Selecciones Matemáticas https://revistas.unitru.edu.pe/index.php/SSMM <p>Journal of the Academic department of Mathematics of the <a href="http://www.unitru.edu.pe" target="_blank" rel="noopener">National University of Trujillo</a>. The purpose of the journal is to publish the results of original and unpublished research in the field of Mathematics and Applied Mathematics.</p> <p>"<strong>Selecciones Matemáticas</strong>" is an Open Access Journal.</p> <p><em><strong>ISSN-e: </strong></em><span class="apple-converted-space"> </span><strong>2411 - 1783</strong> <strong>DOI</strong>: <a href="https://revistas.unitru.edu.pe/index.php/SSMM" target="_blank" rel="noopener">10.17268/Sel.mat</a></p> <p><strong>Short title:</strong><span class="apple-converted-space"> </span>Sel.Mat. <img src="https://revistas.unitru.edu.pe/public/site/images/admrevffmm/Open_Acces1.png" alt="" /></p> <p><strong>----------------------------------------------------------------------------------------------------------------------------------------------------------</strong></p> <p> </p> National University of Trujillo - Academic Department of Mathematics en-US Selecciones Matemáticas 2411-1783 <p>The authors who publish in this journal accept the following conditions:<br />1. The authors retain the copyright and assign to the journal the right of the first publication, with the work registered with the <a href="https://creativecommons.org/licenses/by-nc-sa/4.0/">Creative Commons Attribution License</a>,<a title="Licencia" href="https://creativecommons.org/licenses/by/4.0/" target="_blank" rel="noopener">Atribución 4.0 Internacional <strong>(CC BY 4.0)</strong></a> which allows third parties to use what is published whenever they mention the authorship of the work And to the first publication in this magazine.<br />2. Authors may make other independent and additional contractual arrangements for non-exclusive distribution of the version of the article published in this journal (eg, include it in an institutional repository or publish it in a book) provided they clearly state that The paper was first published in this journal.<br />3. Authors are encouraged to publish their work on the Internet (for example, on institutional or personal pages) before and during the review and publication process, as it can lead to productive exchanges and to a greater and more rapid dissemination Of the published work.</p> Discrete Dynamic Systems in Economics: A Study of Linear Difference Equations and Nonlinear Models with Naive and Adaptive Expectations https://revistas.unitru.edu.pe/index.php/SSMM/article/view/6638 <p>This study investigates market dynamics using a discrete economic model of supply and demand.</p> <p>Initially, the linear case with naïve or static expectations is analyzed, and the stability conditions that lead to different system behaviors, such as convergence to equilibrium, periodic oscillations, or divergence, are determined analytically through the study of fixed points and cobweb dynamics.</p> <p>Subsequently, the analysis is extended to the nonlinear case with adaptive expectations, where the interaction between supply nonlinearity and the expectation formation process is found to generate complex behaviors. The results show how variations in the nonlinearity parameter induce bifurcations observable in time series. The study provides a comprehensive analytical framework that links mathematical properties with observable economic phenomena, offering tools to predict and manage stability in real markets, with direct applications in economic policy and financial risk management.</p> Jose Luis Matos Tejada Copyright (c) 2025 https://creativecommons.org/licenses/by/4.0 2025-07-26 2025-07-26 12 01 162 185 10.17268/sel.mat.2025.01.14 Fatou’s Theorem; its contribution to harmonic analysis https://revistas.unitru.edu.pe/index.php/SSMM/article/view/6639 <p>The objective of this article is to see how Fatou’s theorem, given at the beginning of the 20th century, motivated new developments in harmonic analysis and partial differential equations in the second half of that century. In this writing we give a brief tour of some of the contributions given by distinguished analysis and in this way our interest is to make such progress known in Peru and thus contribute to the development of this beautiful branch of mathematical analysis, which we believe is almost unknown in our country. In particular we have paid some attention to the work of Jerison - Kenig [1] because such work contains an overview that helps meet our objective.</p> Alejandro Ortiz Fernández Copyright (c) 2025 https://creativecommons.org/licenses/by/4.0 2025-07-26 2025-07-26 12 01 186 217 10.17268/sel.mat.2025.01.15 Applied mathematics, its importance in developing it in Peru https://revistas.unitru.edu.pe/index.php/SSMM/article/view/6640 <p>The objective of this article is to contribute with some ideas and proposals with the purpose of further developing the study and research in our country of this area of mathematics, given the historical background of how, thanks to it, many countries have achieved their technological development and in this way with the well-being of the respective society.</p> Alejandro Ortiz Fernández Copyright (c) 2025 https://creativecommons.org/licenses/by/4.0 2025-07-26 2025-07-26 12 01 218 242 10.17268/sel.mat.2025.01.16 On pullback attractors in non-autonomous dynamical systems https://revistas.unitru.edu.pe/index.php/SSMM/article/view/6641 <p>The theory of pullback attractors constitutes an important tool to interpret the dynamics of physical, biological or engineering phenomena, as it addresses the study of the asymptotic behavior of nonautonomous dynamic systems, where differential equations explicitly depend on time. The objective of this article seeks to synthesize recent advances, present some general techniques such as the energy estimations or asymptotic compactness. This work stick out the importance of pullback attractors to model systems with variable coefficients, memory, delays or in non-cylindrical domains and also points out some challenges such as extension to stochastic systems or complex geometries.</p> Carlos Felipe Vidarte Chavez Copyright (c) 2025 https://creativecommons.org/licenses/by/4.0 2025-07-26 2025-07-26 12 01 243 260 10.17268/sel.mat.2025.01.17 Integration of Monomials over the Unit Sphere and Unit Ball in Rn https://revistas.unitru.edu.pe/index.php/SSMM/article/view/6616 <p>We compute the integral of monomials of the form x^2β over the unit sphere and the unit&nbsp;ball in R^n where β = (β1, . . . , βn) is a multi–index with real components βk &gt; −1/2,&nbsp;1 ≤ k ≤ n, and discuss their asymptotic behavior as some, or all, βk → ∞. This allows&nbsp;for the evaluation of integrals involving circular and hyperbolic trigonometric functions&nbsp;over the unit sphere and the unit ball in Rn. We also consider the Fourier transform of&nbsp;monomials xα restricted to the unit sphere in Rn, where the multi–indices α have integer&nbsp;components, and discuss their behaviour at the origin.</p> Calixto P. Calderón Alberto Torchinsky Copyright (c) 2025 https://creativecommons.org/licenses/by/4.0 2025-07-26 2025-07-26 12 01 1 14 10.17268/sel.mat.2025.01.01 Euclidean space perturbed by a constant vector field and its relation to a Zermelo navigation problem https://revistas.unitru.edu.pe/index.php/SSMM/article/view/6642 <p>In this work, the authors perturb the Euclidean plane with a constant vector field of the form W = (0, ε) with 0 ≤ ε &lt; 1, which can be interpreted as wind currents affecting the movement of ships in a constant unidirectional way. It is observed that the resulting perturbed norm, called the ε-Euclidean metric, which is non-reversible, is a Finsler metric. In this way, a new non-Euclidean geometry is introduced. With this, the ε-Euclidean distance is induced and defined. This new way of measuring point-to-point distances can be interpreted, physically, as optimal travel time. Due to the non-reversibility of the ε-Euclidean metric, two types of circumferences are defined and characterized. Distance formulas (or optimal travel time) from point to line, from line to point, and from line to line are obtained, as well as a geometric construction technique for obtaining the distance from a point to a parabola, which can be adapted to other curves that simulate the Edge of a beach. Examples and graphs are presented for a better understanding of the work.</p> Dik D. Lujerio Garcia Newton M. Solórzano Chávez Marck A. Molina Morales Bibiano M. Cerna Maguiña Copyright (c) 2025 https://creativecommons.org/licenses/by/4.0 2025-07-26 2025-07-26 12 01 15 32 10.17268/sel.mat.2025.01.02 Surfaces with mean of the hyperbolic curvature radii of double harmonic type https://revistas.unitru.edu.pe/index.php/SSMM/article/view/6617 <p>In this paper, we define surfaces with mean of the hyperbolic curvature radii of double harmonic type (in short DHRMC-surfaces) in the hyperbolic space, these surfaces include the generalized Weingarten surfaces of the harmonic type (HGW-surfaces). We give a characterization of DHRMCsurfaces.</p> <p>Given a real function, we will present a family of DHRMC-surfaces that depend on two holomorphic functions. Moreover, we classify the DHRMC-surfaces of rotation.</p> Armando M. V. Corro Carlos M. C. Riveros Raquel P. de Aráujo Copyright (c) 2025 https://creativecommons.org/licenses/by/4.0 2025-07-26 2025-07-26 12 01 33 43 10.17268/sel.mat.2025.01.03 Traveling waves in a delayed reaction-diffusion SVIR epidemic model with generalized incidence function and imperfect vaccination https://revistas.unitru.edu.pe/index.php/SSMM/article/view/6618 <p>This paper is concerned with traveling wave solutions for a delayed reaction-diffusion SVIR epidemic model that includes both general incidence function and imperfect vaccination. In the model, the spread of infection in space is explicitly taken into account by using a heterogeneous environment; it takes into consideration the delay in immune response and inefficiency in vaccinations. The analysis carried out below shows that the basic reproduction number Ro will be a critical value for determining the existence of traveling waves. More precisely, when Ro &gt; 1 there exists a minimal wave speed ρ* &gt; 0 such that the system admits nontrivial traveling wave solutions for ρ ≥ ρ* whereas no such solutions exist for ρ &lt; ρ*. On the other hand, if Ro ≤ 1, there are no traveling wave solutions. The introduction of delays and imperfect vaccination adds richness and complexity to the dynamics, such as possible wave speed adjustments and pattern formations, which are hallmarks of complex systems. This work develops a theoretical framework that shall guide the understanding of how delays, spatial spread, and control measures interact in epidemic systems and offers insights applicable to real-world infectious disease dynamics. Numerical simulations for some typical nonlinear incidence functions are given in the last to illustrate the existence of traveling waves.</p> Rassim Darazirar Copyright (c) 2025 https://creativecommons.org/licenses/by/4.0 2025-07-26 2025-07-26 12 01 44 61 10.17268/sel.mat.2025.01.04 Some Variants of Wayment's Mean Value Theorem for Integrals https://revistas.unitru.edu.pe/index.php/SSMM/article/view/6619 <p>This note deals with some variants of Wayment’s Mean Value Theorem for integrals. Our approach is rather elementary and does not use advanced techniques from analysis. The simple auxiliary functions were used to prove the results.</p> German Lozada-Cruz Copyright (c) 2025 https://creativecommons.org/licenses/by/4.0 2025-07-26 2025-07-26 12 01 62 66 10.17268/sel.mat.2025.01.05 A mathematical analysis of an eco-epidemiological model with prey-feedback effect and prey-refuge https://revistas.unitru.edu.pe/index.php/SSMM/article/view/6621 <p>This study investigates an eco-epidemiological model incorporating feedback mechanisms and prey refuge, formulated as a system of nonlinear ordinary differential equations. The model describes interactions among susceptible prey, infected prey, and predators, including disease transmisión and nonlinear predation effects. We establish the existence, uniqueness, and positivity of solutions, and analyze their boundedness within a biologically feasible region. Local stability of equilibria is studied via linearization, while global stability is proven using Lyapunov functions. Numerical simulations complement the analytical results, demonstrating how key parameters affect the system’s long-term dynamics.</p> Neisser Pino Romero Roxana López-Cruz Copyright (c) 2025 https://creativecommons.org/licenses/by/4.0 2025-07-26 2025-07-26 12 01 67 85 10.17268/sel.mat.2025.01.06 A note on Mehler's formula https://revistas.unitru.edu.pe/index.php/SSMM/article/view/6623 <p>In this paper we propose an original proof of Mehler expansion of the Gaussian distribution in terms of probabilistic Hermite polynomials.</p> Alessandri Canchoa Quispe Sergio Camiz Eladio Ocaña Copyright (c) 2025 https://creativecommons.org/licenses/by/4.0 2025-07-26 2025-07-26 12 01 86 89 10.17268/sel.mat.2025.01.07 A note about a Morse's conjecture https://revistas.unitru.edu.pe/index.php/SSMM/article/view/6624 <p>In dynamical systems it is known that metrically transitive systems are topologically transitive. M. Morse in 1946 ([1]) conjectured that if the dynamical system has some degree of regularity, then the converse is true. In this article, we will study the Morse conjecture for R2-actions on three-dimensional manifolds and prove the following two results: The conjecture is false if we do not impose restrictions on the singular set and we will prove that The Morse’s Conjecture is valid for locally free actions.</p> Walter T. Huaraca Vargas Copyright (c) 2025 https://creativecommons.org/licenses/by/4.0 2025-07-26 2025-07-26 12 01 90 96 10.17268/sel.mat.2025.01.08 Tangential intersection curves of two surfaces in the three-dimensional Lorentz-Minkowski space https://revistas.unitru.edu.pe/index.php/SSMM/article/view/6625 <p>We present algorithms for computing the differential geometry properties of tangential intersection curves of two surfaces in the three-dimensional Lorentz-Minkowski space E31 . We compute the tangent vector of tangential intersection curves of two surfaces parametric, where the surfaces can be: spacelike, timelike, or lightlike. The first method computed the tangent vector using the equality of the projection of the second derivative vector onto the normal vector and second method computes the tangent vector by applying a rotation to a vector projected onto the tangent space, where the axis of rotation is the normal vector of the surface. In Minkowski space, there are three types of rotations, since the normal vectors can be: spacelike, lightlike, or timelike.</p> Osmar Alessio Luiz Augusto Ramos Cintra Neto Copyright (c) 2025 https://creativecommons.org/licenses/by/4.0 2025-07-26 2025-07-26 12 01 97 122 10.17268/sel.mat.2025.01.09 On the structure of the fundamental étale group of normal schemes https://revistas.unitru.edu.pe/index.php/SSMM/article/view/6626 <p>The étale fundamental group is a central tool in algebraic geometry that generalizes the topological fundamental group to the context of schemes. In this article, we explore its behavior for normal schemes, highlighting its relationship to arithmetic and geometric invariants.</p> Ronald Jesús Mas Huamán Copyright (c) 2025 https://creativecommons.org/licenses/by/4.0 2025-07-26 2025-07-26 12 01 123 131 10.17268/sel.mat.2025.01.10 The energy allocation toward life-history functions: Link between the individual and population levels https://revistas.unitru.edu.pe/index.php/SSMM/article/view/6629 <p>The population dynamics of organisms are strongly influenced by life-history strategies that result from the optimal allocation of energy to vital functions such as growth, reproduction, and survival.</p> <p>These strategies, characterized by phenotypic traits, emerge as evolutionary adaptations to specific ecological conditions and define functional trade-offs relevant facing biotic and abiotic pressures. The aim of this study is to examine the link between life history and population dynamics from a bioenergetic perspective, articulating individual and population-level processes through mathematical models that capture adaptive decisions in simulated environments described in terms of constant, decreasing, and periodic resource availability over time. Using a discrete-time mathematical model with two state variables, internal energy and survival probability, energy allocation toward reproduction and foraging is incorporated in order to determine the optimal strategy that maximizes the net reproductive rate. To solve this control problem, Pontryagin’s maximum principle is applied, using the forward–backward method to obtain optimal trajectories of allocation, energy, and survival. These trajectories are analyzed with respect to relevant physiological parameters under different scenarios of resource availability, thereby allowing the exploration of how environmental conditions influence the bioenergetic decisions of organisms.</p> Víctor Saldaña-Núñez Alex Altamirano-Fernández Ranghely Hernández-Castañeda Rodrigo Gutiérrez Copyright (c) 2025 https://creativecommons.org/licenses/by/4.0 2025-07-26 2025-07-26 12 01 132 141 10.17268/sel.mat.2025.01.11 Eigen-concepts in the multiplicative linear algebra context https://revistas.unitru.edu.pe/index.php/SSMM/article/view/6630 <p>The concept of eigenvalues is associated with the linearity one, through the structure of vectorial space. The multiplicative linear algebra is a structure in which an expression such as x^3y^2 can be considered a linear combination of variables x and y. This article is reserved to show the corresponding analogues for an Eigenvalue Theory. We exemplify its applications by introducing a connection with the analysis of a nonlinear dynamical system in the standard sense, although a linear recurrence in the multiplicative one.</p> Fernando Córdova-Lepe Franco Lara-Muñoz Ranghely Hernández-Castañeda Rodrigo Gutiérrez Copyright (c) 2025 https://creativecommons.org/licenses/by/4.0 2025-07-26 2025-07-26 12 01 142 154 10.17268/sel.mat.2025.01.12 Tangencies for Power Functions with Integer Exponent https://revistas.unitru.edu.pe/index.php/SSMM/article/view/6637 <p>Considering a power function f(x) = x^n with exponent n as a positive integer, we show that, at each of its points, there exists a unique polynomial function of degree n − 1 that is tangent to it at that point. Similarly, we verify that every power function h(x) = x^k with exponent k as a negative integer is tangent, at each of its points, to a function of the form l(x) =Sa^t.x^t, where the exponents t are integers between k + 1 and −1.</p> Cairo Henrique Vaz Cotrim Laredo Rennan Pereira Santos Copyright (c) 2025 https://creativecommons.org/licenses/by/4.0 2025-07-26 2025-07-26 12 01 155 161 10.17268/sel.mat.2025.01.13