“…As is known, the more used methods are diagonalization [2,3], quasiclassical approach [4], continuous analogue of Newton's method [5], different versions of perturbation theory [6], normal form method [7,8,9,10,11], finite-element method [12], 1/N expansion [13], oscillator representation [14], variational and operational methods [15,16,17], simplectic method [18] and etc.…”