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Axioms, Volume 15, Issue 9 (September 2026) – 56 articles

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14 pages, 328 KB  
Article
Local Convergence of the Gauss–Newton–Broyden Method for Solving Nonlinear Least Squares Problems
by Stepan Shakhno and Halyna Yarmola
Axioms 2026, 15(9), 682; https://doi.org/10.3390/axioms15090682 (registering DOI) - 13 Sep 2026
Abstract
The Gauss–Newton–Broyden method is proposed and investigated for solving a nonlinear least squares problem with operator decomposition. This method is obtained from the Gauss–Newton method by replacing the Jacobian matrix of a nonlinear operator with the sum of the derivative of the differentiable [...] Read more.
The Gauss–Newton–Broyden method is proposed and investigated for solving a nonlinear least squares problem with operator decomposition. This method is obtained from the Gauss–Newton method by replacing the Jacobian matrix of a nonlinear operator with the sum of the derivative of the differentiable part of the operator and the matrix computed by the Broyden update formula for the other part of the nonlinear vector function. A local convergence theorem for the proposed method, under the classical Lipschitz conditions and for problems with zero residual, is proved. The results of numerical experiments are also presented. Full article
(This article belongs to the Special Issue Advances in Nonlinear Dynamics: Theory and Application)
33 pages, 420 KB  
Article
Decay Rates of Solutions to the Cauchy Problem for p-System with Nonlinear and Space-Dependent Damping
by Fang He and Mina Jiang
Axioms 2026, 15(9), 681; https://doi.org/10.3390/axioms15090681 (registering DOI) - 12 Sep 2026
Abstract
In this paper, we study the Cauchy problem for the p-system with nonlinear and space-dependent damping. We focus on analyzing the asymptotic behavior and decay rates of solutions when the state constants for the specific volume are the same and the terminal [...] Read more.
In this paper, we study the Cauchy problem for the p-system with nonlinear and space-dependent damping. We focus on analyzing the asymptotic behavior and decay rates of solutions when the state constants for the specific volume are the same and the terminal states of velocity are zero: v+=v, u+=u=0. This is a new investigation of the combined effect of nonlinear and space-dependent damping. We explore what restrictions on the nonlinear damping are required to obtain the same asymptotic profile and decay rates as the results obtained in existing literature, and verify the conjecture that higher-order nonlinear damping does not affect the decay rates. The analysis is conducted via a priori estimates and energy methods. Full article
(This article belongs to the Section Mathematical Physics)
19 pages, 338 KB  
Article
A Three-Step Iterative Scheme for Nonexpansive Mappings: Convergence Analysis and Applications to Convex Optimization
by Fahad M. Alamrani, Nidal H. E. Eljaneid, Nifeen H. Altaweel, Mona Y. Alfefi, Shurooq B. Alblawie, Rana Ahmed Alshehri and Faizan Ahmad Khan
Axioms 2026, 15(9), 680; https://doi.org/10.3390/axioms15090680 - 11 Sep 2026
Abstract
This study focuses on a three-step iterative scheme, referred to as the NIP iteration, for the approximation of fixed points associated with nonexpansive mappings in uniformly convex Banach spaces. Weak convergence is established using Fejér monotonicity, asymptotic regularity and the demiclosedness principle. Strong [...] Read more.
This study focuses on a three-step iterative scheme, referred to as the NIP iteration, for the approximation of fixed points associated with nonexpansive mappings in uniformly convex Banach spaces. Weak convergence is established using Fejér monotonicity, asymptotic regularity and the demiclosedness principle. Strong convergence is proved under uniform convexity, compactness, and Condition (I) of Senter and Dotson. A numerical convergence and computational-cost comparison is developed numerically, showing that the NIP iteration performs better than the Ishikawa, S, Noor, Abbas–Nazir and SP schemes. Numerical experiments for nonlinear nonexpansive mappings validate the theoretical findings. An application to convex optimization via fixed point reformulation is also presented, illustrating the effectiveness of the method. Full article
(This article belongs to the Section Mathematical Analysis)
17 pages, 515 KB  
Article
On the Existence of Optimal (k(k − 1)s + 2, k, 1) Binary Cyclically Permutable Constant Weight Codes
by Tsonka Baicheva, Tsvetyana Yoveva and Svetlana Topalova
Axioms 2026, 15(9), 679; https://doi.org/10.3390/axioms15090679 (registering DOI) - 11 Sep 2026
Abstract
We derive necessary conditions for the existence of optimal (k(k1)s+2,k,1) binary cyclically permutable constant weight codes with length divisible by 2n, where n2. This [...] Read more.
We derive necessary conditions for the existence of optimal (k(k1)s+2,k,1) binary cyclically permutable constant weight codes with length divisible by 2n, where n2. This is achieved by counting in different ways the pairs of points in the corresponding partial cyclic design whose incidence matrix is equivalent to a matrix containing circulants of order v2m for 0m<n. Using a computer we check if these conditions hold for 3k200 and 1s10. We generalize the computer results by proving analytically that optimal (3k(k1)+2,k,1) binary cyclically permutable constant weight codes do not exist for k=16u+6. Full article
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34 pages, 1655 KB  
Article
Resolution-Adaptive Compact-Support Priors for Bayesian Wavelet Denoising: A Wendland–Semicircle Slab Mixture for Low-SNR Signal Recovery
by Nilotpal Sanyal
Axioms 2026, 15(9), 678; https://doi.org/10.3390/axioms15090678 - 11 Sep 2026
Abstract
We propose a resolution-adaptive Bayesian wavelet-denoising method for noisy one-dimensional signals. The main contribution is a spike-and-slab prior whose continuous slab is a mixture of a compactly supported Wendland-type polynomial kernel and the semicircle density, with data-adaptive, resolution-specific mixture weights, produced by a [...] Read more.
We propose a resolution-adaptive Bayesian wavelet-denoising method for noisy one-dimensional signals. The main contribution is a spike-and-slab prior whose continuous slab is a mixture of a compactly supported Wendland-type polynomial kernel and the semicircle density, with data-adaptive, resolution-specific mixture weights, produced by a low-dimensional empirical-Bayes trend. The Wendland component concentrates mass near zero and vanishes smoothly at the support boundary, whereas the semicircle component is more dispersed. This construction combines explicit sparsity and support control with an interpretable mechanism for adapting the shrinkage shape across resolutions. Under squared-error loss, we derive the posterior-mean estimator; establish key symmetry, boundedness, continuity, and limiting properties; define pointwise fixed-hyperparameter bias, variance, and risk; and develop an empirical-Bayes estimation procedure. The Wendland contribution has finite-sum expressions under a Laplace working likelihood, while the semicircle contribution is evaluated by stable one-dimensional integration. Simulations using the Bumps, Blocks, Doppler, and HeaviSine signals compare the proposed Gaussian- and Laplace-likelihood versions with universal thresholding, false-discovery-rate (FDR) thresholding, cross-validation (CV), Stein’s unbiased risk estimate (SURE), the Bayesian adaptive multiresolution shrinker (BAMS), and a nonlocal-prior (NLP)-based method. In the primary Gaussian-error simulation study, the Gaussian-likelihood version was the strongest non-NLP method in 24 of the 36 design cells, including 11 of the 12 low signal-to-noise ratio (SNR) cells, and had a substantially more favorable computational profile than the Laplace-likelihood version. Analysis of a seismic acceleration trace from the 2008 Chino Hills earthquake illustrates attenuation of rapid fluctuations and preservation of the dominant acceleration event under the chosen diagnostics. Using the processed channel-1 trace as surrogate truth, the corresponding semi-synthetic validation showed that WS–Gaussian improved on the noisy observation at lower and moderate SNRs but not at the highest SNR. Full article
(This article belongs to the Special Issue Computational Statistics and Its Applications, 2nd Edition)
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22 pages, 2036 KB  
Article
Numerical Interpretation and Graphical Visualization of Generalized Fuzzy Fractional Inequalities Through Different Convexities
by Mamoona Siddiq, Rana Safdar Ali, Hadia Noor and Dalal Alhwikem
Axioms 2026, 15(9), 677; https://doi.org/10.3390/axioms15090677 - 11 Sep 2026
Abstract
The generalization of convexities and fractional operators is a significant approach that not only refines the fractional inequalities but has also resolved many problems that are facing the non-integer family of calculus. In this paper, we introduce the class of modified exponential–trigonometric functions, [...] Read more.
The generalization of convexities and fractional operators is a significant approach that not only refines the fractional inequalities but has also resolved many problems that are facing the non-integer family of calculus. In this paper, we introduce the class of modified exponential–trigonometric functions, (p,s)-convex functions, and (s)-convex functions, and include them in a single framework of modified exponential trigonometric (p,s)-convex (MET-(p,s)-convex) functions. The present concept is generalized to the fuzzy-interval-valued case by means of Prabhakar fuzzy fractional integral operators. We obtain new Hermite–Hadamard- and trapezoid-type inequalities and their Hölder and power mean refinements. Lower and upper endpoint functions are utilized to prove the obtained results, and the results are also unified by fuzzy-order relation. The proposed class is a strict generalization of several convexity classes and fits some non-convex mappings not covered by the classical Hermite–Hadamard inequality. Moreover, the obtained inequalities offer computable upper and lower bounds to the uncertainty of Prabhakar fractional means. Theoretical results are illustrated by numerical examples and graphical illustrations, which show that the main advantage of the proposed framework is a wider class of admissible mappings rather than sharper numerical bounds. The classical Hermite–Hadamard inequality and several existing convexity-based inequalities are recovered as special cases of the results obtained here. Full article
(This article belongs to the Special Issue Theory and Application of Integral Inequalities, 3rd Edition)
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18 pages, 325 KB  
Article
Universal Approximation of Operators with Transformers and Neural Integral Operators
by Emanuele Zappala and Maryam Bagherian
Axioms 2026, 15(9), 676; https://doi.org/10.3390/axioms15090676 - 11 Sep 2026
Viewed by 64
Abstract
We study the universal approximation properties of transformers and neural integral operators for operators in Banach spaces. In particular, we show that the transformer architecture is a universal approximator of integral operators between Hölder spaces. Moreover, we show that a generalized version of [...] Read more.
We study the universal approximation properties of transformers and neural integral operators for operators in Banach spaces. In particular, we show that the transformer architecture is a universal approximator of integral operators between Hölder spaces. Moreover, we show that a generalized version of neural integral operators, based on the Gavurin integral, treats them as universal approximators of arbitrary operators between Banach spaces. Lastly, we show that a modified version of the transformer, which uses Leray–Schauder mappings, is a universal approximator of operators between arbitrary Banach spaces. Full article
(This article belongs to the Special Issue Functional Data Analysis and Its Application)
30 pages, 4136 KB  
Article
Systems in Chemotaxis: Mathematical Modeling, Invariant Analysis, Solitons and Numerical Solution
by Ali Raza, Alhussein Mohamed Alhussein Ahmed and Abdul Hamid Kara
Axioms 2026, 15(9), 675; https://doi.org/10.3390/axioms15090675 - 10 Sep 2026
Viewed by 130
Abstract
This paper investigates a nonlinear chemotaxis model involving diffusion and chemically directed transport. A detailed Lie symmetry analysis is carried out for different parameter cases, and the corresponding determining equations are derived explicitly to classify the admitted Lie point symmetries. Using the obtained [...] Read more.
This paper investigates a nonlinear chemotaxis model involving diffusion and chemically directed transport. A detailed Lie symmetry analysis is carried out for different parameter cases, and the corresponding determining equations are derived explicitly to classify the admitted Lie point symmetries. Using the obtained symmetry generators, several similarity reductions are constructed, including time-invariant, space-invariant, scaling, and traveling-wave reductions, with the reduced ordinary differential systems derived step by step. In particular, traveling-wave transformations reduce the governing PDE system to ordinary differential equations, from which several exact wave profiles are obtained, including multi-wave, breather-type, and kink-rational interaction solutions. The analytical structure and graphical behavior of these solutions are examined with the term soliton used only when the corresponding localization properties are satisfied. In addition, conservation-law approaches are employed to explore the structural properties of the model. Finally, the method of lines is used to obtain numerical approximations, allowing for a comparison with the analytical profiles and illustrating the influence of model parameters on the cell-density and chemical-concentration dynamics. Full article
(This article belongs to the Special Issue Applied Mathematics and Mathematical Modeling, 2nd Edition)
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63 pages, 657 KB  
Article
On the Incomplete Gamma and Biparametric Mittag-Leffler Functions
by Victor Kowalenko
Axioms 2026, 15(9), 674; https://doi.org/10.3390/axioms15090674 - 9 Sep 2026
Viewed by 100
Abstract
This paper presents new developments concerning the biparametric Mittag-Leffler function, Eα,β(z). First, numerous results are derived when the primary parameter, α, is set equal to unity. Many of these results are related to the incomplete [...] Read more.
This paper presents new developments concerning the biparametric Mittag-Leffler function, Eα,β(z). First, numerous results are derived when the primary parameter, α, is set equal to unity. Many of these results are related to the incomplete gamma function, Γ(a,z), or special cases of it, such as the error function. It is also found that the parameter a is related to the secondary parameter of the biparametric Mittag-Leffler function, β. More results are derived by considering other values, both fixed and algebraic, of the primary parameter. In particular, it is shown that, for rational values, the biparametric Mittag-Leffler function can be expressed as a finite sum of α=1 functions or incomplete gamma functions. Then, the asymptotic forms of the incomplete gamma function are made exact for z situated over the entire principal branch by the application of the regularization techniques, Borel summation and Mellin–Barnes regularization. Introducing the asymptotic forms for the incomplete gamma function into the newly derived results of the biparametric Mittag-Leffler function results in asymptotic forms that give exact values of the function, which, where possible, are checked with values from the MittagLefflerE instruction in Mathematica. Full article
(This article belongs to the Special Issue Recent Advances in Complex Analysis and Related Topics, 2nd Edition)
43 pages, 4356 KB  
Article
An Overview: Ordinary and Partial Differential Equations of Fractional Order on Examples in the Dynamics of Rheological Systems
by Katica R. (Stevanović) Hedrih
Axioms 2026, 15(9), 673; https://doi.org/10.3390/axioms15090673 - 8 Sep 2026
Viewed by 88
Abstract
An overview comparing ordinary and partial differential equations of fractional order, which arose as a new result of the author’s research and mathematical description of the differential constitutive relations of known and new models of fractional-type rheological materials, as well as the rheological [...] Read more.
An overview comparing ordinary and partial differential equations of fractional order, which arose as a new result of the author’s research and mathematical description of the differential constitutive relations of known and new models of fractional-type rheological materials, as well as the rheological longitudinal dynamics of these materials, is given. Systems of differential equations of fractional order are also presented, which describe the dynamics of rheological models of discrete dynamic systems such as rheological oscillators or creepers. Systems of fractional-order differential equations, dynamics of rheological models of discrete dynamic systems in which standard light coupling sets of the fractional-type Kelvin–Voight/Kelvin–Voight–Faraday model or the fractional-type Maxwell/Maxwell–Faraday model with piezoelectric effects are incorporated, are also presented. The methodology of approximate analytical solutions of some of the presented ordinary and partial differential equations of fractional order will also be indicated. Full article
(This article belongs to the Special Issue Fractional Differential Equation and Its Applications, 2nd Edition)
22 pages, 10095 KB  
Article
Modeling Saudi Price Index Using a New Bivariate Family of Distributions
by Jumanah Ahmed Darwish
Axioms 2026, 15(9), 672; https://doi.org/10.3390/axioms15090672 - 8 Sep 2026
Viewed by 73
Abstract
The price index of daily commodities is an important indicator of inflation in a country. Adequate modeling of the price index is useful for efficient economic decision-making. Since the exact modeling of the price index is impossible, probabilistic modeling is a suitable alternative [...] Read more.
The price index of daily commodities is an important indicator of inflation in a country. Adequate modeling of the price index is useful for efficient economic decision-making. Since the exact modeling of the price index is impossible, probabilistic modeling is a suitable alternative for this. The change in the price index of various commodities at different time points is usually dependent, and hence joint modeling is a suitable solution. In this paper, a new family of distributions is proposed for joint modeling of the price index of various Saudi commodities at two different time points and is named as Darwish Bivariate Family of Distributions (DBFDs). Some necessary properties of the family are presented, and some dependence measures are also computed. Conditional distributions for the proposed family are investigated alongside the method for random data generation from any member of the proposed family. The parameter estimation for the proposed family is discussed in general. A specific member of the family, namely the Darwish Bivariate Log-logistic (DBLL) distribution, is studied in detail. Some important properties of the DBLL distribution are presented. The DBLL distribution is used to model the price index of various Saudi commodities. It is found that the proposed DBLL distribution provides a better fit to model the price index in comparison with the other models used in the study. Full article
(This article belongs to the Special Issue Advances in Mathematical Statistics and Data Analysis)
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43 pages, 9569 KB  
Article
Measuring Urban Economic Performance in G7 Countries Through a Novel Grey-Based Multi-Criteria Framework
by Sarfaraz Hashemkhani Zolfani, Ahmet Şengönül, Şerife Merve Koşaroğlu, Berrak Tekgün and Özcan Işık
Axioms 2026, 15(9), 671; https://doi.org/10.3390/axioms15090671 - 8 Sep 2026
Viewed by 195
Abstract
Cities are the main sites of production, employment, and capital accumulation in advanced economies, which places urban economic performance at the centre of economic policy and urban governance. This work develops an integrated grey-based multi-criteria approach for assessing that performance and applies it [...] Read more.
Cities are the main sites of production, employment, and capital accumulation in advanced economies, which places urban economic performance at the centre of economic policy and urban governance. This work develops an integrated grey-based multi-criteria approach for assessing that performance and applies it to the sixteen G7 cities covered by the Global Power City Index (GPCI). Criterion weights are obtained with Grey RANCOM (G-RANCOM), which converts the ordinal rankings of a five-member expert panel into interval weights, and the cities are ranked with Grey MUNRA (G-MUNRA), which aggregates linear, vector, and non-linear normalization. Each performance entry is an interval bounded by the minimum and the maximum annual score observed in the GPCI Economy function over 2021–2025. Market size, economic vitality, and business environment emerge as the most influential criteria, and New York, London, and Tokyo occupy the highest positions, while Osaka, Milan, and Fukuoka occupy the last three. Robustness is tested via scenario analyses on the model parameters and through a global analysis of 100,000 replications in which all of them vary jointly. New York holds the first position in 74% of the replications and the three lowest positions are unchanged in 87%, whereas cities in adjacent middle positions are not separated reliably. Rankings produced by five established grey approaches, by crisp and fuzzy counterparts, and by the published GPCI Economy rankings agree with the reported ordering, with Spearman correlations between 0.92 and 1.00. The framework offers urban policymakers a transparent benchmarking tool for evidence-based competitiveness strategies. Full article
(This article belongs to the Special Issue 15th Anniversary of Axioms: Logic)
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13 pages, 273 KB  
Article
Conditional Double Integral Transforms with Related Topics on Product Abstract Wiener Space
by Hyun Soo Chung
Axioms 2026, 15(9), 670; https://doi.org/10.3390/axioms15090670 - 7 Sep 2026
Viewed by 106
Abstract
In this paper, we introduce a conditional double integral transform and a conditional double convolution product for a broad class of functionals defined on product abstract Wiener space. We first establish the existence of the conditional double integral transform, the conditional double convolution [...] Read more.
In this paper, we introduce a conditional double integral transform and a conditional double convolution product for a broad class of functionals defined on product abstract Wiener space. We first establish the existence of the conditional double integral transform, the conditional double convolution product, and the first variation of the associated functionals under appropriate conditions. We then investigate their fundamental properties and derive several relationships among these three concepts, thereby extending the corresponding theory of integral transforms and convolution products on Wiener space. Furthermore, by combining these results, we obtain a unified analytical framework that clarifies the interplay between the conditional double integral transform, the conditional double convolution product, and the first variation. These relationships lead to several new identities and provide a systematic approach to the analysis of functionals on product abstract Wiener space. Finally, we present several observations and illustrative consequences concerning the conditional double integral transform and the conditional double convolution product, which demonstrate the applicability of the proposed framework and suggest directions for further research in Wiener analysis and related areas of mathematical physics. Full article
12 pages, 265 KB  
Article
The Center Problem for Analytic Maps with Mixed Even-Degree Terms
by Renato Petek, Brigita Ferčec, Wilker Fernandes and Matej Mencinger
Axioms 2026, 15(9), 669; https://doi.org/10.3390/axioms15090669 - 7 Sep 2026
Viewed by 129
Abstract
We investigate the center problem for analytic maps implicitly defined by algebraic equations of the form [...] Read more.
We investigate the center problem for analytic maps implicitly defined by algebraic equations of the form F(x,y)=x+y+i+k=2nαi,kxiyk=0. Previous studies of homogeneous analytic maps of even degree and of mixed terms of degrees 2 and 4 revealed two recurring algebraic families characterizing the existence of a center at the origin: mirror-symmetry conditions and alternating-sum conditions. In this paper, we resolve the next open case involving mixed terms of degrees 2 and 6 and show that the same algebraic structure extends to mixed terms of degrees 2 and arbitrary even number. Using an approach based on the involutive identity f(f(x))=x, we prove that these two families of algebraic conditions completely characterize the existence of a center at the origin. The proof combines algebraic and structural arguments and avoids the use of explicit higher-order focus quantity computations in the general case. Full article
(This article belongs to the Special Issue Advances in Differential Equations and Its Applications, 2nd Edition)
1 pages, 147 KB  
Correction
Correction: Jerby, Y. On the Approximation of the Hardy Z-Function via High-Order Sections. Axioms 2024, 13, 577
by Yochay Jerby
Axioms 2026, 15(9), 668; https://doi.org/10.3390/axioms15090668 - 7 Sep 2026
Viewed by 86
Abstract
There were errors in the original publication [...] Full article
(This article belongs to the Section Mathematical Analysis)
22 pages, 368 KB  
Article
Entire Functions of Several Variables: Wiman–Valiron-Type Results Without Exceptional Sets
by Oleh Skaskiv, Andriy Bandura, Tetiana Salo, Sviatoslav Dubei and Liudmyla Kryshtopa
Axioms 2026, 15(9), 667; https://doi.org/10.3390/axioms15090667 - 6 Sep 2026
Viewed by 133
Abstract
This article is devoted to establishing analogs of the main theorems of the Wiman–Valiron theory on asymptotic relations for entire functions of several complex variables that are satisfied without exceptional sets when the complex space is exhausted by a system of multiple-circular domains [...] Read more.
This article is devoted to establishing analogs of the main theorems of the Wiman–Valiron theory on asymptotic relations for entire functions of several complex variables that are satisfied without exceptional sets when the complex space is exhausted by a system of multiple-circular domains or by a system of A-like polylinear domains. These results concern: (i) analogs of the asymptotic equality of the logarithms of the maximum modulus of an entire function on the boundary of multiple-circular domains of exhaustion and the corresponding maximal term; (ii) a statement describing the behavior of the entire function F(z) of several complex variables z=(z1,,zp) in the vicinity of the point w, where the value of F(w) is close to the supremum of its modulus on the boundary of polylinear domains; (iii) the so-called fundamental relation of the Wiman–Valiron theory, which establishes the asymptotic behavior of directional derivatives for a given fixed direction of the vector A, which specifies the direction of space exhaustion. Full article
(This article belongs to the Special Issue Theory of Functions and Applications, 3rd Edition)
15 pages, 2104 KB  
Article
Statistical Invariants for Classification on Tiny Datasets
by Carlo Ruiz-Castillo and Gustavo Cruz-Pacheco
Axioms 2026, 15(9), 666; https://doi.org/10.3390/axioms15090666 - 6 Sep 2026
Viewed by 185
Abstract
We investigate the influence of statistical invariants for classification problems on tiny datasets. We present a review of current state-of-the-art methods for classification, with a brief discussion of the differences and trade-offs between the proposed method and existing classifiers. Then, we lay out [...] Read more.
We investigate the influence of statistical invariants for classification problems on tiny datasets. We present a review of current state-of-the-art methods for classification, with a brief discussion of the differences and trade-offs between the proposed method and existing classifiers. Then, we lay out the philosophical and mathematical foundations of the statistical theory of learning, incorporating the discovery of statistical invariants. We derive algorithmic implementations for binary, multiclass, and multilabel classification alongside technical details and recommendations for practitioners. We demonstrate the efficacy of the proposed algorithm through comparative studies against state-of-the-art AutoML frameworks on a benchmark suite. Full article
(This article belongs to the Special Issue Advances in Statistical Simulation and Computing, 2nd Edition)
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26 pages, 375 KB  
Article
Riemannian vs. Lorentzian Geometry: A Multilevel Comparison
by Giovanni Calvaruso and Maria Letizia Russo
Axioms 2026, 15(9), 665; https://doi.org/10.3390/axioms15090665 - 5 Sep 2026
Viewed by 133
Abstract
We present a comparative exposition of Riemannian and Lorentzian geometries, organized through successive levels of increasing structure. Beginning with scalar products on vector spaces, we proceed through smooth manifolds, left-invariant metrics on Lie groups, homogeneous spaces and contact metric geometry. At each level, [...] Read more.
We present a comparative exposition of Riemannian and Lorentzian geometries, organized through successive levels of increasing structure. Beginning with scalar products on vector spaces, we proceed through smooth manifolds, left-invariant metrics on Lie groups, homogeneous spaces and contact metric geometry. At each level, we emphasize which notions and results survive the transition from positive-definite to Lorentzian signature, which ones fail, and the mechanisms responsible for these differences. Recurring themes include: the emergence of causal structures, the loss of diagonalizability of self-adjoint operators, the failure of the equivalence between metric and geodesic completeness, and the topological obstruction to the existence of Lorentzian metrics on compact manifolds. Particular attention is devoted to the classification of three-dimensional homogeneous spaces, including Bianchi–Cartan–Vranceanu spaces and their Lorentzian counterparts, and to the contact metric setting, where an additional geometric structure restores a correspondence between the Riemannian and Lorentzian theories. Full article
(This article belongs to the Special Issue 15th Anniversary of Axioms: Geometry and Topology)
41 pages, 570 KB  
Article
An Explicit Closed Form for a Half-Integer 3F2(1) Family with Negative Integral Parameter Differences, via Odd Harmonic Sums
by Abdelhamid Zaidi
Axioms 2026, 15(9), 664; https://doi.org/10.3390/axioms15090664 - 4 Sep 2026
Viewed by 136
Abstract
We study the half-integer family [...] Read more.
We study the half-integer family F(n,p)=F232n+12,1,2p12;2n+52,2p+12;1. Although this family belongs to the Karlsson–Minton class of F23(1) series with negative integral parameter differences, the most directly relevant symmetric formula of Shpot and Srivastava becomes singular at the free numerator parameter a=1 (here a denotes the first numerator parameter of the Shpot–Srivastava reduction formula, the value of which controls the Beta factors in their evaluation). We show that this apparent singularity is removable and identify its finite value with the independently derived closed form. First, Euler’s integral representation and a recurrence for Jm,n(x)=01v2m(1xv2)ndv yield a closed form for F122n+12,1;2n+52;x as a polynomial in (1x) plus arctanh(x)/x. Rainville’s integral formula then reduces F(n,p) to a rational part and a finite rational linear combination of odd harmonic sums Hrodd=j=1r(2j1)1. For all integers n0 and pn+3, this proves F(n,p)Q. The threshold is sharp: at the adjacent boundary p=n+2 we obtain F(n,n+2)=Rn+Cnπ2 with Rn,CnQ and Cn0, so rationality fails. We also prove, by analyticity and the independently derived formula, that the a1 limit of the Shpot–Srivastava representation equals the present closed form. For computation, the exact assembly uses O(n+p) arithmetic operations under the unit-cost model, while a direct fixed-precision evaluation is ill-conditioned for large n. A stable series/closed-form hybrid for the F12 factor combined with adaptive positive-kernel Gauss–Jacobi quadrature gives relative errors at the machine-precision scale over the tested range up to n=64. Full article
(This article belongs to the Special Issue Recent Advances in Special Functions and Applications, 2nd Edition)
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14 pages, 292 KB  
Article
Construction of Lacunary Sequence Spaces via Modulus Function and Nörlund-Mean of Order α
by Hong-Wei Wang, Priyanka Sharma, Kuldip Raj, Sunil K. Sharma and Qing-Bo Cai
Axioms 2026, 15(9), 663; https://doi.org/10.3390/axioms15090663 - 4 Sep 2026
Viewed by 126
Abstract
In this work, we introduce new classes of lacunary sequence spaces based on Nörlund-type means, a sequence of modulus functions and the order parameter 0<α1. The main novelty is the incorporation of these components into a weighted Nörlund-lacunary [...] Read more.
In this work, we introduce new classes of lacunary sequence spaces based on Nörlund-type means, a sequence of modulus functions and the order parameter 0<α1. The main novelty is the incorporation of these components into a weighted Nörlund-lacunary framework. We establish inclusion and equivalence relations with classical Nörlund-type and lacunary sequence spaces under explicit conditions on the weight and lacunary sequences. We further characterize weighted lacunary statistical convergence of order α and investigate its relationships with the corresponding convergence spaces. Finally, we prove the completeness and topological properties of the resulting paranormed sequence spaces. These results extend existing frameworks for lacunary and Nörlund-type sequence spaces. Full article
(This article belongs to the Section Mathematical Analysis)
22 pages, 246 KB  
Article
Variational Inequalities Induced by Set-Valued Mappings
by Alexander J. Zaslavski
Axioms 2026, 15(9), 662; https://doi.org/10.3390/axioms15090662 - 4 Sep 2026
Viewed by 122
Abstract
In an infinite-dimensional Hilbert space, we investigate a method for finding a solution of a variational inequality induced by an inverse strongly monotone set-valued mapping. Our results are established in the presence of summable and nonsummable computational errors. We show that our algorithm [...] Read more.
In an infinite-dimensional Hilbert space, we investigate a method for finding a solution of a variational inequality induced by an inverse strongly monotone set-valued mapping. Our results are established in the presence of summable and nonsummable computational errors. We show that our algorithm generates a good approximate solution, if the sequence of computational errors is bounded from above by a constant. Full article
(This article belongs to the Section Mathematical Analysis)
13 pages, 262 KB  
Article
An Integrable Nonlinear Schrödinger System with Symmetric Matrix Potentials and Its Binary Darboux Transformations
by Wen-Xiu Ma
Axioms 2026, 15(9), 661; https://doi.org/10.3390/axioms15090661 - 3 Sep 2026
Viewed by 154
Abstract
This study aims to propose a class of binary Darboux transformations for an integrable nonlinear Schrödinger system with two symmetric matrix potentials. The associated Lax pairs of AKNS type ensure the existence of these binary Darboux transformations, whose explicit single-step applications yield soliton [...] Read more.
This study aims to propose a class of binary Darboux transformations for an integrable nonlinear Schrödinger system with two symmetric matrix potentials. The associated Lax pairs of AKNS type ensure the existence of these binary Darboux transformations, whose explicit single-step applications yield soliton solutions. Notably, the M-matrix appearing in the formulation of the binary Darboux transformations must be constructed within an extended framework, allowing for cases where eigenvalues coincide with adjoint eigenvalues, thereby encompassing generalized Darboux transformations as well. Full article
(This article belongs to the Section Mathematical Physics)
34 pages, 625 KB  
Article
False Chebyshev Primes: Prime-Phase Non-Equidistribution and a Weighted Local-Time Law
by Michel Planat
Axioms 2026, 15(9), 660; https://doi.org/10.3390/axioms15090660 - 2 Sep 2026
Viewed by 181
Abstract
Let ψ be the Chebyshev prime-counting function and π(x) the number of primes up to x. The Chebyshev-prime condition [...] Read more.
Let ψ be the Chebyshev prime-counting function and π(x) the number of primes up to x. The Chebyshev-prime condition K(p)=li(ψ(p))li(ψ(p1))<1 is not equivalent to the sign rule ψ(p)p>0. We prove that its leading threshold is the midpoint correction ψ(p)p>12logp, with an explicit higher-order boundary, and define false Chebyshev primes through the resulting transition layer. Our main unconditional theorem shows that ordinary prime counting does not equidistribute logarithmic prime phases: for every nonzero integer combination τ of nontrivial zeta-zero ordinates, π(x)1pxpiτ=xiτ/(1+iτ)+o(1). By contrast, the logarithmically uniform weight logp/p restores finite-dimensional Haar equidistribution for rationally independent ordinates. This dichotomy motivates the weighted local-time statistic L+(x)=2p1/2, summed over the layer primes px. We show that the layer is exactly the one-sided slab T(p)<B(logp)<0 of the midpoint-centered field B, where T(p)=logp/(2p), so that L+ is a bona fide occupation density. Assuming the Riemann hypothesis, linear independence, and a shrinking-window local limit hypothesis that we isolate as a separate open problem, we prove the one-directional Cesàro law L+(x)/logxfB(0), where fB(0) is the value at the origin of the limiting density of B (numerically fB(0)1.828). Independently, we prove shrinking-target occupation laws via coarea formulas: unconditionally for fixed windows, including for the finite zeta-derived field itself, and under uniform transversality for the diagonal window. The remaining obstacles are tangential crossings of that field and transfer to the prime-sampled diagonal window. Full article
(This article belongs to the Section Algebra and Number Theory)
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17 pages, 711 KB  
Article
Scale Mixture of Akash Distribution with Applications to Income Data
by Neveka M. Olmos, Luis Firinguetti-Limone, Diego I. Gallardo, Osvaldo Venegas and Héctor W. Gómez
Axioms 2026, 15(9), 659; https://doi.org/10.3390/axioms15090659 - 2 Sep 2026
Viewed by 168
Abstract
In this paper, the scale mixture of Akash (SMAK) distribution is introduced. This new distribution results from a scale mixture of the Akash distribution and the exponential distribution. The SMAK distribution is an alternative to two-parameter distributions with a heavy right tail. We [...] Read more.
In this paper, the scale mixture of Akash (SMAK) distribution is introduced. This new distribution results from a scale mixture of the Akash distribution and the exponential distribution. The SMAK distribution is an alternative to two-parameter distributions with a heavy right tail. We study its representation, some basic properties, and maximum likelihood inference. We carry out three applications with real data, in which the SMAK distribution exhibits better performance than other distributions. Full article
(This article belongs to the Special Issue Advances in the Theory and Applications of Statistical Distributions)
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21 pages, 481 KB  
Article
Simultaneous Confidence Intervals for Odds Ratios in Bilateral Correlated Data Under Equal Correlation Coefficient Model
by Zhaoqi Zhang and Chang-Xing Ma
Axioms 2026, 15(9), 658; https://doi.org/10.3390/axioms15090658 - 1 Sep 2026
Viewed by 190
Abstract
Bilateral data arising from paired organs or limbs within the same subject frequently occur in clinical trials and biomedical research. Neglecting the intraclass correlation inherent in such data can lead to inaccurate variance estimation and invalid statistical inference. Donner’s equal correlation coefficient model [...] Read more.
Bilateral data arising from paired organs or limbs within the same subject frequently occur in clinical trials and biomedical research. Neglecting the intraclass correlation inherent in such data can lead to inaccurate variance estimation and invalid statistical inference. Donner’s equal correlation coefficient model addresses this issue by assuming a single, common intraclass correlation coefficient across all individuals to characterize the dependence between paired observations from the same subject. Although prior research under this model has developed asymptotic testing procedures and confidence interval approaches for two-group comparisons of proportions, simultaneous confidence intervals for the odds ratio have not been thoroughly investigated. This article derives nine asymptotic simultaneous confidence intervals for the odds ratio and evaluates their performance through extensive Monte Carlo simulations, focusing on the empirical coverage probability and mean interval width. A real-world example is presented to illustrate the practical application of the proposed methods. Full article
(This article belongs to the Special Issue New Perspectives in Mathematical Statistics, 2nd Edition)
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23 pages, 429 KB  
Article
Some Classes of Bi-Starlike and Bi-Convex Functions Associated with the Poisson-Charlier Polynomials
by Hari M. Srivastava, Areej Alomar and Maslina Darus
Axioms 2026, 15(9), 657; https://doi.org/10.3390/axioms15090657 - 1 Sep 2026
Viewed by 199
Abstract
Motivated by the interplay between discrete orthogonal polynomials and geometric function theory, we introduce and investigate some new Ma-Minda-type subclasses of bi-univalent functions generated by the Poisson-Charlier polynomials through their following analytic generating function: [...] Read more.
Motivated by the interplay between discrete orthogonal polynomials and geometric function theory, we introduce and investigate some new Ma-Minda-type subclasses of bi-univalent functions generated by the Poisson-Charlier polynomials through their following analytic generating function: Ea(x,z)=(1+z)xeaz(|z|<1). Within the classical class Σ of analytic and bi-univalent functions, we first define the Poisson-Charlier-generated bi-starlike and bi-convex families via the subordination relations involving Ea(x,·) for both a function f and its inverse f1. By combining the Carathéodory representation with the series expansion of Ea(x,z) and the Lagrange inversion formula for f1, we derive coefficient estimates for the initial Taylor-Maclaurin coefficients a2 and a3 of functions in the starlike class Σ𝒮*E(a,x) and in the convex class Σ𝒦E(a,x). In addition, we obtain corresponding Fekete-Szegö type inequalities of the form a3μa22 for a real parameter μ in both settings, which are expressed explicitly in terms of the parameters a and x of the Poisson-Charlier framework. To the best of our knowledge, these Poisson-Charlier-generated bi-starlike and bi-convex classes have not previously been investigated, so the resulting coefficient and Fekete-Szegö estimates constitute a distinct contribution rather than direct special cases of previously studied Ma-Minda families. Full article
(This article belongs to the Special Issue Mathematical Analysis and Applications, 5th Edition)
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45 pages, 739 KB  
Article
A Comparison of Shiryaev–Roberts and Cumulative Sum Procedures for Bivariate ZIP Process Monitoring
by Xiaoling Bo, Jiujun Zhang, Peile Chen, Zixin Wang and Dan Yu
Axioms 2026, 15(9), 656; https://doi.org/10.3390/axioms15090656 - 1 Sep 2026
Viewed by 155
Abstract
The Zero-inflated Poisson (ZIP) model has been widely adopted in quality control for near-zero-defect processes with sporadic nonconformities, while prior research predominantly focused on univariate ZIP processes for single defect types, modern high-precision manufacturing environments often involve two or more correlated defect categories. [...] Read more.
The Zero-inflated Poisson (ZIP) model has been widely adopted in quality control for near-zero-defect processes with sporadic nonconformities, while prior research predominantly focused on univariate ZIP processes for single defect types, modern high-precision manufacturing environments often involve two or more correlated defect categories. This paper proposes a Shiryaev–Roberts (SR) control chart for detecting parameter shifts in bivariate ZIP processes and compares its performance with the existing cumulative sum (CUSUM) chart under both zero-state and steady-state scenarios. Through Monte Carlo simulations, we establish the upper control limits (h) for both schemes while maintaining an identical in-control average run length (ARL) to ensure fair comparisons. Numerical simulations demonstrate that the SR chart exhibits superior out-of-control ARL performance compared to the CUSUM chart under steady-state conditions for detecting small to moderate shifts. The proposed methodology is further validated through a case study in LED packaging, highlighting its practicality in advanced manufacturing quality assurance. Full article
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15 pages, 359 KB  
Article
An Index Refined Winding Pair Polynomial for Planar Knotoids
by Liang Liang and Liyuan Ma
Axioms 2026, 15(9), 655; https://doi.org/10.3390/axioms15090655 - 1 Sep 2026
Viewed by 119
Abstract
Planar knotoids contain endpoint position information because the forbidden endpoint moves prevent the leg and the head from passing across arcs. Existing polynomial invariants based on Gauss diagrams and winding data record important parts of this information, but they may separate endpoint winding [...] Read more.
Planar knotoids contain endpoint position information because the forbidden endpoint moves prevent the leg and the head from passing across arcs. Existing polynomial invariants based on Gauss diagrams and winding data record important parts of this information, but they may separate endpoint winding data from affine index data or combine winding contributions only after summation. We introduce an index refined winding pair polynomial in three variables for oriented planar knotoids. At each crossing, the invariant records the ordered winding pair of the crossing lobe together with the affine index weight of the same crossing. We prove invariance under planar knotoid equivalence, derive formulas for orientation reversal, mirror image and planar product, and show that the invariant is a Vassiliev invariant of degree one. We also obtain lower bounds for crossing number, Gordian distance and unknotting number from a nonconstant coefficient norm. Finally, explicit computations show that the winding signed sum polynomial and the affine index polynomial, even when considered together, do not determine the new invariant. Full article
(This article belongs to the Section Geometry and Topology)
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38 pages, 1017 KB  
Article
Stochastic Wolbachia Dynamics: Persistence, Invariant Measures, and Probability-Based Release Strategies
by Eddy A. Kwessi
Axioms 2026, 15(9), 654; https://doi.org/10.3390/axioms15090654 - 1 Sep 2026
Viewed by 223
Abstract
We develop a stochastic discrete-time framework for Wolbachia invasion in mosquito populations under environmental variability. Starting from a deterministic frequency-dependent difference equation with an Allee-type threshold, we consider the random iteration Xn+1=FΘn(Xn) [...] Read more.
We develop a stochastic discrete-time framework for Wolbachia invasion in mosquito populations under environmental variability. Starting from a deterministic frequency-dependent difference equation with an Allee-type threshold, we consider the random iteration Xn+1=FΘn(Xn), where Θn represents fluctuations in fitness cost, cytoplasmic incompatibility, and maternal transmission. We establish existence, uniqueness, positivity, forward invariance of [0,1], continuity, and pathwise order preservation, and formulate the model as a random dynamical system. Under independent environmental forcing, the process is Markovian; the associated Markov operator is Feller, and compactness of the state space implies the existence of invariant probability measures. Local behavior near extinction is characterized by the stochastic Lyapunov exponent λ=Elog(1M)(1Sf), with λ<0 yielding local exponential stability of the Wolbachia-free state. We further introduce finite-horizon establishment probabilities and probability-based release thresholds, whose monotonicity follows from the pathwise comparison principle. Numerical simulations show how the magnitude, source, and dependence structure of environmental variability affect invasion probabilities and release requirements. The framework combines nonlinear difference equations, random dynamical systems, Markov operators, invariant measure theory, and stochastic stability in a unified analysis of threshold-dependent Wolbachia invasion. Full article
(This article belongs to the Special Issue Numerical Analysis and Applied Mathematics, 2nd Edition)
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24 pages, 498 KB  
Article
Bayesian Additive Regression Trees for Circular Data: A Machine Learning Framework
by Talal Kurdi and Saralees Nadarajah
Axioms 2026, 15(9), 653; https://doi.org/10.3390/axioms15090653 - 31 Aug 2026
Viewed by 231
Abstract
Circular data arise in a wide range of scientific fields, including meteorology, medicine, biology, and neuroscience, yet existing regression methods for such data are largely restricted to parametric generalized linear models or tree-based methods that impose distributional assumptions on the circular response. In [...] Read more.
Circular data arise in a wide range of scientific fields, including meteorology, medicine, biology, and neuroscience, yet existing regression methods for such data are largely restricted to parametric generalized linear models or tree-based methods that impose distributional assumptions on the circular response. In this paper, we propose a family of Bayesian Additive Regression Tree (BART) methods for regression with circular data, covering three cases: Circular–Circular BART (CCBART), where both the response and the covariates are circular; Circular–Linear BART (CLBART), where the response is circular and the covariates are linear; and Linear–Circular BART (LCBART), where the response is linear and the covariates are circular. The proposed methods adopt a projection approach, decomposing circular variables into their sine and cosine components, fitting separate BART models on these projections, and recovering circular predictions via the two-argument arctangent function. This avoids specifying a von Mises or wrapped normal likelihood directly for the circular response, though it does not avoid all distributional assumptions: BART assumes flexible Euclidean regression models, with Gaussian errors, for the projected sine and cosine components. The approach retains the full inferential power of BART, including posterior uncertainty quantification, automatic variable selection, and the ability to capture nonlinear effects and interactions without pre-specification. An extensive simulation study demonstrates that the proposed methods are highly competitive with random forest benchmarks and consistently outperform linear model benchmarks, with the clearest and most consistent advantage over random forests emerging at high noise levels and in the Linear–Circular case, where LCBART achieves up to 34% lower RMSE than projected random forests. Applications to wind direction forecasting and human motor resonance data further illustrate the practical utility of the proposed methods. Full article
(This article belongs to the Section Mathematical Analysis)
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