Simple and accurate approximations to Dirichlet $L$-functions

Abstract

We extend the quadrature method developed in [10] to Dirichlet $L$-functions associated with primitive characters. The approximations combine finite Dirichlet sums with correction terms whose quadrature coefficients can be precomputed for each character. Numerical experiments demonstrate high accuracy in the critical strip and in other vertical strips. We also describe how to combine these approximations with direct summation and Euler--Maclaurin summation to evaluate $L(s,\chi )$ throughout the complex plane.

arXiv comment10 pages, 2 figures