An improper integral of a function of real variable representing a given physical quantity is often calculated by considering it as part of a complex integral whose path of integration, in a limiting process, tends to include the whole real axis, approaching the real poles of the integrand such as to produce physically acceptable results. In this work, we describe the methods usually employed in the evaluation of such integrals, with emphasis on how physical conditions determine the way the limits are to be carried out. In addition, we solve three classical problems to exemplify the techniques presented.
improper integral; prescription; i-epsilon; principal value
