Perturbation Theory for the Systems of Ordinary Linear Differential   Equations with Periodical Coefficients
  The method, proposed in the given work, allows the application of well developed standard methods used in quantum mechanics for approximate solution of the systems of ordinary linear differential equations with periodical coefficients. 
A.G. Kvirikadze, M.D. Zviadadze, T.V. Tavdgiridze, I.G. Tavelidze