The theory of singular perturbations is a fascinating mixture of rigorous analysis, heuristic reasoning and induction from experience. The aim of this book is to give these aspects a coherent presentation. The scope of the book is limited to problems exhibiting the so-called boundary layer behaviour.
Read more at http://ebookee.org/Asymptotic-Analysis-of-Singular-Perturbations_1166502.html#xL56SuQTgQi1AW1b.99