Integrable conditions for Dirac Equation and Schr\"odinger equation
  By constructing the commutative operators chain, we derive the integrable conditions for solving the eigenfunctions of Dirac equation and Schr\"odinger equation. These commutative relations correspond to the intrinsic symmetry of the physical system, which are equivalent to the original partial differential equation can be solved by separation of variables. Detailed calculation shows that, only a few cases can be completely solved by separation of variables. In general cases, we have to solve the Dirac equation and Schr\"odinger equation by effective perturbation or approximation methods, especially in the cases including nonlinear potential or self interactive potentials. 
Ying-Qiu Gu