 2, then if and only if
Corollary 8.
Let and in Theorem 2, then if and only if
Example 3.
(1) Let and in Corollary 8, then if and only if
(2) Let and in Corollary 8, then if and only if
Theorem 3.
Let defined by (7) be in if and only if
Proof.
From Lemmas 2, 3, and (7), we have to prove that
□
Corollary 9.
Let in Theorem 3 and , then is in if and only if
Corollary 10.
Let in Theorem 3 and , then be in if and only if
Corollary 11.
Let and in Theorem 3 and , then is in if and only if
Theorem 4.
The function maps to if and only if
Proof.
Corollary 12.
Let in Theorem 4, then maps to if and only if
Corollary 13.
Let in Theorem 4, then maps to if and only if
Corollary 14.
Let and in Theorem 4, then maps to if and only if
Corollary 15.
Let in Theorem 4, then maps to if and only if
Corollary 16.
Let and in Theorem 4, then maps to if and only if
Theorem 5.
The function maps to if and only if
Proof.
Corollary 17.
Let in Theorem 5, then maps to if and only if
Corollary 18.
Let in Theorem 5, then maps to if and only if
Corollary 19.
Let and in Theorem 5, then maps to if and only if
Theorem 6.
The inequality (11) satisfies if and only if
(i) the function maps to
(ii) the function maps to
Proof.
(i) From Lemma 2 and (7), we have to prove that
Since , then . The proof of Theorem 6 is similar to Theorem 2, so we omit it.
(ii) The proof is similar to Theorem 2, using and (8), so we omit it. □
Corollary 20.
Let in Theorem 6, then
(i) the function maps to
(ii) the function maps to
if the inequality (12) holds.
Corollary 21.
Let in Theorem 6, then
(i) the function maps to
(ii) the function maps to
if the inequality (13) holds.
Corollary 22.
Let and in Theorem 6, then
(i) the function maps to
(ii) the function maps to
if the inequality (14) holds.
Theorem 7.
The function maps to if and only if
Proof.
Corollary 23.
Let in Theorem 7, then maps to if and only if
Corollary 24.
Let in Theorem 7, then maps to if and only if
Corollary 25.
Let and in Theorem 7, then maps to if and only if
Theorem 8.
The function is in if and only if (18) holds.
Proof.
It is easy to see that
Using Lemma 2, we only need to show that
The proof is similar to Theorem 7, so we omit it. □
3. Conclusions
Several applications of analytic functions have been studied by several authors. In our study, we apply some applications to investigate some conditions of a power series associated with Touchard polynomials belonging to classes of analytic functions of complex order b, such as and . Next, we obtain some inclusion relations between the classes and . Also, we investigate several mapping properties involving these subclasses. Further, we discuss the geometric properties of an integral operator related to the Touchard polynomial. Additionally, briefly mentioned are specific instances of our primary results. Also, several particular examples are presented. In the future, we can study Touchard polynomials with several subclasses of analytic functions.
Author Contributions
Conceptualization, E.E.A., W.Y.K., R.M.E.-A., A.M.A., F.E.M. and R.A.T.; methodology, E.E.A., W.Y.K., R.M.E.-A., A.M.A., F.E.M. and R.A.T.; validation, E.E.A., W.Y.K., R.M.E.-A., A.M.A., F.E.M., and R.A.T.; investigation, E.E.A., W.Y.K., R.M.E.-A., A.M.A., F.E.M. and R.A.T.; resources, E.E.A., W.Y.K., R.M.E.-A., A.M.A., F.E.M. and R.A.T.; writing—original draft preparation, E.E.A., W.Y.K., R.M.E.-A., A.M.A., F.E.M. and R.A.T.; writing—review and editing, E.E.A., W.Y.K., R.M.E.-A., A.M.A., F.E.M. and R.A.T.; supervision, E.E.A., W.Y.K., R.M.E.-A., A.M.A., F.E.M. and R.A.T.; project administration, E.E.A. and A.M.A. All authors have read and agreed to the published version of the manuscript.
Funding
This research has been funded by Scientific Research Deanship at University of Ha’il—Saudi Arabia through project number RG-23 033.
Data Availability Statement
Data are contained within the article.
Acknowledgments
This research has been funded by Scientific Research Deanship at University of Ha’il—Saudi Arabia through project number RG-23 033.
Conflicts of Interest
The authors declare no conflict of interest.
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