New representation of two-loop propagator and vertex functions
  We present a new method of calculating scalar propagator and vertex functions in the two-loop approximation, for arbitrary masses of particles. It is based on a double integral representation, suitable for numerical evaluation. Real and imaginary parts of the diagrams are calculated separately, so that there is no need to use complex arithmetics in the numerical program. 
Andrzej Czarnecki, Ulrich Kilian and Dirk Kreimer