Equations Differentielles a Points Singuliers Reguliers

The subject of partial differential equations holds an exciting and special position in mathematics. Partial differential equations were not consciously created as a subject but emerged in the 18th century as ordinary differential equations failed to describe the physical principles being studied. The subject was originally developed by the major names of mathematics, in particular, Leonard Euler and Joseph-Louis Lagrange who studied waves on strings; Daniel Bernoulli and Euler who considered potential theory, with later developments by Adrien-Marie Legendre and Pierre-Simon Laplace; and Joseph Fourier's famous work on series expansions for the heat equation. Many of the greatest advances in modern science have been based on discovering the underlying partial differential equation for the process in question. J ames Clerk Maxwell, for example, put electricity and magnetism into a unified theory by estab­ lishing Maxwell's equations for electromagnetic theory, which gave solutions for problems in radio wave propagation, the diffraction of light and X-ray developments. Schrodinger's equation for quantum mechankal processes at the atomic level leads to experimentally verifiable results which have changed the face of atomic physics and chemistry in the 20th century. In fluid mechanics, the Navier-Stokes' equations form a basis for huge number-crunching activities associated with such widely disparate topics as weather forcasting and the design of supersonic aircraft. Inevitably the study of partial differential equations is a large undertaking, and falls into several areas of mathematics.

The aim of this reprint is to highlight the significance of difference equations and their applications in applied mathematics. Difference equations provide a robust and widely recognized framework for modeling complex dynamical systems. In recent years, non-integer order derivative operators have gained attention, particularly for understanding anomalous behaviors in social and physical sciences. The following Special Issue introduces several important developments, including new partial fractional derivatives, a novel nonlinear delayed integral inequality for studying integro-differential equations, and a neural network approach for solving nonlinear partial differential equations. The existence and uniqueness of solutions for nonlinear differential equations with impulses at variable times are discussed, as well as the oscillatory behavior of nonlinear second-order differential equations. Ultimately, this reprint bridges theory and application, offering novel insights with a focus on differential and difference equations.