Be careful with the equivalence of different ansätz of improved tanh-function method for nonlinear models

Exact solutions of nonlinear models might explain real physical, engineering and biophysical problems, including blood pressure waves, αα-helical protein, matter wave and hardening spring effect, and so on. We re-study the breaking soliton model and obtain eleven kinds of variable separation solution by means of the improved tanh-function method with three different ansätz, that is, positive-power ansatz, radical sign combined ansatz, and positive and negative power-symmetric ansatz. By careful analysis of these exact solutions, we find that these seemly independent variable separation solutions actually depend on each other. Therefore, different ansätz of improved tanh-function method are equivalent.