Exponential Sum Approximations for t−β
Given β > 0 and δ > 0, the function t−β may be approximated for t in a compact interval [δ, T] by a sum of terms of the form we−at, with parameters w > 0 and a > 0. One such an approximation, studied by Beylkin and Monzón (Appl. Comput. Harmon. Anal. 28:131–149, 2010), is obtained by applying the trapezoidal rule to an integral representation of t−β, after which Prony’s method is applied to reduce the number of terms in the sum with essentially no loss of accuracy. We review this method, and then describe a similar approach based on an alternative integral representation. The main difference is that the new approach achieves much better results before the application of Prony’s method; after applying Prony’s method the performance of both is much the same.