Search Results (135)

This investigation introduces a novel family of univalent analytic functions subordinate to lung-shaped domains within the open unit disk. Through rigorous application of subordination theory and systematic analysis, we establish coefficient bounds for the initial five coefficients, derive estimates for Hankel determinants of orders two and three, determine bounds for the first four logarithmic coefficients, and derive the bounds of some Zalcman functionals. The lung-shaped domain is characterized by the subordination condition involving a secant-based function, which maps the unit disk onto a geometrically distinctive region exhibiting bilateral symmetry. All obtained bounds are demonstrated to be sharp through the construction of specific extreme functions. Full article

This article proposes a new type of analytic function called ${\mathbb{M}}_{tan}$ and introduces a new geometric structure that blends exponential and trigonometric properties. In addition, it obtains exact bounds for all second- and third-order Hankel determinants and establishes extremal results for the Fekete–Szegö and Zalcman functionals. Moreover, it discusses the validity of the Krushkal inequality. Furthermore, it applies the developed methodology to improve the contrast and quality of color images and demonstrates that the proposed enhancement filters yield notable improvements in contrast and quality compared to other filters, based on the PSNR, SSIM, MSE, RMSE, PCC, and MAE metrics. This article demonstrates its dual nature, namely advances in geometric function theory and practical advantages in digital image processing. Full article

The primary objective of this paper is to introduce and investigate several novel subclasses of bi-univalent functions associated with the q-calculus framework. Using appropriate analytical techniques, we derive coefficient bounds for the initial coefficients of the functions belonging to these newly defined classes. In particular, we provide explicit estimates for the second-order Hankel determinant and address the classical Fekete–Szegö functional problem within the context of these classes under suitable conditions. It is important to note that the findings presented in this work not only contribute to the ongoing development of q-analogs in geometric function theory, but also serve as a unifying generalization of many previously known results, which are obtained as special cases of our main findings. Full article

This paper introduces coefficient functionals for a new subclass (${\mathcal{S}}_{tanh}^{*})$ of starlike functions associated with the tangent hyperbolic function, including the first four sharp coefficient bounds, the Fekete-Szegő problem, Zalcman inequalities, and Hankel determinants. For this class, logarithmic and inverse problems are also studied. Furthermore, we define families of functions that are related to the functions $1+sin\mu ,$${\left(1+\alpha \mu \right)}^2,1+{\displaystyle \frac{\mu }{1-\beta {\mu }^2}}$, represented by ${\mathcal{Y}}_{sin},{\mathcal{Y}}_{\alpha }$ and ${\mathcal{Y}}_{\beta }$, respectively. Using the Schwarz-Pick lemma and the theory of subordination, involving the function $1+{\displaystyle \frac{1}{2}}tanh\mu$, we find the majorization radii and construct majorization results of the form $\left|g^{\prime }\left(\mu \right)\right|\le \left|h^{\prime }\left(\mu \right)\right|$ for functions g majorized by h. Through graphical analysis, we also demonstrate that our defined class ${\mathcal{S}}_{tanh}^{*}$ is non-empty, which validates our study in this article. Full article

This paper presents a newly defined subclass of analytic functions and explores several significant properties within the class, which use for their definitions the q-analogues of the derivative and the subordinations. Thus, we tried to connect different notions of the q-calculus with those of the Geometric Function Theory of one variable function. We identify the bounds of the initial coefficients and found upper bounds of the Fekete–Szegő functional for these classes. We investigate the relationship between the coefficients of an univalent function and those of its inverse by examining the difference between their second Hankel determinants. Furthermore, we analyze the behavior of the quantity module of the difference between the second Hankel determinant of a function and the same determinant for its inverse. To improve the obtained results by finding sharp estimations remains an interesting open question. Full article

Modeling forced nonlinear multivariable dynamical systems remains challenging, particularly when first-principles models are unavailable or strong nonlinear couplings are present. In recent years, data-driven approaches grounded in the Koopman operator theory have gained attention for their ability to represent nonlinear dynamics via linear evolution in appropriately lifted spaces. This work presents a data-driven modeling framework for forced nonlinear multiple-input multiple-output (MIMO) systems based on Hankel Dynamic Mode Decomposition with control and lifting functions (HDMDc+Lift). The proposed methodology exploits Hankel matrices to encode temporal correlations and employs lifting functions to approximate the Koopman operator’s action on observable functions. As a result, an augmented-order linear state-space model is identified exclusively from input–output data, without relying on explicit knowledge of the system’s governing equations. The effectiveness of the proposed approach is demonstrated using operational data from a real multivariable tank system that was not used during the identification stage. The identified model achieves a coefficient of determination exceeding 0.87 in multi-step prediction tasks. Furthermore, spectral analysis of the resulting linear operator reveals that the dominant dynamical modes of the physical system are accurately captured. At the same time, additional modes associated with nonlinear interactions are also identified. These results highlight the HDMDc+Lift framework’s ability to provide accurate and interpretable linear representations of forced nonlinear MIMO dynamics. Full article

The resummation of Stieltjes series remains a key challenge in mathematical physics, especially when Padé approximants fail, as in the case of superfactorially divergent series. Weniger’s $\delta$-transformation, which incorporates a priori structural information on Stieltjes series, offers a superior framework with respect to Padé. In the present work, the following fundamental question is addressed: Is the $\delta$-transformation, once it is applied to a typical Stieltjes series, capable of correctly simulating the branch cut structure of the corresponding Stieltjes function? Here, it is proved that the intrinsic log-convexity of the Stieltjes moment sequence (guaranteed via the positivity of Hankel’s determinants) allows the necessary condition for $\delta$ to have all real poles to be satisfied. The same condition, however, is not sufficient to guarantee this. In attempting to bridge such a gap, we propose a mechanism rooted in the iterative action of a specific linear differential operator acting on a class of suitable auxiliary log-concave polynomials. To this end, we show that the denominator of the $\delta$-approximants can always be recast as a high-order derivative of a log-concave polynomial. Then, on invoking the Gauss–Lucas theorem, a consistent geometrical justification of the $\delta$ pole positioning is proposed. Through such an approach, the pole alignment along the negative real axis can be viewed as the result of the progressive restriction of the convex hull under differentiation. Since a fully rigorous proof of this conjecture remains an open challenge, in order to substantiate it, a comprehensive numerical investigation across an extensive catalog of Stieltjes series is proposed. Our results provide systematic evidence of the potential $\delta$-transformation ability to mimic the singularity structure of several target functions, including those involving superfactorial divergences. Full article

In this paper, we define new subclasses ${\mathcal{C}}_q(t,\lambda ,\delta ,n)$ and ${\mathcal{K}}_q(\eta ,t,\lambda ,\delta ,n)$ of analytic functions by using a Linear Multiplier q-differintegral operator with a generalized binomial series. In particular, we find the Hankel, Toeplitz determinant boundary values and Fekete–Szegö-type inequality for these defined classes. Full article

The study explores analytic, geometric and algebaraic properties of two subclasses of analytic functions: the class of Bounded Radius Rotation denoted by ${\mathcal{R}}_{\mathfrak{s}}{,}_{\varrho }(\mathcal{A},\mathcal{B},z)$, and the class of Bounded Boundary Rotation denoted by ${\mathcal{V}}_{\mathfrak{s}}{,}_{\varrho }(\mathcal{A},\mathcal{B},z)$, both associated with strongly Janowski type functions. In particular, we obtain upper bounds for the third-order Hankel determinant $|{\mathcal{H}}_{3,1}f\left(z\right)|$ and concentrate on functions displaying 2- and 3-fold symmetry. We also provide estimates for the initial logarithmic coefficients ${\eta }_1,{\eta }_2,{\eta }_3$ and the Zalcman functional $|t_3^2-t_5|$ for each class. These findings provide fresh insights into the behavior of generalized subclasses of univalent function. Full article

In this paper, we introduce a new class of analytic functions, denoted by $\mathfrak{S}(\nu ,{\phi }_{\vartheta ,e})$, and provide illustrative examples to elucidate its properties. This class generalizes the starlike and convex functions previously defined by Khatter et al. in relation to the exponential function. A significant contribution of this work is the derivation of sharp bounds for various coefficient-related problems within this class. The computational challenges involved in deriving these bounds were effectively addressed using Mathematica^TM codes. Additionally, figures illustrating the geometric properties and essential computations have been incorporated into the paper. Full article

In this paper, we introduce two novel subclasses of analytic functions, namely, starlike and convex functions of Ma–Minda-type, associated with a newly proposed domain. We set sharp bounds on the basic coefficients of these classes and provide sharp estimates of the second- and third-order Hankel determinants, demonstrating the power of our analytic approach, the clarity of its results, and its applicability even in unconventional domains. Full article

Let ${\mathcal{R}}_{LP}$ denote a newly introduced subclass of bounded turning functions. The primary aim of this study is to investigate the sharp bounds of the coefficients of $|d_2|,|d_3|,|d_4|,|d_5|$, as well as to establish precise estimates for the second- and third-order Hankel determinants $H_{2,1},H_{2,2},H_{2,3}$, and $H_{3,1}$ for functions belonging to this class. The coefficient bounds and Hankel determinant estimates derived herein are all shown to be sharp. Full article

In this paper, we introduce and investigate a new subclass ${\left({\mathcal{R}}_{\varsigma }^u\right)}^{\mathfrak{g}}\left(\varphi \right)$ of universally prestarlike generalized functions of order $\varsigma$, where $\varsigma \le 1$, associated with a shell-shaped region defined by $\Lambda =\mathrm{C}\setminus [1,\infty )$ for the present investigation, by utilizing the Srivastava–Owa fractional derivative of order $\delta$. Coefficient inequalities for $|{\mathfrak{a}}_2|$ and $|{\mathfrak{a}}_3|$ for functions belonging to the newly introduced class are obtained. Additionally, the Fekete–Szegö inequality is investigated for this class of functions. In order to enhance the coefficient studies for this class, the second Hankel determinant is also evaluated. Full article

This paper investigates a new subclass of bi-univalent analytic functions defined on the open unit disk in the complex plane, associated with the subordination to $1+\mathrm{s}\mathrm{i}\mathrm{n}z$. Coefficient bounds are obtained for the initial Taylor–Maclaurin coefficients, with a particular focus on the second- and third-order Hankel determinants. To illustrate the non-emptiness of the proposed class, we consider the function $\sqrt{1+tanhz}$, which maps the unit disk onto a bean-shaped domain. This function satisfies the required subordination condition and hence serves as an explicit member of the class. A graphical depiction of the image domain is provided to highlight its geometric characteristics. The results obtained in this work confirm that the class under study is non-trivial and possesses rich geometric structure, making it suitable for further development in the theory of geometric function classes and coefficient estimation problems. Full article

In this paper, we present a new integral operator that acts on a class of meromorphic functions on the punctured unit disc ${\mathbb{U}}^{*}$. This operator enables the definition of a new subclass of meromorphic univalent functions. We obtain sharp bounds for the Fekete–Szegö inequality and the second Hankel determinant for this class. The theoretical approach is based on differential subordination. Furthermore, we link these theoretical insights to applications in 2D electromagnetic field theory by outlining a physical framework in which the operator functions as a field transformation kernel. We show that the operator’s parameters correspond to physical analogs of field regularization and spectral redistribution, and we use subordination theory to simulate the design of vortex-free fields. The findings provide new insights into the interaction between geometric function theory and physical field modeling. Full article