We consider the approximation of a weakly coupled system of two singularly perturbed reaction-diffusion equations, with the finite element method. The first differential equation contains a small parameter multiplying the highest derivative, while the second does not. As a result, the first component of the solution to the system will contain boundary layers and our goal is to construct and ana...

The present paper deals with a survey of numerical techniques for solving nonlinear elliptic singular perturbation problems, developed by numerous researchers in a chronological order as the field developed year after year from 1985. A large amount of research material related to nonlinear elliptic singularly perturbed problems has been collected with the aim of introduction to some of the idea...

We investigate the singular Weyl–Titchmarsh m-function of perturbed spherical Schrödinger operators (also known as Bessel operators) under the assumption that the perturbation q(x) satisfies xq(x) ∈ L(0, 1). We show existence plus detailed properties of a fundamental system of solutions which are entire with respect to the energy parameter. Based on this we show that the singular m-function bel...