This book considers the Cauchy problem for a system of ordinary differential equations with a small parameter, filling in areas that have not been extensively covered in the existing literature. The well-known types of equations, such as the regularly perturbed Cauchy problem and the Tikhonov problem, are dealt with, but new ones are also treated, such as the quasiregular Cauchy problem, and the Cauchy problem with double singularity. For each type of problem, series are constructed which generalise the well-known series of PoincarA(c) and Vasilyeva-Imanaliyev. It is shown that these series are asymptotic expansions of the solution, or converge to the solution on a segment, semiaxis or asymptotically large time intervals. Theorems are proved providing numerical estimates for the remainder term of the asymptotics, the time interval of the solution existence, and the small parameter values. Audience: This volume will be of interest to researchers and graduate students specialising in ordinary differential equations.

In this book we consider a Cauchy problem for a system of ordinary differential equations with a small parameter. The book is divided into th ree parts according to three ways of involving the small parameter in the system. In Part 1 we study the quasiregular Cauchy problem. Th at is, a problem with the singularity included in a bounded function j , which depends on time and a small parameter. This problem is a generalization of the regu larly perturbed Cauchy problem studied by Poincare [35]. Some differential equations which are solved by the averaging method can be reduced to a quasiregular Cauchy problem. As an example, in Chapter 2 we consider the van der Pol problem. In Part 2 we study the Tikhonov problem. This is, a Cauchy problem for a system of ordinary differential equations where the coefficients by the derivatives are integer degrees of a small parameter.