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AppliedMath, Volume 5, Issue 3 (September 2025) – 33 articles

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16 pages, 301 KiB  
Article
Solutions of Nonlinear Differential and Integral Equations via Optimality Results Involving Proximal Mappings
by Sonam, Deb Sarkar, Purvee Bhardwaj, Satyendra Narayan and Ramakant Bhardwaj
AppliedMath 2025, 5(3), 108; https://doi.org/10.3390/appliedmath5030108 - 22 Aug 2025
Abstract
This research paper delves into the application of optimality results in orthogonal fuzzy metric spaces to demonstrate the existence and uniqueness of solutions of nonlinear differential equations with boundary conditions and nonlinear integral equations, emphasizing the importance of orthogonal fuzzy metric spaces in [...] Read more.
This research paper delves into the application of optimality results in orthogonal fuzzy metric spaces to demonstrate the existence and uniqueness of solutions of nonlinear differential equations with boundary conditions and nonlinear integral equations, emphasizing the importance of orthogonal fuzzy metric spaces in extending fixed-point theory. Through introducing this innovative concept, the study provides a theoretical framework for analyzing mappings in diverse scenarios. In this study, we introduce the concept of best proximity point (BPP) within the framework of orthogonal fuzzy metric spaces by employing orthogonal fuzzy proximal contractive mappings. Moreover, this research explores the implications of the established results, considering both self-mappings and non-self mappings that share the same parameter set. Additionally, some examples are provided to illustrate the practical relevance of the proven results and consequences in various mathematical contexts. The findings of this study can open up avenues for further exploration and application in solving real-world problems. Full article
19 pages, 475 KiB  
Article
Modeling and Optimal Control of Liquidity Risk Contagion in the Banking System with Delayed Status and Control Variables
by Hamza Mourad, Said Fahim and Mohamed Lahby
AppliedMath 2025, 5(3), 107; https://doi.org/10.3390/appliedmath5030107 - 15 Aug 2025
Viewed by 185
Abstract
The application of contagion risk spread modeling within the banking sector is a relatively recent development, emerging as a response to the persistent threat of liquidity risk that has affected financial institutions globally. Liquidity risk is recognized as one of the most destructive [...] Read more.
The application of contagion risk spread modeling within the banking sector is a relatively recent development, emerging as a response to the persistent threat of liquidity risk that has affected financial institutions globally. Liquidity risk is recognized as one of the most destructive financial threats to banks, capable of causing severe and irreparable damage if overlooked or underestimated. This study aims to identify the most effective control strategy for managing financial contagion using a Susceptible–Infected–Recovered (SIR) epidemic model, incorporating time delays in both state and control variables. The proposed strategy seeks to maximize the number of resilient (vulnerable) banks while minimizing the number of infected institutions at risk of bankruptcy. Our goal is to formulate intervention policies that can curtail the propagation of financial contagion and mitigate associated systemic risks. Our model remains a simplification of reality. It does not account for strategic interactions between banks (e.g., panic reactions, network coordination), nor for adaptive regulatory mechanisms. The integration of these aspects will be the subject of future work. We establish the existence of an optimal control strategy and apply Pontryagin’s Maximum Principle to characterize and analyze the control dynamics. To numerically solve the control system, we employ a discretization approach based on forward and backward finite difference approximations. Despite the model’s simplifications, it captures key dynamics relevant to major European banks. Simulations performed using Python 3.12 yield significant results across three distinct scenarios. Notably, in the most severe case (α3=1.0), the optimal control strategy reduces bankruptcies from 25% to nearly 0% in Spain, and from 12.5% to 0% in France and Germany, demonstrating the effectiveness of timely intervention in containing financial contagion. Full article
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15 pages, 1886 KiB  
Article
On Unit-Burr Distorted Copulas
by Fadal Abdullah A. Aldhufairi and Jungsywan H. Sepanski
AppliedMath 2025, 5(3), 106; https://doi.org/10.3390/appliedmath5030106 - 14 Aug 2025
Viewed by 123
Abstract
This paper introduces a new unit-Burr distortion function constructed via a transformation of the Burr random variable. The distortion can be applied to existing base copulas to create new copula families. The relationships of tail dependence coefficients and tail orders between the base [...] Read more.
This paper introduces a new unit-Burr distortion function constructed via a transformation of the Burr random variable. The distortion can be applied to existing base copulas to create new copula families. The relationships of tail dependence coefficients and tail orders between the base bivariate copula and the unit-Burr distorted copula are derived. The unit-Burr distortion-induced family of copulas includes well-known copula classes, such as the BB1, BB2, and BB4 copulas, as special cases. The unit-Burr distortion of existing bivariate copulas may result in a family of copulas with both lower and upper tail coefficients ranging from 0 to 1. An empirical application to the rates of return for Microsoft and Google stocks is presented. Full article
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23 pages, 1008 KiB  
Article
An Integrated Structural Equation Modelling and Machine Learning Framework for Measurement Scale Evaluation—Application to Voluntary Turnover Intentions
by Marcin Nowak and Robert Zajkowski
AppliedMath 2025, 5(3), 105; https://doi.org/10.3390/appliedmath5030105 - 13 Aug 2025
Viewed by 207
Abstract
There is an increasing demand for robust methodologies to rigorously evaluate the psychometric properties of measurement scales used in quantitative research across various scientific disciplines. This article proposes an integrative method that combines structural equation modelling (SEM) with machine learning (ML) to jointly [...] Read more.
There is an increasing demand for robust methodologies to rigorously evaluate the psychometric properties of measurement scales used in quantitative research across various scientific disciplines. This article proposes an integrative method that combines structural equation modelling (SEM) with machine learning (ML) to jointly assess model fit and predictive accuracy, limitations often addressed separately in traditional approaches. Using a measurement scale for voluntary employee turnover intention, the method demonstrates clear improvements: RMSEA decreased from 0.073 to 0.065, and classifier accuracy slightly increased from 0.862 to 0.863 after removing three redundant items. Compared to standalone SEM or ML, the integrated framework yields a shorter, better-fitting scale without compromising predictive power. For practitioners, this method enables the creation of more efficient, theoretically grounded, and predictive tools, facilitating faster and more accurate assessments in organisational settings. To this end, this study employs Covariance-Based SEM (CB-SEM) in conjunction with classifiers such as naive Bayes, linear and nonlinear support vector machines, decision trees, k-nearest neighbours, and logistic regression. Full article
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19 pages, 1521 KiB  
Article
A Novel Approach for Modeling Strain Hardening in Plasticity and Its Material Parameter Identification by Bayesian Optimization for Automotive Structural Steels Application
by Teng Long, Leyu Wang, Cing-Dao Kan and James D. Lee
AppliedMath 2025, 5(3), 104; https://doi.org/10.3390/appliedmath5030104 - 12 Aug 2025
Viewed by 215
Abstract
Constitutive modeling in plasticity is a critical topic in solid mechanics. However, modeling nonlinear plasticity remains a challenge due to the theoretical complexity in representing realistic material behavior. This work aims to develop a general material model based on a rational polynomial function [...] Read more.
Constitutive modeling in plasticity is a critical topic in solid mechanics. However, modeling nonlinear plasticity remains a challenge due to the theoretical complexity in representing realistic material behavior. This work aims to develop a general material model based on a rational polynomial function for plasticity and to use Bayesian optimization to identify its parameters. As a data-driven approach, Bayesian optimization effectively estimates model parameters for a high-computational-cost model. In this work, automotive structural steel is selected as a representative example to benchmark the proposed approach. Our results demonstrate that the rational polynomial function effectively models the plasticity behavior for metallic alloy before the failure point, and Bayesian optimization successfully estimates the parameters. This novel framework also has the potential to be applied to other materials, whose constitutive models can be defined by stress–strain curves. Full article
(This article belongs to the Special Issue Optimization and Machine Learning)
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25 pages, 5030 KiB  
Article
Genetic Algorithm Optimization of Sales Routes with Time and Workload Objectives
by Filipa Costa, Margarida Brito, Pedro Louro and Sílvio Gama
AppliedMath 2025, 5(3), 103; https://doi.org/10.3390/appliedmath5030103 - 11 Aug 2025
Viewed by 291
Abstract
This work proposes a novel multi-objective genetic algorithm to solve the Periodic Vehicle Routing Problem with Time Windows (PVRPTWs) tailored for sales teams with diverse geographic scales and visit frequency requirements. Unlike existing models, our approach incorporates workload balancing and applies a clustering-based [...] Read more.
This work proposes a novel multi-objective genetic algorithm to solve the Periodic Vehicle Routing Problem with Time Windows (PVRPTWs) tailored for sales teams with diverse geographic scales and visit frequency requirements. Unlike existing models, our approach incorporates workload balancing and applies a clustering-based preprocessing step for long-distance routes using multidimensional scaling and fuzzy clustering, improving initial route grouping. When tested on three salesperson profiles (short-, mid-, and long-distance), the model achieved up to a 69% reduction in total travel time compared to a nearest neighbor baseline. These results demonstrate substantial improvements over existing methods and underscore the model’s flexibility and potential for extension to dynamic or real-time sales routing applications. Full article
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12 pages, 688 KiB  
Article
A New Index for Measuring the Non-Uniformity of a Probability Distribution
by Hening Huang
AppliedMath 2025, 5(3), 102; https://doi.org/10.3390/appliedmath5030102 - 8 Aug 2025
Viewed by 181
Abstract
This paper proposes a new index, the “distribution non-uniformity index (DNUI)”, for quantitatively measuring the non-uniformity or unevenness of a probability distribution relative to a baseline uniform distribution. The proposed DNUI is a normalized, distance-based metric ranging between 0 and 1, with 0 [...] Read more.
This paper proposes a new index, the “distribution non-uniformity index (DNUI)”, for quantitatively measuring the non-uniformity or unevenness of a probability distribution relative to a baseline uniform distribution. The proposed DNUI is a normalized, distance-based metric ranging between 0 and 1, with 0 indicating perfect uniformity and 1 indicating extreme non-uniformity. It satisfies our axioms for an effective non-uniformity index and is applicable to both discrete and continuous probability distributions. Several examples are presented to demonstrate its application and to compare it with two distance measures, namely, the Hellinger distance (HD) and the total variation distance (TVD), and two classical evenness measures, namely, Simpson’s evenness and Buzas and Gibson’s evenness. Full article
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25 pages, 6742 KiB  
Article
Reservoir Computing with a Single Oscillating Gas Bubble: Emphasizing the Chaotic Regime
by Hend Abdel-Ghani, A. H. Abbas and Ivan S. Maksymov
AppliedMath 2025, 5(3), 101; https://doi.org/10.3390/appliedmath5030101 - 7 Aug 2025
Viewed by 209
Abstract
The rising computational and energy demands of artificial intelligence systems urge the exploration of alternative software and hardware solutions that exploit physical effects for computation. According to machine learning theory, a neural network-based computational system must exhibit nonlinearity to effectively model complex patterns [...] Read more.
The rising computational and energy demands of artificial intelligence systems urge the exploration of alternative software and hardware solutions that exploit physical effects for computation. According to machine learning theory, a neural network-based computational system must exhibit nonlinearity to effectively model complex patterns and relationships. This requirement has driven extensive research into various nonlinear physical systems to enhance the performance of neural networks. In this paper, we propose and theoretically validate a reservoir-computing system based on a single bubble trapped within a bulk of liquid. By applying an external acoustic pressure wave to both encode input information and excite the complex nonlinear dynamics, we showcase the ability of this single-bubble reservoir-computing system to forecast a Hénon benchmarking time series and undertake classification tasks with high accuracy. Specifically, we demonstrate that a chaotic physical regime of bubble oscillation—where tiny differences in initial conditions lead to wildly different outcomes, making the system unpredictable despite following clear rules, yet still suitable for accurate computations—proves to be the most effective for such tasks. Full article
(This article belongs to the Topic A Real-World Application of Chaos Theory)
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33 pages, 1043 KiB  
Article
Uncovering the Psychometric Properties of Statistics Anxiety in Graduate Courses at a Minority-Serving Institution: Insights from Exploratory and Bayesian Structural Equation Modeling in a Small Sample Context
by Hyeri Hong, Ryan E. Ditchfield and Christian Wandeler
AppliedMath 2025, 5(3), 100; https://doi.org/10.3390/appliedmath5030100 - 6 Aug 2025
Viewed by 240
Abstract
The Statistics Anxiety Rating Scale (STARS) is a 51-item scale commonly used to measure college students’ anxiety regarding statistics. To date, however, limited empirical research exists that examines statistics anxiety among ethnically diverse or first-generation graduate students. We examined the factor structure and [...] Read more.
The Statistics Anxiety Rating Scale (STARS) is a 51-item scale commonly used to measure college students’ anxiety regarding statistics. To date, however, limited empirical research exists that examines statistics anxiety among ethnically diverse or first-generation graduate students. We examined the factor structure and reliability of STARS scores in a diverse sample of students enrolled in graduate courses at a Minority-Serving Institution (n = 194). To provide guidance on assessing dimensionality in small college samples, we compared the performance of best-practice factor analysis techniques: confirmatory factor analysis (CFA), exploratory structural equation modeling (ESEM), and Bayesian structural equation modeling (BSEM). We found modest support for the original six-factor structure using CFA, but ESEM and BSEM analyses suggested that a four-factor model best captures the dimensions of the STARS instrument within the context of graduate-level statistics courses. To enhance scale efficiency and reduce respondent fatigue, we also tested and found support for a reduced 25-item version of the four-factor STARS scale. The four-factor STARS scale produced constructs representing task and process anxiety, social support avoidance, perceived lack of utility, and mathematical self-efficacy. These findings extend the validity and reliability evidence of the STARS inventory to include diverse graduate student populations. Accordingly, our findings contribute to the advancement of data science education and provide recommendations for measuring statistics anxiety at the graduate level and for assessing construct validity of psychometric instruments in small or hard-to-survey populations. Full article
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30 pages, 825 KiB  
Review
Predictive Analytics in Human Resources Management: Evaluating AIHR’s Role in Talent Retention
by Ana Maria Căvescu and Nirvana Popescu
AppliedMath 2025, 5(3), 99; https://doi.org/10.3390/appliedmath5030099 - 5 Aug 2025
Viewed by 925
Abstract
This study explores the role of artificial intelligence (AI) in human resource management (HRM), with a focus on recruitment, employee retention, and performance optimization. Through a PRISMA-based systematic literature review, the paper examines many machine learning algorithms including XGBoost, SVM, random forest, and [...] Read more.
This study explores the role of artificial intelligence (AI) in human resource management (HRM), with a focus on recruitment, employee retention, and performance optimization. Through a PRISMA-based systematic literature review, the paper examines many machine learning algorithms including XGBoost, SVM, random forest, and linear regression in decision-making related to employee-attrition prediction and talent management. The findings suggest that these technologies can automate HR processes, reduce bias, and personalize employee experiences. However, the implementation of AI in HRM also presents challenges, including data privacy concerns, algorithmic bias, and organizational resistance. To address these obstacles, the study highlights the importance of adopting ethical AI frameworks, ensuring transparency in decision-making, and developing effective integration strategies. Future research should focus on improving explainability, minimizing algorithmic bias, and promoting fairness in AI-driven HR practices. Full article
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25 pages, 3362 KiB  
Article
The Double Laplace–Adomian Method for Solving Certain Nonlinear Problems in Applied Mathematics
by Oswaldo González-Gaxiola
AppliedMath 2025, 5(3), 98; https://doi.org/10.3390/appliedmath5030098 - 1 Aug 2025
Viewed by 218
Abstract
The objective of this investigation is to obtain numerical solutions for a variety of mathematical models in a wide range of disciplines, such as chemical kinetics, neurosciences, nonlinear optics, metallurgical separation/alloying processes, and asset dynamics in mathematical finance. This research features numerical simulations [...] Read more.
The objective of this investigation is to obtain numerical solutions for a variety of mathematical models in a wide range of disciplines, such as chemical kinetics, neurosciences, nonlinear optics, metallurgical separation/alloying processes, and asset dynamics in mathematical finance. This research features numerical simulations conducted with a remarkably low error measure, providing a visual representation of the examined models in these areas. The proposed method is the double Laplace–Adomian decomposition method, which facilitates the numerical acquisition and analysis of solutions. This paper presents the first report of numerical simulations employing this innovative methodology to address these problems. The findings are expected to benefit the natural sciences, mathematical modeling, and their practical applications, representing the innovative aspect of this article. Additionally, this method can analyze many classes of partial differential equations, whether linear or nonlinear, without the need for linearization or discretization. Full article
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28 pages, 437 KiB  
Article
The General Semimartingale Market Model
by Moritz Sohns
AppliedMath 2025, 5(3), 97; https://doi.org/10.3390/appliedmath5030097 - 1 Aug 2025
Viewed by 370
Abstract
This paper develops a unified framework for mathematical finance under general semimartingale models that allow for dividend payments, negative asset prices, and unbounded jumps. We present a rigorous approach to the mathematical modeling of financial markets with dividend-paying assets by defining appropriate concepts [...] Read more.
This paper develops a unified framework for mathematical finance under general semimartingale models that allow for dividend payments, negative asset prices, and unbounded jumps. We present a rigorous approach to the mathematical modeling of financial markets with dividend-paying assets by defining appropriate concepts of numéraires, discounted processes, and self-financing trading strategies. While most of the mathematical results are not new, this unified framework has been missing in the literature. We carefully examine the transition between nominal and discounted price processes and define appropriate notions of admissible strategies that work naturally in both settings. By establishing the equivalence between these models and providing clear conditions for their applicability, we create a mathematical foundation that encompasses a wide range of realistic market scenarios and can serve as a basis for future work on mathematical finance and derivative pricing. We demonstrate the practical relevance of our framework through a comprehensive application to dividend-paying equity markets where the framework naturally handles discrete dividend payments. This application shows that our theoretical framework is not merely abstract but provides the rigorous foundation for pricing derivatives in real-world markets where classical assumptions need extension. Full article
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17 pages, 438 KiB  
Article
Analytic Solutions and Conservation Laws of a 2D Generalized Fifth-Order KdV Equation with Power Law Nonlinearity Describing Motions in Shallow Water Under a Gravity Field of Long Waves
by Chaudry Masood Khalique and Boikanyo Pretty Sebogodi
AppliedMath 2025, 5(3), 96; https://doi.org/10.3390/appliedmath5030096 - 31 Jul 2025
Viewed by 178
Abstract
The Korteweg–de Vries (KdV) equation is a nonlinear evolution equation that reflects a wide variety of dispersive wave occurrences with limited amplitude. It has also been used to describe a range of major physical phenomena, such as shallow water waves that interact weakly [...] Read more.
The Korteweg–de Vries (KdV) equation is a nonlinear evolution equation that reflects a wide variety of dispersive wave occurrences with limited amplitude. It has also been used to describe a range of major physical phenomena, such as shallow water waves that interact weakly and nonlinearly, acoustic waves on a crystal lattice, lengthy internal waves in density-graded oceans, and ion acoustic waves in plasma. The KdV equation is one of the most well-known soliton models, and it provides a good platform for further research into other equations. The KdV equation has several forms. The aim of this study is to introduce and investigate a (2+1)-dimensional generalized fifth-order KdV equation with power law nonlinearity (gFKdVp). The research methodology employed is the Lie group analysis. Using the point symmetries of the gFKdVp equation, we transform this equation into several nonlinear ordinary differential equations (ODEs), which we solve by employing different strategies that include Kudryashov’s method, the (G/G) expansion method, and the power series expansion method. To demonstrate the physical behavior of the equation, 3D, density, and 2D graphs of the obtained solutions are presented. Finally, utilizing the multiplier technique and Ibragimov’s method, we derive conserved vectors of the gFKdVp equation. These include the conservation of energy and momentum. Thus, the major conclusion of the study is that analytic solutions and conservation laws of the gFKdVp equation are determined. Full article
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17 pages, 776 KiB  
Article
A Well-Conditioned Spectral Galerkin–Levin Method for Highly Oscillatory Integrals
by Viktoriya Pasternak, Heorhiy Sulym, Andrii Korniichuk and Iaroslav Pasternak
AppliedMath 2025, 5(3), 95; https://doi.org/10.3390/appliedmath5030095 - 25 Jul 2025
Viewed by 257
Abstract
This paper addresses the numerical evaluation of highly oscillatory integrals by developing a spectral Galerkin–Levin approach that efficiently solves Levin’s differential equation formulation for such integrals. The method employs Legendre polynomials as basis functions to approximate the solution, leveraging their orthogonality and favorable [...] Read more.
This paper addresses the numerical evaluation of highly oscillatory integrals by developing a spectral Galerkin–Levin approach that efficiently solves Levin’s differential equation formulation for such integrals. The method employs Legendre polynomials as basis functions to approximate the solution, leveraging their orthogonality and favorable numerical properties. A key finding is that the Galerkin–Levin formulation is invariant with respect to the choice of polynomial basis—be it monomials or classical orthogonal polynomials—although the use of Legendre polynomials leads to a more straightforward derivation of practical quadrature rules. Building on this, this paper derives a simple and efficient numerical quadrature for both scalar and matrix-valued highly oscillatory integrals. The proposed approach is computationally stable and well-conditioned, overcoming the limitations of collocation-based methods. Several numerical examples validate the method’s high accuracy, stability, and computational efficiency. Full article
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14 pages, 691 KiB  
Article
Availability of Hydropressor Systems: Redundancy and Multiple Failure Modes
by Ricardo Enguiça and Sérgio Lopes
AppliedMath 2025, 5(3), 94; https://doi.org/10.3390/appliedmath5030094 - 18 Jul 2025
Viewed by 274
Abstract
Hydropressor systems are of paramount importance in keeping water supplies running properly. A typical such device consists of two (or more) identical electropumps operating alternately, so as to avoid downtime as much as possible. We consider a dual pump configuration to identify the [...] Read more.
Hydropressor systems are of paramount importance in keeping water supplies running properly. A typical such device consists of two (or more) identical electropumps operating alternately, so as to avoid downtime as much as possible. We consider a dual pump configuration to identify the ideal usage proportion of each pump (from 0%-100%, meaning interchange only upon failure, to 50%-50%, where each pump works half the time) in order to improve availability, accounting solely for corrective maintenance. We also address the possibility of improving the availability of a single pump under the hazard of failure in three different ways (with their own occurrence frequencies), while also accounting for preventive maintenance. Both settings are tackled through Monte Carlo simulation and the models are implemented with the Python 3.12 programming language. The results indicate that significant improvements to standard industry practices can be made. Full article
(This article belongs to the Special Issue Advances in Intelligent Control for Solving Optimization Problems)
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14 pages, 1614 KiB  
Article
Neural Networks and Markov Categories
by Sebastian Pardo-Guerra, Johnny Jingze Li, Kalyan Basu and Gabriel A. Silva
AppliedMath 2025, 5(3), 93; https://doi.org/10.3390/appliedmath5030093 - 18 Jul 2025
Viewed by 447
Abstract
We present a formal framework for modeling neural network dynamics using Category Theory, specifically through Markov categories. In this setting, neural states are represented as objects and state transitions as Markov kernels, i.e., morphisms in the category. This categorical perspective offers an algebraic [...] Read more.
We present a formal framework for modeling neural network dynamics using Category Theory, specifically through Markov categories. In this setting, neural states are represented as objects and state transitions as Markov kernels, i.e., morphisms in the category. This categorical perspective offers an algebraic alternative to traditional approaches based on stochastic differential equations, enabling a rigorous and structured approach to studying neural dynamics as a stochastic process with topological insights. By abstracting neural states as submeasurable spaces and transitions as kernels, our framework bridges biological complexity with formal mathematical structure, providing a foundation for analyzing emergent behavior. As part of this approach, we incorporate concepts from Interacting Particle Systems and employ mean-field approximations to construct Markov kernels, which are then used to simulate neural dynamics via the Ising model. Our simulations reveal a shift from unimodal to multimodal transition distributions near critical temperatures, reinforcing the connection between emergent behavior and abrupt changes in system dynamics. Full article
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20 pages, 1104 KiB  
Article
A Novel Algorithm Based on the Bundle Method for Solving the Max-Cut Problem
by Fadhl Jawad Kadhim and Ahmed Sabah Al-Jilawi
AppliedMath 2025, 5(3), 92; https://doi.org/10.3390/appliedmath5030092 - 17 Jul 2025
Viewed by 296
Abstract
A novel algorithm was proposed for solving the max-cut problem, which seeks to identify the cut with the maximum weight in a given graph. Our technique is based on the bundle approach, applied to a newly formulated semidefinite relaxation. This research establishes the [...] Read more.
A novel algorithm was proposed for solving the max-cut problem, which seeks to identify the cut with the maximum weight in a given graph. Our technique is based on the bundle approach, applied to a newly formulated semidefinite relaxation. This research establishes the theoretical convergence of our approximation technique and presents the numerical results obtained on several large-scale graphs from the BiqMac library, specifically with 100, 250, and 500 nodes. The resulting performance was compared with that produced by two alternative semidefinite programming-based approximation methods, namely the BiqMac and BiqBin solvers, by comparing the CPU time and the number of function calls. The primary objective of this work was to enhance the scalability and computational efficiency in solving the max-cut problem, particularly for large-scale graph instances. Despite the development of numerous approximation algorithms, a persistent challenge lies in effectively handling problems with a large number of constraints. Our algorithm addresses this by integrating a novel semidefinite relaxation with a bundle-based optimization framework, achieving faster convergence and fewer function calls. These advancements mark a meaningful step forward in the efficient resolution of NP-hard combinatorial optimization problems. Full article
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17 pages, 10396 KiB  
Article
Feature Selection Based on Three-Dimensional Correlation Graphs
by Adam Dudáš and Aneta Szoliková
AppliedMath 2025, 5(3), 91; https://doi.org/10.3390/appliedmath5030091 - 17 Jul 2025
Viewed by 308
Abstract
The process of feature selection is a critical component of any decision-making system incorporating machine or deep learning models applied to multidimensional data. Feature selection on input data can be performed using a variety of techniques, such as correlation-based methods, wrapper-based methods, or [...] Read more.
The process of feature selection is a critical component of any decision-making system incorporating machine or deep learning models applied to multidimensional data. Feature selection on input data can be performed using a variety of techniques, such as correlation-based methods, wrapper-based methods, or embedded methods. However, many conventionally used approaches do not support backwards interpretability of the selected features, making their application in real-world scenarios impractical and difficult to implement. This work addresses that limitation by proposing a novel correlation-based strategy for feature selection in regression tasks, based on a three-dimensional visualization of correlation analysis results—referred to as three-dimensional correlation graphs. The main objective of this study is the design, implementation, and experimental evaluation of this graphical model through a case study using a multidimensional dataset with 28 attributes. The experiments assess the clarity of the visualizations and their impact on regression model performance, demonstrating that the approach reduces dimensionality while maintaining or improving predictive accuracy, enhances interpretability by uncovering hidden relationships, and achieves better or comparable results to conventional feature selection methods. Full article
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30 pages, 1477 KiB  
Article
Algebraic Combinatorics in Financial Data Analysis: Modeling Sovereign Credit Ratings for Greece and the Athens Stock Exchange General Index
by Georgios Angelidis and Vasilios Margaris
AppliedMath 2025, 5(3), 90; https://doi.org/10.3390/appliedmath5030090 - 15 Jul 2025
Viewed by 279
Abstract
This study investigates the relationship between sovereign credit rating transitions and domestic equity market performance, focusing on Greece from 2004 to 2024. Although credit ratings are central to sovereign risk assessment, their immediate influence on financial markets remains contested. This research adopts a [...] Read more.
This study investigates the relationship between sovereign credit rating transitions and domestic equity market performance, focusing on Greece from 2004 to 2024. Although credit ratings are central to sovereign risk assessment, their immediate influence on financial markets remains contested. This research adopts a multi-method analytical framework combining algebraic combinatorics and time-series econometrics. The methodology incorporates the construction of a directed credit rating transition graph, the partially ordered set representation of rating hierarchies, rolling-window correlation analysis, Granger causality testing, event study evaluation, and the formulation of a reward matrix with optimal rating path optimization. Empirical results indicate that credit rating announcements in Greece exert only modest short-term effects on the Athens Stock Exchange General Index, implying that markets often anticipate these changes. In contrast, sequential downgrade trajectories elicit more pronounced and persistent market responses. The reward matrix and path optimization approach reveal structured investor behavior that is sensitive to the cumulative pattern of rating changes. These findings offer a more nuanced interpretation of how sovereign credit risk is processed and priced in transparent and fiscally disciplined environments. By bridging network-based algebraic structures and economic data science, the study contributes a novel methodology for understanding systemic financial signals within sovereign credit systems. Full article
(This article belongs to the Special Issue Algebraic Combinatorics in Data Science and Optimisation)
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11 pages, 1733 KiB  
Article
PV Panels Fault Detection Video Method Based on Mini-Patterns
by Codrin Donciu, Marinel Costel Temneanu and Elena Serea
AppliedMath 2025, 5(3), 89; https://doi.org/10.3390/appliedmath5030089 - 10 Jul 2025
Viewed by 297
Abstract
The development of solar technologies and the widespread adoption of photovoltaic (PV) panels have significantly transformed the global energy landscape. PV panels have evolved from niche applications to become a primary source of electricity generation, driven by their environmental benefits and declining costs. [...] Read more.
The development of solar technologies and the widespread adoption of photovoltaic (PV) panels have significantly transformed the global energy landscape. PV panels have evolved from niche applications to become a primary source of electricity generation, driven by their environmental benefits and declining costs. However, the performance and operational lifespan of PV systems are often compromised by various faults, which can lead to efficiency losses and increased maintenance costs. Consequently, effective and timely fault detection methods have become a critical focus of current research in the field. This work proposes an innovative video-based method for the dimensional evaluation and detection of malfunctions in solar panels, utilizing processing techniques applied to aerial images captured by unmanned aerial vehicles (drones). The method is based on a novel mini-pattern matching algorithm designed to identify specific defect features despite challenging environmental conditions such as strong gradients of non-uniform lighting, partial shading effects, or the presence of accidental deposits that obscure panel surfaces. The proposed approach aims to enhance the accuracy and reliability of fault detection, enabling more efficient monitoring and maintenance of PV installations. Full article
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16 pages, 1682 KiB  
Article
ACS2-Powered Pedestrian Flow Simulation for Crowd Dynamics
by Tomohiro Hayashida, Shinya Sekizaki, Yushi Furuya and Ichiro Nishizaki
AppliedMath 2025, 5(3), 88; https://doi.org/10.3390/appliedmath5030088 - 9 Jul 2025
Viewed by 318
Abstract
Pedestrian flow simulations play a pivotal role in urban planning, transportation engineering, and disaster response by enabling the detailed analysis of crowd dynamics and walking behavior. While physical models such as the Social Force model and Boids have been widely used, they often [...] Read more.
Pedestrian flow simulations play a pivotal role in urban planning, transportation engineering, and disaster response by enabling the detailed analysis of crowd dynamics and walking behavior. While physical models such as the Social Force model and Boids have been widely used, they often struggle to replicate complex inter-agent interactions. On the other hand, reinforcement learning (RL) methods, although adaptive, suffer from limited interpretability due to their opaque policy structures. To address these limitations, this study proposes a pedestrian simulation framework based on the Anticipatory Classifier System 2 (ACS2), a rule-based evolutionary learning model capable of extracting explicit behavior rules through trial-and-error learning. The proposed model captures the interactions between agents and environmental features while preserving the interpretability of the acquired strategies. Simulation experiments demonstrate that the ACS2-based agents reproduce realistic pedestrian dynamics and achieve comparable adaptability to conventional reinforcement learning approaches such as tabular Q-learning. Moreover, the extracted behavior rules enable systematic analysis of movement patterns, including the effects of obstacles and crowd composition on flow efficiency and group alignment. The results suggest that the ACS2 provides a promising approach to constructing interpretable multi-agent simulations for real-world pedestrian environments. Full article
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20 pages, 317 KiB  
Article
Linking Controllability to the Sturm–Liouville Problem in Ordinary Time-Varying Second-Order Differential Equations
by Manuel De la Sen
AppliedMath 2025, 5(3), 87; https://doi.org/10.3390/appliedmath5030087 - 8 Jul 2025
Viewed by 297
Abstract
This paper establishes some links between Sturm–Liouville problems and the well-known controllability property in linear dynamic systems, together with a control law design that allows any prefixed arbitrary final state finite value to be reached via feedback from any given finite initial conditions. [...] Read more.
This paper establishes some links between Sturm–Liouville problems and the well-known controllability property in linear dynamic systems, together with a control law design that allows any prefixed arbitrary final state finite value to be reached via feedback from any given finite initial conditions. The scheduled second-order dynamic systems are equivalent to the stated second-order differential equations, and they are used for analysis purposes. In the first study, a control law is synthesized for a forced time-invariant nominal version of the current time-varying one so that their respective two-point boundary values are coincident. Afterward, the parameter that fixes the set of eigenvalues of the Sturm–Liouville system is replaced by a time-varying parameter that is a control function to be synthesized without performing, in this case, any comparison with a nominal time-invariant version of the system. Such a control law is designed in such a way that, for given arbitrary and finite initial conditions of the differential system, prescribed final conditions along a time interval of finite length are matched by the state trajectory solution. As a result, the solution of the dynamic system, and thus that of its differential equation counterpart, is subject to prefixed two-point boundary values at the initial and at the final time instants of the time interval of finite length under study. Also, some algebraic constraints between the eigenvalues of the Sturm–Liouville system and their evolution operators are formulated later on. Those constraints are based on the fact that the solutions corresponding to each of the eigenvalues match the same two-point boundary values. Full article
17 pages, 498 KiB  
Article
Assessing Standard Error Estimation Approaches for Robust Mean-Geometric Mean Linking
by Alexander Robitzsch
AppliedMath 2025, 5(3), 86; https://doi.org/10.3390/appliedmath5030086 - 4 Jul 2025
Viewed by 267
Abstract
Robust mean-geometric mean (MGM) linking methods enable reliable group comparisons in item response theory models under fixed and sparse differential item functioning. This article evaluates six alternative standard error and confidence interval (CI) estimation methods across four MGM linking approaches. Our Simulation Study [...] Read more.
Robust mean-geometric mean (MGM) linking methods enable reliable group comparisons in item response theory models under fixed and sparse differential item functioning. This article evaluates six alternative standard error and confidence interval (CI) estimation methods across four MGM linking approaches. Our Simulation Study demonstrates that CIs based on the delta method or bootstrap procedures using the normal distribution or empirical quantiles exhibit highly inflated coverage rates. In contrast, CIs derived from a weighted least squares estimation problem, as well as basic and bias-corrected bootstrap methods, yield satisfactory coverage rates in most simulation conditions for robust MGM linking. Full article
12 pages, 19663 KiB  
Article
Growth of a Long Bone Section Based on Inorganic Hydroxyapatite Crystals as Cellular Automata
by César Renán Acosta, Irma Martín and Gabriela Rivadeneyra
AppliedMath 2025, 5(3), 85; https://doi.org/10.3390/appliedmath5030085 - 4 Jul 2025
Viewed by 234
Abstract
This work explores the morphogenesis of the skeletal mineral component, with a specific emphasis on hydroxyapatite (HAp) crystal assembly. Bone is fundamentally a triphasic biomaterial, consisting of an inorganic mineral phase, an organic matrix, and an aqueous component. The inorganic phase (hydroxyapatite), is [...] Read more.
This work explores the morphogenesis of the skeletal mineral component, with a specific emphasis on hydroxyapatite (HAp) crystal assembly. Bone is fundamentally a triphasic biomaterial, consisting of an inorganic mineral phase, an organic matrix, and an aqueous component. The inorganic phase (hydroxyapatite), is characterized by its hexagonal prismatic nanocrystalline structure. We leverage a cellular automata (CA) paradigm to computationally simulate the mineralization process, leading to the formation of the bone’s hydroxyapatite framework. This model exclusively considers the physicochemical aspects of bone formation, intentionally excluding the biological interactions that govern in vivo skeletal development. To optimize computational efficiency, a simplified anatomical segment of a long bone (e.g., the femur) is modeled. This geometric simplification encompasses an outer ellipsoidal cylindrical boundary (periosteal envelope), an inner ellipsoidal surface defining the interface between cortical and cancellous bone, and a central circular cylindrical lumen representing the medullary cavity, which accommodates the bone marrow and primary vasculature. The CA methodology is applied to generate the internal bone microarchitecture, while deliberately omitting the design of smaller, secondary vascular channels. Full article
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18 pages, 1070 KiB  
Article
Assessing the Quality of Virtual Student Internships in Brazilian Organizations: Potential and Use of Fuzzy TOPSIS Class
by Vitório Henrique Agostini Marinato, Gustavo Tietz Cazeri, Gustavo Hermínio Salati Marcondes de Moraes, Lucas Gabriel Zanon, Tiago F. A. C. Sigahi, Izabela Simon Rampasso and Rosley Anholon
AppliedMath 2025, 5(3), 84; https://doi.org/10.3390/appliedmath5030084 - 2 Jul 2025
Viewed by 307
Abstract
This research delves into the assessment of students’ perspectives regarding virtual internships within Brazilian organizations, a phenomenon accelerated by the global pandemic. Evaluating 78 students’ virtual internships via a survey, the study employs the Fuzzy TOPSIS Class method for analysis. Additionally, a sensitivity [...] Read more.
This research delves into the assessment of students’ perspectives regarding virtual internships within Brazilian organizations, a phenomenon accelerated by the global pandemic. Evaluating 78 students’ virtual internships via a survey, the study employs the Fuzzy TOPSIS Class method for analysis. Additionally, a sensitivity analysis was conducted to assess the robustness of the results. Key insights for enhancing virtual internships encompass: emphasizing application and deeper understanding of topics learned during the undergraduate course, enhancing understanding about how organizations work, and fostering comprehension of market dynamics. Among the points best rated by students are the opportunity to explore new subjects, development of soft skills, and supervisors’ competence in managing teams in virtual environments. This paper contributes methodologically by proposing a multicriteria decision-making approach to assess virtual internships. The findings serve as a valuable resource for internship supervisors in companies and higher education institutions, aiding them in guiding students through this pivotal developmental phase that shapes their future careers. Full article
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16 pages, 335 KiB  
Article
Locally RSD-Generated Parametrized G1-Spline Surfaces Interpolating First-Order Data over 3D Triangular Meshes
by László L. Stachó
AppliedMath 2025, 5(3), 83; https://doi.org/10.3390/appliedmath5030083 - 2 Jul 2025
Viewed by 237
Abstract
Given a triangular mesh in R3 with a family of points associated with its vertices along with vectors associated with its edges, we propose a novel technique for the construction of locally generated fitting parametrized G1-spline interpolation surfaces. The method consists of [...] Read more.
Given a triangular mesh in R3 with a family of points associated with its vertices along with vectors associated with its edges, we propose a novel technique for the construction of locally generated fitting parametrized G1-spline interpolation surfaces. The method consists of a G1 correction over the mesh edges of the mesh triangles, produced using reduced side derivatives (RSDs) introduced earlier by the author in terms of the barycentric weight functions. In the case of polynomial RSD shape functions, we establish polynomial edge corrections via an algorithm with an independent interest in determining the optimal GCD cofactors with the lowest degree for arbitrary families of polynomials. Full article
21 pages, 1998 KiB  
Article
Computational Modeling and Optimization of Deep Learning for Multi-Modal Glaucoma Diagnosis
by Vaibhav C. Gandhi, Priyesh Gandhi, John Omomoluwa Ogundiran, Maurice Samuntu Sakaji Tshibola and Jean-Paul Kapuya Bulaba Nyembwe
AppliedMath 2025, 5(3), 82; https://doi.org/10.3390/appliedmath5030082 - 2 Jul 2025
Viewed by 436
Abstract
Glaucoma is a leading cause of irreversible blindness globally, with early diagnosis being crucial to preventing vision loss. Traditional diagnostic methods, including fundus photography, OCT imaging, and perimetry, often fall short in sensitivity and fail to integrate structural and functional data. This study [...] Read more.
Glaucoma is a leading cause of irreversible blindness globally, with early diagnosis being crucial to preventing vision loss. Traditional diagnostic methods, including fundus photography, OCT imaging, and perimetry, often fall short in sensitivity and fail to integrate structural and functional data. This study proposes a novel multi-modal diagnostic framework that combines convolutional neural networks (CNNs), vision transformers (ViTs), and quantum-enhanced layers to improve glaucoma detection accuracy and efficiency. The framework integrates fundus images, OCT scans, and clinical biomarkers, leveraging their complementary strengths through a weighted fusion mechanism. Datasets, including the GRAPE and other public and clinical sources, were used, ensuring diverse demographic representation and supporting generalizability. The model was trained and validated using cross-entropy loss, L2 regularization, and adaptive learning strategies, achieving an accuracy of 96%, sensitivity of 94%, and an AUC of 0.97—outperforming CNN-only and ViT-only approaches. Additionally, the quantum-enhanced architecture reduced computational complexity from O(n2) to O (log n), enabling real-time deployment with a 40% reduction in FLOPs. The proposed system addresses key limitations of previous methods in terms of computational cost, data integration, and interpretability. The proposed system addresses key limitations of previous methods in terms of computational cost, data integration, and interpretability. This framework offers a scalable and clinically viable tool for early glaucoma detection, supporting personalized care and improving diagnostic workflows in ophthalmology. Full article
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16 pages, 3471 KiB  
Article
Unraveling Functional Segregation: Methods for Identifying Modules in Brain Networks
by Tahmineh Azizi
AppliedMath 2025, 5(3), 81; https://doi.org/10.3390/appliedmath5030081 - 1 Jul 2025
Viewed by 348
Abstract
Functional segregation in brain networks refers to the division of specialized cognitive functions across distinct regions, enabling efficient and dedicated information processing. This paper explores the significance of functional segregation in shaping brain network architecture, highlighting methodologies such as modularity and local efficiency [...] Read more.
Functional segregation in brain networks refers to the division of specialized cognitive functions across distinct regions, enabling efficient and dedicated information processing. This paper explores the significance of functional segregation in shaping brain network architecture, highlighting methodologies such as modularity and local efficiency that quantify the degree of specialization and intra-regional communication. We examine how these metrics reveal the presence of specialized modules underpinning various cognitive processes and behaviors and discuss the implications of disruptions in functional segregation in neurological and psychiatric disorders. Our findings underscore the fact that understanding functional segregation is crucial for elucidating normal brain function, identifying biomarkers, and developing therapeutic interventions. Overall, functional segregation is a fundamental principle governing brain organization, and ongoing research into its mechanisms promises to advance our comprehension of the brain’s complex architecture and its impact on human health. Full article
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17 pages, 2302 KiB  
Article
Temporal Evolution of Small-Amplitude Internal Gravity Waves Generated by Latent Heating in an Anelastic Fluid Flow
by Amir A. M. Sayed, Amna M. Grgar and Lucy J. Campbell
AppliedMath 2025, 5(3), 80; https://doi.org/10.3390/appliedmath5030080 - 30 Jun 2025
Viewed by 201
Abstract
A two-dimensional time-dependent model is presented for upward-propagating internal gravity waves generated by an imposed thermal forcing in a layer of fluid with uniform background velocity and stable stratification under the anelastic approximation. The configuration studied is representative of a situation with deep [...] Read more.
A two-dimensional time-dependent model is presented for upward-propagating internal gravity waves generated by an imposed thermal forcing in a layer of fluid with uniform background velocity and stable stratification under the anelastic approximation. The configuration studied is representative of a situation with deep or shallow latent heating in the lower atmosphere where the amplitude of the waves is small enough to allow linearization of the model equations. Approximate asymptotic time-dependent solutions, valid for late time, are obtained for the linearized equations in the form of an infinite series of terms involving Bessel functions. The asymptotic solution approaches a steady-amplitude state in the limit of infinite time. A weakly nonlinear analysis gives a description of the temporal evolution of the zonal mean flow velocity and temperature resulting from nonlinear interaction with the waves. The linear solutions show that there is a vertical variation of the wave amplitude which depends on the relative depth of the heating to the scale height of the atmosphere. This means that, from a weakly nonlinear perspective, there is a non-zero divergence of vertical momentum flux, and hence, a non-zero drag force, even in the absence of vertical shear in the background flow. Full article
(This article belongs to the Special Issue Exploring the Role of Differential Equations in Climate Modeling)
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29 pages, 4203 KiB  
Article
A Lightweight Deep Learning and Sorting-Based Smart Parking System for Real-Time Edge Deployment
by Muhammad Omair Khan, Muhammad Asif Raza, Md Ariful Islam Mozumder, Ibad Ullah Azam, Rashadul Islam Sumon and Hee Cheol Kim
AppliedMath 2025, 5(3), 79; https://doi.org/10.3390/appliedmath5030079 - 28 Jun 2025
Viewed by 627
Abstract
As cities grow denser, the demand for efficient parking systems becomes more critical to reduce traffic congestion, fuel consumption, and environmental impact. This paper proposes a smart parking solution that combines deep learning and algorithmic sorting to identify the nearest available parking slot [...] Read more.
As cities grow denser, the demand for efficient parking systems becomes more critical to reduce traffic congestion, fuel consumption, and environmental impact. This paper proposes a smart parking solution that combines deep learning and algorithmic sorting to identify the nearest available parking slot in real time. The system uses several pre-trained convolutional neural network (CNN) models—VGG16, ResNet50, Xception, LeNet, AlexNet, and MobileNet—along with a lightweight custom CNN architecture, all trained on a custom parking dataset. These models are integrated into a mobile application that allows users to view and request nearby parking spaces. A merge sort algorithm ranks available slots based on proximity to the user. The system is validated using benchmark datasets (CNR-EXT and PKLot), demonstrating high accuracy across diverse weather conditions. The proposed system shows how applied mathematical models and deep learning can improve urban mobility through intelligent infrastructure. Full article
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