Asymptotic preserving schemes for the Klein-Gordon equation in the   non-relativistic limit regime
  We consider the Klein-Gordon equation in the non-relativistic limit regime, i.e. the speed of light c tending to infinity. We construct an asymptotic expansion for the solution with respect to the small parameter depending on the inverse of the square of the speed of light. As the first terms of this asymptotic can easily be simulated our approach allows us to construct numerical algorithms that are robust with respect to the large parameter c producing high oscillations in the exact solution. 
Erwan Faou and Katharina Schratz
math.NA