This paper describes a method to obtain an analytical expression for the nonlinear dependence of the ferroelectric polarization on the external electric field. To find analytical dependence, used a special Kml-function of second order. Listed structure built of series and groups of series representing Kml-function at any point in the complex plane. Analyzed domain of convergence of series , received as a boundary condition. To show the application of the method, as an example used a ferroelectric polymer polyvinylidene fluoride (PVDF–TrFE ).
