Exact vs. Gauss-Seidel non-LTE radiation transfer solutions
  Although published in 1995, the Gauss-Seidel method for solving the non-LTE radiative transfer problem has deserved too little attention in the astrophysical community yet. Further tests of the performances and of the accuracy of the numerical scheme are provided. 
C. Quang, F. Paletou, L. Chevallier