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Search Results: 1 - 10 of 325335 matches for " S Ponnusamy "
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Region of variability for functions with positive real part
S. Ponnusamy,A. Vasudevarao
Mathematics , 2010,
Abstract: For $\gamma\in\IC$ such that $|\gamma|<\pi/2$ and $0\leq\beta<1$, let ${\mathcal P}_{\gamma,\beta} $ denote the class of all analytic functions $P$ in the unit disk $\mathbb{D}$ with $P(0)=1$ and $$ {\rm Re\,} \left (e^{i\gamma}P(z)\right)>\beta\cos\gamma \quad \mbox{ in ${\mathbb D}$}. $$ For any fixed $z_0\in\mathbb{D}$ and $\lambda\in\overline{\mathbb{D}}$, we shall determine the region of variability $V_{\mathcal{P}}(z_0,\lambda)$ for $\int_0^{z_0}P(\zeta)\,d\zeta$ when $P$ ranges over the class $$ \mathcal{P}(\lambda) = \left\{ P\in{\mathcal P}_{\gamma,\beta} :\, P'(0)=2(1-\beta)\lambda e^{-i\gamma}\cos\gamma \right\}. $$ As a consequence, we present the region of variability for some subclasses of univalent functions. We also graphically illustrate the region of variability for several sets of parameters.
Univalent harmonic mappings with integer or half-integer coefficients
S. Ponnusamy,J. Qiao
Mathematics , 2012,
Abstract: Let ${\mathcal S}$ denote the set of all univalent analytic functions $f(z)=z+\sum_{n=2}^{\infty}a_n z^n$ on the unit disk $|z|<1$. In 1946 B. Friedman found that the set $\mathcal S$ of those functions which have integer coefficients consists of only nine functions. In a recent paper Hiranuma and Sugawa proved that the similar set obtained for the functions with half-integer coefficients consists of twelve functions in addition to the nine. In this paper, the main aim is to discuss the class of all sense-preserving univalent harmonic mappings $f$ on the unit disk with integer or half-integer coefficients for the analytic and co-analytic parts of $f$. Secondly, we consider the class of univalent harmonic mappings with integer coefficients, and consider the convexity in real direction and convexity in imaginary direction of these mappings. Thirdly, we determine the set of univalent harmonic mappings with half-integer coefficients which are convex in real direction or convex in imaginary direction.
Univalence of the average of two analytic functions
M. Obradovi?,S. Ponnusamy
Mathematics , 2012,
Abstract: Let $\mathcal{A}$ denote the set of all analytic functions $f$ in the unit disk $\ID=\{z:\,|z|<1\}$ of the form $f(z)=z+\sum_{n=2}^{\infty}a_nz^n.$ Let $\mathcal{U}$ denote the set of all $f\in \mathcal{A}$, $f(z)/z\neq 0$ and satisfying the condition $$ | f'(z) (\frac{z}{f(z)})^{2}-1 | < 1 {for $z\in \ID$}. $$ Functions in ${\mathcal U}$ are known to be univalent in $\ID$. For $\alpha \in [0,1]$, let $$ \mathcal{N}(\alpha)= \{f_\alpha :\, f_\alpha (z)=(1-\alpha)f(z)+\alpha \int_0^z\frac{f(t)}{t}\,dt, {$f\in\mathcal{A}$ with $|a_n|\leq n$ for $n\geq 2$}\}. $$ In this paper, we first show that the condition $\sum_{n=2}^{\infty}n|a_n|\leq 1$ is sufficient for $f$ to be in ${\mathcal U}$ and the same condition is necessary for $f\in {\mathcal U}$ in case all $a_n$'s are negative. Next, we obtain the radius of univalence of functions in the class $\mathcal{N}(\alpha)$. Also, for $f,g\in \mathcal{U}$ with $\frac{f(z)+g(z)}{z}\neq 0$ in $\ID$, $F(z)=(f(z)+g(z))/2$, and $G(z)=r^{-1}F(rz)$, we determine a range of $r$ such that $G\in {\mathcal U}$. As a consequence of these results, several special cases are presented.
Distortion and covering theorems of pluriharmonic mappings
Sh. Chen,S. Ponnusamy
Mathematics , 2014,
Abstract: In this paper, we mainly investigate distortion and covering theorems on some classes of pluriharmonic mappings.
On harmonic combination of univalent functions
M. Obradovi?,S. Ponnusamy
Mathematics , 2011,
Abstract: Let ${\mathcal S}$ be the class of all functions $f$ that are analytic and univalent in the unit disk $\ID$ with the normalization $f(0)=f'(0)-1=0$. Let $\mathcal{U} (\lambda)$ denote the set of all $f\in {\mathcal S}$ satisfying the condition $$|f'(z)(\frac{z}{f(z)})^{2}-1| <\lambda ~for $z\in \ID$, $$ for some $\lambda \in (0,1]$. In this paper, among other things, we study a "harmonic mean" of two univalent analytic functions. More precisely, we discuss the properties of the class of functions $F$ of the form $$\frac{z}{F(z)}=1/2(\frac{z}{f(z)}+\frac{z}{g(z)}), $$ where $f,g\in \mathcal{S}$ or $f,g\in \mathcal{U}(1)$. In particular, we determine the radius of univalency of $F$, and propose two conjectures concerning the univalency of $F$.
Convolutions of slanted half-plane harmonic mappings
Liulan Li,S. Ponnusamy
Mathematics , 2012,
Abstract: Let ${\mathcal S^0}(H_{\gamma})$ denote the class of all univalent, harmonic, sense-preserving and normalized mappings $f$ of the unit disk $\ID$ onto the slanted half-plane $H_\gamma :=\{w:\,{\rm Re\,}(e^{i\gamma}w) >-1/2\}$ with an additional condition $f_{\bar{z}}(0)=0$. Functions in this class can be constructed by the shear construction due to Clunie and Sheil-Small which allows by examining their conformal counterpart. Unlike the conformal case, convolution of two univalent harmonic convex mappings in $\ID$ is not necessarily even univalent in $\ID$. In this paper, we fix $f_0\in{\mathcal S^0}(H_{0})$ and show that the convolutions of $f_0$ and some slanted half-plane harmonic mapping are still convex in a particular direction. The results of the paper enhance the interest among harmonic mappings and, in particular, solves an open problem of Dorff, et. al. \cite{DN} in a more general setting. Finally, we present some basic examples of functions and their corresponding convolution functions with specified dilatations, and illustrate them graphically with the help of MATHEMATICA software. These examples explain the behaviour of the image domains.
Uniform close-to-convexity radius of sections of functions in the close-to-convex family
s. V. Bharanedhar,S. Ponnusamy
Mathematics , 2014,
Abstract: The authors consider the class $\F$ of normalized functions $f$ analytic in the unit disk $\ID$ and satisfying the condition $${\rm Re}\left(1+\frac{zf''(z)}{f'(z)}\right)>-\frac{1}{2},\quad z\in\D. $$ Recently, Ponnusamy et al. \cite{samy-hiroshi-swadesh} have shown that $1/6$ is the uniform sharp bound for the radius of convexity of every section of each function in the class $\F$. They conjectured that $1/3$ is the uniform univalence radius of every section of $f\in \F$. In this paper, we solve this conjecture affirmatively.
Modified Dini functions: monotonicity patterns and functional inequalities
á. Baricz,S. Ponnusamy,S. Singh
Mathematics , 2014,
Abstract: We deduce some new functional inequalities, like Tur\'an type inequalities, Redheffer type inequalities, and a Mittag-Leffler expansion for a special combination of modified Bessel functions of the first kind, called modified Dini functions. Moreover, we show the complete monotonicity of a quotient of modified Dini functions by introducing a new continuous infinitely divisible probability distribution. The key tool in our proofs is a recently developed infinite product representation for a special combination of Bessel functions of the first, which was very useful in determining the radius of convexity of some normalized Bessel functions of the first kind.
Coefficient Conditions for Harmonic Univalent Mappings and Hypergeometric Mappings
S. V. Bharanedhar,S. Ponnusamy
Mathematics , 2011,
Abstract: In this paper, we obtain coefficient criteria for a normalized harmonic function defined in the unit disk to be close-to-convex and fully starlike, respectively. Using these coefficient conditions, we present different classes of harmonic close-to-convex (resp. fully starlike) functions involving Gaussian hypergeometric functions. In addition, we present a convolution characterization for a class of univalent harmonic functions discussed recently by Mocanu, and later by Bshouty and Lyzzaik in 2010. Our approach provide examples of harmonic polynomials that are close-to-convex and starlike, respectively.
Sufficiency for Gaussian hypergeometric functions to be uniformly convex
Yong Chan Kim,S. Ponnusamy
International Journal of Mathematics and Mathematical Sciences , 1999, DOI: 10.1155/s0161171299227652
Abstract: Let F(a,b;c;z) be the classical hypergeometric function and f be a normalized analytic functions defined on the unit disk ° ’ °. Let an operator Ia,b;c(f) be defined by [Ia,b;c(f)](z)=zF(a,b;c;z)*f(z). In this paper the authors identify two subfamilies of analytic functions ¢ ±1 and ¢ ±2 and obtain conditions on the parameters a,b,c such that f ¢ ¢ ±1 implies Ia,b;c(f) ¢ ¢ ±2.
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