The exponential function can be approximated with small deviation by eliminating the high order Taylor series for ax1. The major deviation of exponential function results from the ignored orders of the Taylor series, the absolute range of x (1 or 1) and the coefficient “a”. Obviously, for ax >1, the exponential function cannot be implemented by a low-order polynomial. The approximation equation, obtained by eliminating the higher order terms of (1) with small error for ax1, can be written as