Pole-type singularities and the numerical conformal mapping of doubly-connected domains

Let f be the function which maps conformally a given doubly-connected domain Ω onto a circular annulus, and let $\text{H(z)=}\text{f′(z)}\text{f(z)}\text{?}\text{1}\text{z}$. In this paper we consider the problem of determining the main singularities of the function H in compl($\text{Ω∪?Ω}$). Our purpose is to provide information regarding the location and nature of such singularities, and to explain how this information can be used to improve the efficiency of certain expansion methods for numerical conformal mapping.