Quantization of the classical action and eigenvalue problem
  The eigenvalue problem in quantum mechanics is reduced to quantization of the classical action of the physical system. State function of the system, $\psi_0(\phi)$, is written in the form of superposition of two plane waves in the phase space. Quantization condition is derived from the basic requirements of continuity and finiteness for $\psi_0(\phi)$ in the whole region. 
M.N. Sergeenko