Introduction

Abstract

Mathematical modeling is one of the most important and powerful methods for studying phenomena occurring in our universe. Generally speaking, such a model is made up of one or several equations from which we aim to determine one or several unknown quantities of interest in terms of other, prescribed, quantities. The unknown quantities turn out in many cases to be functions of a set of variables. Since very often the physical or empirical laws governing evolutionary processes implicate the rates of change of these functions with respect to their variables, and since rates of change are represented in mathematics by derivatives, it is important for us to gain knowledge of how to solve equations where the unknown functions occur together with their derivatives.