Abstract
In this paper, we propose a method to approximate nonlinear ordinary differential equations to nonlinear retarded systems. Applying a parturbation method into a Duffingtype retarded system, we construct a primary approximation model. In order to improve accuracy of the model, we then modify system parameters of the model based on an averaging method to derive a modified approximation model. Errors among the original retarded system and the two models are evaluated. The modified primary approximation model results in the best approximation of the nonlinear retarded system.
