Models of white dwarfs under rapid uniform or differential rotation; numerical approach: The approximative phase

In this paper, we extend and generalize Chandrasekhar's perturbation method on rotating white dwarfs. In particular, we include terms up to third-order in the perturbation parameter, in order to study rapid and critical rotations. We also construct a generalized model of rotation which includes as subcases both uniform and differential rotations. The numerical method, described in the present paper, is required for a subsequent quantitative treatment of the particular problem.